block: Fix list corruption of blk stats callback list

[sfrench/cifs-2.6.git] / kernel / audit.c

/* audit.c -- Auditing support
 * Gateway between the kernel (e.g., selinux) and the user-space audit daemon.
 * System-call specific features have moved to auditsc.c
 *
 * Copyright 2003-2007 Red Hat Inc., Durham, North Carolina.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Written by Rickard E. (Rik) Faith <faith@redhat.com>
 *
 * Goals: 1) Integrate fully with Security Modules.
 *        2) Minimal run-time overhead:
 *           a) Minimal when syscall auditing is disabled (audit_enable=0).
 *           b) Small when syscall auditing is enabled and no audit record
 *              is generated (defer as much work as possible to record
 *              generation time):
 *              i) context is allocated,
 *              ii) names from getname are stored without a copy, and
 *              iii) inode information stored from path_lookup.
 *        3) Ability to disable syscall auditing at boot time (audit=0).
 *        4) Usable by other parts of the kernel (if audit_log* is called,
 *           then a syscall record will be generated automatically for the
 *           current syscall).
 *        5) Netlink interface to user-space.
 *        6) Support low-overhead kernel-based filtering to minimize the
 *           information that must be passed to user-space.
 *
 * Example user-space utilities: http://people.redhat.com/sgrubb/audit/
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/file.h>
#include <linux/init.h>
#include <linux/types.h>
#include <linux/atomic.h>
#include <linux/mm.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/kthread.h>
#include <linux/kernel.h>
#include <linux/syscalls.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <linux/mutex.h>
#include <linux/gfp.h>

#include <linux/audit.h>

#include <net/sock.h>
#include <net/netlink.h>
#include <linux/skbuff.h>
#ifdef CONFIG_SECURITY
#include <linux/security.h>
#endif
#include <linux/freezer.h>
#include <linux/pid_namespace.h>
#include <net/netns/generic.h>

#include "audit.h"

/* No auditing will take place until audit_initialized == AUDIT_INITIALIZED.
 * (Initialization happens after skb_init is called.) */
#define AUDIT_DISABLED          -1
#define AUDIT_UNINITIALIZED     0
#define AUDIT_INITIALIZED       1
static int      audit_initialized;

#define AUDIT_OFF       0
#define AUDIT_ON        1
#define AUDIT_LOCKED    2
u32             audit_enabled;
u32             audit_ever_enabled;

EXPORT_SYMBOL_GPL(audit_enabled);

/* Default state when kernel boots without any parameters. */
static u32      audit_default;

/* If auditing cannot proceed, audit_failure selects what happens. */
static u32      audit_failure = AUDIT_FAIL_PRINTK;

/* private audit network namespace index */
static unsigned int audit_net_id;

/**
 * struct audit_net - audit private network namespace data
 * @sk: communication socket
 */
struct audit_net {
        struct sock *sk;
};

/**
 * struct auditd_connection - kernel/auditd connection state
 * @pid: auditd PID
 * @portid: netlink portid
 * @net: the associated network namespace
 * @lock: spinlock to protect write access
 *
 * Description:
 * This struct is RCU protected; you must either hold the RCU lock for reading
 * or the included spinlock for writing.
 */
static struct auditd_connection {
        int pid;
        u32 portid;
        struct net *net;
        spinlock_t lock;
} auditd_conn;

/* If audit_rate_limit is non-zero, limit the rate of sending audit records
 * to that number per second.  This prevents DoS attacks, but results in
 * audit records being dropped. */
static u32      audit_rate_limit;

/* Number of outstanding audit_buffers allowed.
 * When set to zero, this means unlimited. */
static u32      audit_backlog_limit = 64;
#define AUDIT_BACKLOG_WAIT_TIME (60 * HZ)
static u32      audit_backlog_wait_time = AUDIT_BACKLOG_WAIT_TIME;

/* The identity of the user shutting down the audit system. */
kuid_t          audit_sig_uid = INVALID_UID;
pid_t           audit_sig_pid = -1;
u32             audit_sig_sid = 0;

/* Records can be lost in several ways:
   0) [suppressed in audit_alloc]
   1) out of memory in audit_log_start [kmalloc of struct audit_buffer]
   2) out of memory in audit_log_move [alloc_skb]
   3) suppressed due to audit_rate_limit
   4) suppressed due to audit_backlog_limit
*/
static atomic_t audit_lost = ATOMIC_INIT(0);

/* Hash for inode-based rules */
struct list_head audit_inode_hash[AUDIT_INODE_BUCKETS];

/* The audit_freelist is a list of pre-allocated audit buffers (if more
 * than AUDIT_MAXFREE are in use, the audit buffer is freed instead of
 * being placed on the freelist). */
static DEFINE_SPINLOCK(audit_freelist_lock);
static int         audit_freelist_count;
static LIST_HEAD(audit_freelist);

/* queue msgs to send via kauditd_task */
static struct sk_buff_head audit_queue;
static void kauditd_hold_skb(struct sk_buff *skb);
/* queue msgs due to temporary unicast send problems */
static struct sk_buff_head audit_retry_queue;
/* queue msgs waiting for new auditd connection */
static struct sk_buff_head audit_hold_queue;

/* queue servicing thread */
static struct task_struct *kauditd_task;
static DECLARE_WAIT_QUEUE_HEAD(kauditd_wait);

/* waitqueue for callers who are blocked on the audit backlog */
static DECLARE_WAIT_QUEUE_HEAD(audit_backlog_wait);

static struct audit_features af = {.vers = AUDIT_FEATURE_VERSION,
                                   .mask = -1,
                                   .features = 0,
                                   .lock = 0,};

static char *audit_feature_names[2] = {
        "only_unset_loginuid",
        "loginuid_immutable",
};


/* Serialize requests from userspace. */
DEFINE_MUTEX(audit_cmd_mutex);

/* AUDIT_BUFSIZ is the size of the temporary buffer used for formatting
 * audit records.  Since printk uses a 1024 byte buffer, this buffer
 * should be at least that large. */
#define AUDIT_BUFSIZ 1024

/* AUDIT_MAXFREE is the number of empty audit_buffers we keep on the
 * audit_freelist.  Doing so eliminates many kmalloc/kfree calls. */
#define AUDIT_MAXFREE  (2*NR_CPUS)

/* The audit_buffer is used when formatting an audit record.  The caller
 * locks briefly to get the record off the freelist or to allocate the
 * buffer, and locks briefly to send the buffer to the netlink layer or
 * to place it on a transmit queue.  Multiple audit_buffers can be in
 * use simultaneously. */
struct audit_buffer {
        struct list_head     list;
        struct sk_buff       *skb;      /* formatted skb ready to send */
        struct audit_context *ctx;      /* NULL or associated context */
        gfp_t                gfp_mask;
};

struct audit_reply {
        __u32 portid;
        struct net *net;
        struct sk_buff *skb;
};

/**
 * auditd_test_task - Check to see if a given task is an audit daemon
 * @task: the task to check
 *
 * Description:
 * Return 1 if the task is a registered audit daemon, 0 otherwise.
 */
int auditd_test_task(const struct task_struct *task)
{
        int rc;

        rcu_read_lock();
        rc = (auditd_conn.pid && task->tgid == auditd_conn.pid ? 1 : 0);
        rcu_read_unlock();

        return rc;
}

/**
 * audit_get_sk - Return the audit socket for the given network namespace
 * @net: the destination network namespace
 *
 * Description:
 * Returns the sock pointer if valid, NULL otherwise.  The caller must ensure
 * that a reference is held for the network namespace while the sock is in use.
 */
static struct sock *audit_get_sk(const struct net *net)
{
        struct audit_net *aunet;

        if (!net)
                return NULL;

        aunet = net_generic(net, audit_net_id);
        return aunet->sk;
}

static void audit_set_portid(struct audit_buffer *ab, __u32 portid)
{
        if (ab) {
                struct nlmsghdr *nlh = nlmsg_hdr(ab->skb);
                nlh->nlmsg_pid = portid;
        }
}

void audit_panic(const char *message)
{
        switch (audit_failure) {
        case AUDIT_FAIL_SILENT:
                break;
        case AUDIT_FAIL_PRINTK:
                if (printk_ratelimit())
                        pr_err("%s\n", message);
                break;
        case AUDIT_FAIL_PANIC:
                panic("audit: %s\n", message);
                break;
        }
}

static inline int audit_rate_check(void)
{
        static unsigned long    last_check = 0;
        static int              messages   = 0;
        static DEFINE_SPINLOCK(lock);
        unsigned long           flags;
        unsigned long           now;
        unsigned long           elapsed;
        int                     retval     = 0;

        if (!audit_rate_limit) return 1;

        spin_lock_irqsave(&lock, flags);
        if (++messages < audit_rate_limit) {
                retval = 1;
        } else {
                now     = jiffies;
                elapsed = now - last_check;
                if (elapsed > HZ) {
                        last_check = now;
                        messages   = 0;
                        retval     = 1;
                }
        }
        spin_unlock_irqrestore(&lock, flags);

        return retval;
}

/**
 * audit_log_lost - conditionally log lost audit message event
 * @message: the message stating reason for lost audit message
 *
 * Emit at least 1 message per second, even if audit_rate_check is
 * throttling.
 * Always increment the lost messages counter.
*/
void audit_log_lost(const char *message)
{
        static unsigned long    last_msg = 0;
        static DEFINE_SPINLOCK(lock);
        unsigned long           flags;
        unsigned long           now;
        int                     print;

        atomic_inc(&audit_lost);

        print = (audit_failure == AUDIT_FAIL_PANIC || !audit_rate_limit);

        if (!print) {
                spin_lock_irqsave(&lock, flags);
                now = jiffies;
                if (now - last_msg > HZ) {
                        print = 1;
                        last_msg = now;
                }
                spin_unlock_irqrestore(&lock, flags);
        }

        if (print) {
                if (printk_ratelimit())
                        pr_warn("audit_lost=%u audit_rate_limit=%u audit_backlog_limit=%u\n",
                                atomic_read(&audit_lost),
                                audit_rate_limit,
                                audit_backlog_limit);
                audit_panic(message);
        }
}

static int audit_log_config_change(char *function_name, u32 new, u32 old,
                                   int allow_changes)
{
        struct audit_buffer *ab;
        int rc = 0;

        ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE);
        if (unlikely(!ab))
                return rc;
        audit_log_format(ab, "%s=%u old=%u", function_name, new, old);
        audit_log_session_info(ab);
        rc = audit_log_task_context(ab);
        if (rc)
                allow_changes = 0; /* Something weird, deny request */
        audit_log_format(ab, " res=%d", allow_changes);
        audit_log_end(ab);
        return rc;
}

static int audit_do_config_change(char *function_name, u32 *to_change, u32 new)
{
        int allow_changes, rc = 0;
        u32 old = *to_change;

        /* check if we are locked */
        if (audit_enabled == AUDIT_LOCKED)
                allow_changes = 0;
        else
                allow_changes = 1;

        if (audit_enabled != AUDIT_OFF) {
                rc = audit_log_config_change(function_name, new, old, allow_changes);
                if (rc)
                        allow_changes = 0;
        }

        /* If we are allowed, make the change */
        if (allow_changes == 1)
                *to_change = new;
        /* Not allowed, update reason */
        else if (rc == 0)
                rc = -EPERM;
        return rc;
}

static int audit_set_rate_limit(u32 limit)
{
        return audit_do_config_change("audit_rate_limit", &audit_rate_limit, limit);
}

static int audit_set_backlog_limit(u32 limit)
{
        return audit_do_config_change("audit_backlog_limit", &audit_backlog_limit, limit);
}

static int audit_set_backlog_wait_time(u32 timeout)
{
        return audit_do_config_change("audit_backlog_wait_time",
                                      &audit_backlog_wait_time, timeout);
}

static int audit_set_enabled(u32 state)
{
        int rc;
        if (state > AUDIT_LOCKED)
                return -EINVAL;

        rc =  audit_do_config_change("audit_enabled", &audit_enabled, state);
        if (!rc)
                audit_ever_enabled |= !!state;

        return rc;
}

static int audit_set_failure(u32 state)
{
        if (state != AUDIT_FAIL_SILENT
            && state != AUDIT_FAIL_PRINTK
            && state != AUDIT_FAIL_PANIC)
                return -EINVAL;

        return audit_do_config_change("audit_failure", &audit_failure, state);
}

/**
 * auditd_set - Set/Reset the auditd connection state
 * @pid: auditd PID
 * @portid: auditd netlink portid
 * @net: auditd network namespace pointer
 *
 * Description:
 * This function will obtain and drop network namespace references as
 * necessary.
 */
static void auditd_set(int pid, u32 portid, struct net *net)
{
        unsigned long flags;

        spin_lock_irqsave(&auditd_conn.lock, flags);
        auditd_conn.pid = pid;
        auditd_conn.portid = portid;
        if (auditd_conn.net)
                put_net(auditd_conn.net);
        if (net)
                auditd_conn.net = get_net(net);
        else
                auditd_conn.net = NULL;
        spin_unlock_irqrestore(&auditd_conn.lock, flags);
}

/**
 * auditd_reset - Disconnect the auditd connection
 *
 * Description:
 * Break the auditd/kauditd connection and move all the queued records into the
 * hold queue in case auditd reconnects.
 */
static void auditd_reset(void)
{
        struct sk_buff *skb;

        /* if it isn't already broken, break the connection */
        rcu_read_lock();
        if (auditd_conn.pid)
                auditd_set(0, 0, NULL);
        rcu_read_unlock();

        /* flush all of the main and retry queues to the hold queue */
        while ((skb = skb_dequeue(&audit_retry_queue)))
                kauditd_hold_skb(skb);
        while ((skb = skb_dequeue(&audit_queue)))
                kauditd_hold_skb(skb);
}

/**
 * kauditd_print_skb - Print the audit record to the ring buffer
 * @skb: audit record
 *
 * Whatever the reason, this packet may not make it to the auditd connection
 * so write it via printk so the information isn't completely lost.
 */
static void kauditd_printk_skb(struct sk_buff *skb)
{
        struct nlmsghdr *nlh = nlmsg_hdr(skb);
        char *data = nlmsg_data(nlh);

        if (nlh->nlmsg_type != AUDIT_EOE && printk_ratelimit())
                pr_notice("type=%d %s\n", nlh->nlmsg_type, data);
}

/**
 * kauditd_rehold_skb - Handle a audit record send failure in the hold queue
 * @skb: audit record
 *
 * Description:
 * This should only be used by the kauditd_thread when it fails to flush the
 * hold queue.
 */
static void kauditd_rehold_skb(struct sk_buff *skb)
{
        /* put the record back in the queue at the same place */
        skb_queue_head(&audit_hold_queue, skb);

        /* fail the auditd connection */
        auditd_reset();
}

/**
 * kauditd_hold_skb - Queue an audit record, waiting for auditd
 * @skb: audit record
 *
 * Description:
 * Queue the audit record, waiting for an instance of auditd.  When this
 * function is called we haven't given up yet on sending the record, but things
 * are not looking good.  The first thing we want to do is try to write the
 * record via printk and then see if we want to try and hold on to the record
 * and queue it, if we have room.  If we want to hold on to the record, but we
 * don't have room, record a record lost message.
 */
static void kauditd_hold_skb(struct sk_buff *skb)
{
        /* at this point it is uncertain if we will ever send this to auditd so
         * try to send the message via printk before we go any further */
        kauditd_printk_skb(skb);

        /* can we just silently drop the message? */
        if (!audit_default) {
                kfree_skb(skb);
                return;
        }

        /* if we have room, queue the message */
        if (!audit_backlog_limit ||
            skb_queue_len(&audit_hold_queue) < audit_backlog_limit) {
                skb_queue_tail(&audit_hold_queue, skb);
                return;
        }

        /* we have no other options - drop the message */
        audit_log_lost("kauditd hold queue overflow");
        kfree_skb(skb);

        /* fail the auditd connection */
        auditd_reset();
}

/**
 * kauditd_retry_skb - Queue an audit record, attempt to send again to auditd
 * @skb: audit record
 *
 * Description:
 * Not as serious as kauditd_hold_skb() as we still have a connected auditd,
 * but for some reason we are having problems sending it audit records so
 * queue the given record and attempt to resend.
 */
static void kauditd_retry_skb(struct sk_buff *skb)
{
        /* NOTE: because records should only live in the retry queue for a
         * short period of time, before either being sent or moved to the hold
         * queue, we don't currently enforce a limit on this queue */
        skb_queue_tail(&audit_retry_queue, skb);
}

/**
 * auditd_send_unicast_skb - Send a record via unicast to auditd
 * @skb: audit record
 *
 * Description:
 * Send a skb to the audit daemon, returns positive/zero values on success and
 * negative values on failure; in all cases the skb will be consumed by this
 * function.  If the send results in -ECONNREFUSED the connection with auditd
 * will be reset.  This function may sleep so callers should not hold any locks
 * where this would cause a problem.
 */
static int auditd_send_unicast_skb(struct sk_buff *skb)
{
        int rc;
        u32 portid;
        struct net *net;
        struct sock *sk;

        /* NOTE: we can't call netlink_unicast while in the RCU section so
         *       take a reference to the network namespace and grab local
         *       copies of the namespace, the sock, and the portid; the
         *       namespace and sock aren't going to go away while we hold a
         *       reference and if the portid does become invalid after the RCU
         *       section netlink_unicast() should safely return an error */

        rcu_read_lock();
        if (!auditd_conn.pid) {
                rcu_read_unlock();
                rc = -ECONNREFUSED;
                goto err;
        }
        net = auditd_conn.net;
        get_net(net);
        sk = audit_get_sk(net);
        portid = auditd_conn.portid;
        rcu_read_unlock();

        rc = netlink_unicast(sk, skb, portid, 0);
        put_net(net);
        if (rc < 0)
                goto err;

        return rc;

err:
        if (rc == -ECONNREFUSED)
                auditd_reset();
        return rc;
}

/**
 * kauditd_send_queue - Helper for kauditd_thread to flush skb queues
 * @sk: the sending sock
 * @portid: the netlink destination
 * @queue: the skb queue to process
 * @retry_limit: limit on number of netlink unicast failures
 * @skb_hook: per-skb hook for additional processing
 * @err_hook: hook called if the skb fails the netlink unicast send
 *
 * Description:
 * Run through the given queue and attempt to send the audit records to auditd,
 * returns zero on success, negative values on failure.  It is up to the caller
 * to ensure that the @sk is valid for the duration of this function.
 *
 */
static int kauditd_send_queue(struct sock *sk, u32 portid,
                              struct sk_buff_head *queue,
                              unsigned int retry_limit,
                              void (*skb_hook)(struct sk_buff *skb),
                              void (*err_hook)(struct sk_buff *skb))
{
        int rc = 0;
        struct sk_buff *skb;
        static unsigned int failed = 0;

        /* NOTE: kauditd_thread takes care of all our locking, we just use
         *       the netlink info passed to us (e.g. sk and portid) */

        while ((skb = skb_dequeue(queue))) {
                /* call the skb_hook for each skb we touch */
                if (skb_hook)
                        (*skb_hook)(skb);

                /* can we send to anyone via unicast? */
                if (!sk) {
                        if (err_hook)
                                (*err_hook)(skb);
                        continue;
                }

                /* grab an extra skb reference in case of error */
                skb_get(skb);
                rc = netlink_unicast(sk, skb, portid, 0);
                if (rc < 0) {
                        /* fatal failure for our queue flush attempt? */
                        if (++failed >= retry_limit ||
                            rc == -ECONNREFUSED || rc == -EPERM) {
                                /* yes - error processing for the queue */
                                sk = NULL;
                                if (err_hook)
                                        (*err_hook)(skb);
                                if (!skb_hook)
                                        goto out;
                                /* keep processing with the skb_hook */
                                continue;
                        } else
                                /* no - requeue to preserve ordering */
                                skb_queue_head(queue, skb);
                } else {
                        /* it worked - drop the extra reference and continue */
                        consume_skb(skb);
                        failed = 0;
                }
        }

out:
        return (rc >= 0 ? 0 : rc);
}

/*
 * kauditd_send_multicast_skb - Send a record to any multicast listeners
 * @skb: audit record
 *
 * Description:
 * Write a multicast message to anyone listening in the initial network
 * namespace.  This function doesn't consume an skb as might be expected since
 * it has to copy it anyways.
 */
static void kauditd_send_multicast_skb(struct sk_buff *skb)
{
        struct sk_buff *copy;
        struct sock *sock = audit_get_sk(&init_net);
        struct nlmsghdr *nlh;

        /* NOTE: we are not taking an additional reference for init_net since
         *       we don't have to worry about it going away */

        if (!netlink_has_listeners(sock, AUDIT_NLGRP_READLOG))
                return;

        /*
         * The seemingly wasteful skb_copy() rather than bumping the refcount
         * using skb_get() is necessary because non-standard mods are made to
         * the skb by the original kaudit unicast socket send routine.  The
         * existing auditd daemon assumes this breakage.  Fixing this would
         * require co-ordinating a change in the established protocol between
         * the kaudit kernel subsystem and the auditd userspace code.  There is
         * no reason for new multicast clients to continue with this
         * non-compliance.
         */
        copy = skb_copy(skb, GFP_KERNEL);
        if (!copy)
                return;
        nlh = nlmsg_hdr(copy);
        nlh->nlmsg_len = skb->len;

        nlmsg_multicast(sock, copy, 0, AUDIT_NLGRP_READLOG, GFP_KERNEL);
}

/**
 * kauditd_thread - Worker thread to send audit records to userspace
 * @dummy: unused
 */
static int kauditd_thread(void *dummy)
{
        int rc;
        u32 portid = 0;
        struct net *net = NULL;
        struct sock *sk = NULL;

#define UNICAST_RETRIES 5

        set_freezable();
        while (!kthread_should_stop()) {
                /* NOTE: see the lock comments in auditd_send_unicast_skb() */
                rcu_read_lock();
                if (!auditd_conn.pid) {
                        rcu_read_unlock();
                        goto main_queue;
                }
                net = auditd_conn.net;
                get_net(net);
                sk = audit_get_sk(net);
                portid = auditd_conn.portid;
                rcu_read_unlock();

                /* attempt to flush the hold queue */
                rc = kauditd_send_queue(sk, portid,
                                        &audit_hold_queue, UNICAST_RETRIES,
                                        NULL, kauditd_rehold_skb);
                if (rc < 0) {
                        sk = NULL;
                        goto main_queue;
                }

                /* attempt to flush the retry queue */
                rc = kauditd_send_queue(sk, portid,
                                        &audit_retry_queue, UNICAST_RETRIES,
                                        NULL, kauditd_hold_skb);
                if (rc < 0) {
                        sk = NULL;
                        goto main_queue;
                }

main_queue:
                /* process the main queue - do the multicast send and attempt
                 * unicast, dump failed record sends to the retry queue; if
                 * sk == NULL due to previous failures we will just do the
                 * multicast send and move the record to the retry queue */
                kauditd_send_queue(sk, portid, &audit_queue, 1,
                                   kauditd_send_multicast_skb,
                                   kauditd_retry_skb);

                /* drop our netns reference, no auditd sends past this line */
                if (net) {
                        put_net(net);
                        net = NULL;
                }
                sk = NULL;

                /* we have processed all the queues so wake everyone */
                wake_up(&audit_backlog_wait);

                /* NOTE: we want to wake up if there is anything on the queue,
                 *       regardless of if an auditd is connected, as we need to
                 *       do the multicast send and rotate records from the
                 *       main queue to the retry/hold queues */
                wait_event_freezable(kauditd_wait,
                                     (skb_queue_len(&audit_queue) ? 1 : 0));
        }

        return 0;
}

int audit_send_list(void *_dest)
{
        struct audit_netlink_list *dest = _dest;
        struct sk_buff *skb;
        struct sock *sk = audit_get_sk(dest->net);

        /* wait for parent to finish and send an ACK */
        mutex_lock(&audit_cmd_mutex);
        mutex_unlock(&audit_cmd_mutex);

        while ((skb = __skb_dequeue(&dest->q)) != NULL)
                netlink_unicast(sk, skb, dest->portid, 0);

        put_net(dest->net);
        kfree(dest);

        return 0;
}

struct sk_buff *audit_make_reply(__u32 portid, int seq, int type, int done,
                                 int multi, const void *payload, int size)
{
        struct sk_buff  *skb;
        struct nlmsghdr *nlh;
        void            *data;
        int             flags = multi ? NLM_F_MULTI : 0;
        int             t     = done  ? NLMSG_DONE  : type;

        skb = nlmsg_new(size, GFP_KERNEL);
        if (!skb)
                return NULL;

        nlh     = nlmsg_put(skb, portid, seq, t, size, flags);
        if (!nlh)
                goto out_kfree_skb;
        data = nlmsg_data(nlh);
        memcpy(data, payload, size);
        return skb;

out_kfree_skb:
        kfree_skb(skb);
        return NULL;
}

static int audit_send_reply_thread(void *arg)
{
        struct audit_reply *reply = (struct audit_reply *)arg;
        struct sock *sk = audit_get_sk(reply->net);

        mutex_lock(&audit_cmd_mutex);
        mutex_unlock(&audit_cmd_mutex);

        /* Ignore failure. It'll only happen if the sender goes away,
           because our timeout is set to infinite. */
        netlink_unicast(sk, reply->skb, reply->portid, 0);
        put_net(reply->net);
        kfree(reply);
        return 0;
}

/**
 * audit_send_reply - send an audit reply message via netlink
 * @request_skb: skb of request we are replying to (used to target the reply)
 * @seq: sequence number
 * @type: audit message type
 * @done: done (last) flag
 * @multi: multi-part message flag
 * @payload: payload data
 * @size: payload size
 *
 * Allocates an skb, builds the netlink message, and sends it to the port id.
 * No failure notifications.
 */
static void audit_send_reply(struct sk_buff *request_skb, int seq, int type, int done,
                             int multi, const void *payload, int size)
{
        u32 portid = NETLINK_CB(request_skb).portid;
        struct net *net = sock_net(NETLINK_CB(request_skb).sk);
        struct sk_buff *skb;
        struct task_struct *tsk;
        struct audit_reply *reply = kmalloc(sizeof(struct audit_reply),
                                            GFP_KERNEL);

        if (!reply)
                return;

        skb = audit_make_reply(portid, seq, type, done, multi, payload, size);
        if (!skb)
                goto out;

        reply->net = get_net(net);
        reply->portid = portid;
        reply->skb = skb;

        tsk = kthread_run(audit_send_reply_thread, reply, "audit_send_reply");
        if (!IS_ERR(tsk))
                return;
        kfree_skb(skb);
out:
        kfree(reply);
}

/*
 * Check for appropriate CAP_AUDIT_ capabilities on incoming audit
 * control messages.
 */
static int audit_netlink_ok(struct sk_buff *skb, u16 msg_type)
{
        int err = 0;

        /* Only support initial user namespace for now. */
        /*
         * We return ECONNREFUSED because it tricks userspace into thinking
         * that audit was not configured into the kernel.  Lots of users
         * configure their PAM stack (because that's what the distro does)
         * to reject login if unable to send messages to audit.  If we return
         * ECONNREFUSED the PAM stack thinks the kernel does not have audit
         * configured in and will let login proceed.  If we return EPERM
         * userspace will reject all logins.  This should be removed when we
         * support non init namespaces!!
         */
        if (current_user_ns() != &init_user_ns)
                return -ECONNREFUSED;

        switch (msg_type) {
        case AUDIT_LIST:
        case AUDIT_ADD:
        case AUDIT_DEL:
                return -EOPNOTSUPP;
        case AUDIT_GET:
        case AUDIT_SET:
        case AUDIT_GET_FEATURE:
        case AUDIT_SET_FEATURE:
        case AUDIT_LIST_RULES:
        case AUDIT_ADD_RULE:
        case AUDIT_DEL_RULE:
        case AUDIT_SIGNAL_INFO:
        case AUDIT_TTY_GET:
        case AUDIT_TTY_SET:
        case AUDIT_TRIM:
        case AUDIT_MAKE_EQUIV:
                /* Only support auditd and auditctl in initial pid namespace
                 * for now. */
                if (task_active_pid_ns(current) != &init_pid_ns)
                        return -EPERM;

                if (!netlink_capable(skb, CAP_AUDIT_CONTROL))
                        err = -EPERM;
                break;
        case AUDIT_USER:
        case AUDIT_FIRST_USER_MSG ... AUDIT_LAST_USER_MSG:
        case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2:
                if (!netlink_capable(skb, CAP_AUDIT_WRITE))
                        err = -EPERM;
                break;
        default:  /* bad msg */
                err = -EINVAL;
        }

        return err;
}

static void audit_log_common_recv_msg(struct audit_buffer **ab, u16 msg_type)
{
        uid_t uid = from_kuid(&init_user_ns, current_uid());
        pid_t pid = task_tgid_nr(current);

        if (!audit_enabled && msg_type != AUDIT_USER_AVC) {
                *ab = NULL;
                return;
        }

        *ab = audit_log_start(NULL, GFP_KERNEL, msg_type);
        if (unlikely(!*ab))
                return;
        audit_log_format(*ab, "pid=%d uid=%u", pid, uid);
        audit_log_session_info(*ab);
        audit_log_task_context(*ab);
}

int is_audit_feature_set(int i)
{
        return af.features & AUDIT_FEATURE_TO_MASK(i);
}


static int audit_get_feature(struct sk_buff *skb)
{
        u32 seq;

        seq = nlmsg_hdr(skb)->nlmsg_seq;

        audit_send_reply(skb, seq, AUDIT_GET_FEATURE, 0, 0, &af, sizeof(af));

        return 0;
}

static void audit_log_feature_change(int which, u32 old_feature, u32 new_feature,
                                     u32 old_lock, u32 new_lock, int res)
{
        struct audit_buffer *ab;

        if (audit_enabled == AUDIT_OFF)
                return;

        ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_FEATURE_CHANGE);
        audit_log_task_info(ab, current);
        audit_log_format(ab, " feature=%s old=%u new=%u old_lock=%u new_lock=%u res=%d",
                         audit_feature_names[which], !!old_feature, !!new_feature,
                         !!old_lock, !!new_lock, res);
        audit_log_end(ab);
}

static int audit_set_feature(struct sk_buff *skb)
{
        struct audit_features *uaf;
        int i;

        BUILD_BUG_ON(AUDIT_LAST_FEATURE + 1 > ARRAY_SIZE(audit_feature_names));
        uaf = nlmsg_data(nlmsg_hdr(skb));

        /* if there is ever a version 2 we should handle that here */

        for (i = 0; i <= AUDIT_LAST_FEATURE; i++) {
                u32 feature = AUDIT_FEATURE_TO_MASK(i);
                u32 old_feature, new_feature, old_lock, new_lock;

                /* if we are not changing this feature, move along */
                if (!(feature & uaf->mask))
                        continue;

                old_feature = af.features & feature;
                new_feature = uaf->features & feature;
                new_lock = (uaf->lock | af.lock) & feature;
                old_lock = af.lock & feature;

                /* are we changing a locked feature? */
                if (old_lock && (new_feature != old_feature)) {
                        audit_log_feature_change(i, old_feature, new_feature,
                                                 old_lock, new_lock, 0);
                        return -EPERM;
                }
        }
        /* nothing invalid, do the changes */
        for (i = 0; i <= AUDIT_LAST_FEATURE; i++) {
                u32 feature = AUDIT_FEATURE_TO_MASK(i);
                u32 old_feature, new_feature, old_lock, new_lock;

                /* if we are not changing this feature, move along */
                if (!(feature & uaf->mask))
                        continue;

                old_feature = af.features & feature;
                new_feature = uaf->features & feature;
                old_lock = af.lock & feature;
                new_lock = (uaf->lock | af.lock) & feature;

                if (new_feature != old_feature)
                        audit_log_feature_change(i, old_feature, new_feature,
                                                 old_lock, new_lock, 1);

                if (new_feature)
                        af.features |= feature;
                else
                        af.features &= ~feature;
                af.lock |= new_lock;
        }

        return 0;
}

static int audit_replace(pid_t pid)
{
        struct sk_buff *skb;

        skb = audit_make_reply(0, 0, AUDIT_REPLACE, 0, 0, &pid, sizeof(pid));
        if (!skb)
                return -ENOMEM;
        return auditd_send_unicast_skb(skb);
}

static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
{
        u32                     seq;
        void                    *data;
        int                     err;
        struct audit_buffer     *ab;
        u16                     msg_type = nlh->nlmsg_type;
        struct audit_sig_info   *sig_data;
        char                    *ctx = NULL;
        u32                     len;

        err = audit_netlink_ok(skb, msg_type);
        if (err)
                return err;

        seq  = nlh->nlmsg_seq;
        data = nlmsg_data(nlh);

        switch (msg_type) {
        case AUDIT_GET: {
                struct audit_status     s;
                memset(&s, 0, sizeof(s));
                s.enabled               = audit_enabled;
                s.failure               = audit_failure;
                rcu_read_lock();
                s.pid                   = auditd_conn.pid;
                rcu_read_unlock();
                s.rate_limit            = audit_rate_limit;
                s.backlog_limit         = audit_backlog_limit;
                s.lost                  = atomic_read(&audit_lost);
                s.backlog               = skb_queue_len(&audit_queue);
                s.feature_bitmap        = AUDIT_FEATURE_BITMAP_ALL;
                s.backlog_wait_time     = audit_backlog_wait_time;
                audit_send_reply(skb, seq, AUDIT_GET, 0, 0, &s, sizeof(s));
                break;
        }
        case AUDIT_SET: {
                struct audit_status     s;
                memset(&s, 0, sizeof(s));
                /* guard against past and future API changes */
                memcpy(&s, data, min_t(size_t, sizeof(s), nlmsg_len(nlh)));
                if (s.mask & AUDIT_STATUS_ENABLED) {
                        err = audit_set_enabled(s.enabled);
                        if (err < 0)
                                return err;
                }
                if (s.mask & AUDIT_STATUS_FAILURE) {
                        err = audit_set_failure(s.failure);
                        if (err < 0)
                                return err;
                }
                if (s.mask & AUDIT_STATUS_PID) {
                        /* NOTE: we are using task_tgid_vnr() below because
                         *       the s.pid value is relative to the namespace
                         *       of the caller; at present this doesn't matter
                         *       much since you can really only run auditd
                         *       from the initial pid namespace, but something
                         *       to keep in mind if this changes */
                        int new_pid = s.pid;
                        pid_t auditd_pid;
                        pid_t requesting_pid = task_tgid_vnr(current);

                        /* test the auditd connection */
                        audit_replace(requesting_pid);

                        rcu_read_lock();
                        auditd_pid = auditd_conn.pid;
                        /* only the current auditd can unregister itself */
                        if ((!new_pid) && (requesting_pid != auditd_pid)) {
                                rcu_read_unlock();
                                audit_log_config_change("audit_pid", new_pid,
                                                        auditd_pid, 0);
                                return -EACCES;
                        }
                        /* replacing a healthy auditd is not allowed */
                        if (auditd_pid && new_pid) {
                                rcu_read_unlock();
                                audit_log_config_change("audit_pid", new_pid,
                                                        auditd_pid, 0);
                                return -EEXIST;
                        }
                        rcu_read_unlock();

                        if (audit_enabled != AUDIT_OFF)
                                audit_log_config_change("audit_pid", new_pid,
                                                        auditd_pid, 1);

                        if (new_pid) {
                                /* register a new auditd connection */
                                auditd_set(new_pid,
                                           NETLINK_CB(skb).portid,
                                           sock_net(NETLINK_CB(skb).sk));
                                /* try to process any backlog */
                                wake_up_interruptible(&kauditd_wait);
                        } else
                                /* unregister the auditd connection */
                                auditd_reset();
                }
                if (s.mask & AUDIT_STATUS_RATE_LIMIT) {
                        err = audit_set_rate_limit(s.rate_limit);
                        if (err < 0)
                                return err;
                }
                if (s.mask & AUDIT_STATUS_BACKLOG_LIMIT) {
                        err = audit_set_backlog_limit(s.backlog_limit);
                        if (err < 0)
                                return err;
                }
                if (s.mask & AUDIT_STATUS_BACKLOG_WAIT_TIME) {
                        if (sizeof(s) > (size_t)nlh->nlmsg_len)
                                return -EINVAL;
                        if (s.backlog_wait_time > 10*AUDIT_BACKLOG_WAIT_TIME)
                                return -EINVAL;
                        err = audit_set_backlog_wait_time(s.backlog_wait_time);
                        if (err < 0)
                                return err;
                }
                if (s.mask == AUDIT_STATUS_LOST) {
                        u32 lost = atomic_xchg(&audit_lost, 0);

                        audit_log_config_change("lost", 0, lost, 1);
                        return lost;
                }
                break;
        }
        case AUDIT_GET_FEATURE:
                err = audit_get_feature(skb);
                if (err)
                        return err;
                break;
        case AUDIT_SET_FEATURE:
                err = audit_set_feature(skb);
                if (err)
                        return err;
                break;
        case AUDIT_USER:
        case AUDIT_FIRST_USER_MSG ... AUDIT_LAST_USER_MSG:
        case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2:
                if (!audit_enabled && msg_type != AUDIT_USER_AVC)
                        return 0;

                err = audit_filter(msg_type, AUDIT_FILTER_USER);
                if (err == 1) { /* match or error */
                        err = 0;
                        if (msg_type == AUDIT_USER_TTY) {
                                err = tty_audit_push();
                                if (err)
                                        break;
                        }
                        audit_log_common_recv_msg(&ab, msg_type);
                        if (msg_type != AUDIT_USER_TTY)
                                audit_log_format(ab, " msg='%.*s'",
                                                 AUDIT_MESSAGE_TEXT_MAX,
                                                 (char *)data);
                        else {
                                int size;

                                audit_log_format(ab, " data=");
                                size = nlmsg_len(nlh);
                                if (size > 0 &&
                                    ((unsigned char *)data)[size - 1] == '\0')
                                        size--;
                                audit_log_n_untrustedstring(ab, data, size);
                        }
                        audit_set_portid(ab, NETLINK_CB(skb).portid);
                        audit_log_end(ab);
                }
                break;
        case AUDIT_ADD_RULE:
        case AUDIT_DEL_RULE:
                if (nlmsg_len(nlh) < sizeof(struct audit_rule_data))
                        return -EINVAL;
                if (audit_enabled == AUDIT_LOCKED) {
                        audit_log_common_recv_msg(&ab, AUDIT_CONFIG_CHANGE);
                        audit_log_format(ab, " audit_enabled=%d res=0", audit_enabled);
                        audit_log_end(ab);
                        return -EPERM;
                }
                err = audit_rule_change(msg_type, NETLINK_CB(skb).portid,
                                           seq, data, nlmsg_len(nlh));
                break;
        case AUDIT_LIST_RULES:
                err = audit_list_rules_send(skb, seq);
                break;
        case AUDIT_TRIM:
                audit_trim_trees();
                audit_log_common_recv_msg(&ab, AUDIT_CONFIG_CHANGE);
                audit_log_format(ab, " op=trim res=1");
                audit_log_end(ab);
                break;
        case AUDIT_MAKE_EQUIV: {
                void *bufp = data;
                u32 sizes[2];
                size_t msglen = nlmsg_len(nlh);
                char *old, *new;

                err = -EINVAL;
                if (msglen < 2 * sizeof(u32))
                        break;
                memcpy(sizes, bufp, 2 * sizeof(u32));
                bufp += 2 * sizeof(u32);
                msglen -= 2 * sizeof(u32);
                old = audit_unpack_string(&bufp, &msglen, sizes[0]);
                if (IS_ERR(old)) {
                        err = PTR_ERR(old);
                        break;
                }
                new = audit_unpack_string(&bufp, &msglen, sizes[1]);
                if (IS_ERR(new)) {
                        err = PTR_ERR(new);
                        kfree(old);
                        break;
                }
                /* OK, here comes... */
                err = audit_tag_tree(old, new);

                audit_log_common_recv_msg(&ab, AUDIT_CONFIG_CHANGE);

                audit_log_format(ab, " op=make_equiv old=");
                audit_log_untrustedstring(ab, old);
                audit_log_format(ab, " new=");
                audit_log_untrustedstring(ab, new);
                audit_log_format(ab, " res=%d", !err);
                audit_log_end(ab);
                kfree(old);
                kfree(new);
                break;
        }
        case AUDIT_SIGNAL_INFO:
                len = 0;
                if (audit_sig_sid) {
                        err = security_secid_to_secctx(audit_sig_sid, &ctx, &len);
                        if (err)
                                return err;
                }
                sig_data = kmalloc(sizeof(*sig_data) + len, GFP_KERNEL);
                if (!sig_data) {
                        if (audit_sig_sid)
                                security_release_secctx(ctx, len);
                        return -ENOMEM;
                }
                sig_data->uid = from_kuid(&init_user_ns, audit_sig_uid);
                sig_data->pid = audit_sig_pid;
                if (audit_sig_sid) {
                        memcpy(sig_data->ctx, ctx, len);
                        security_release_secctx(ctx, len);
                }
                audit_send_reply(skb, seq, AUDIT_SIGNAL_INFO, 0, 0,
                                 sig_data, sizeof(*sig_data) + len);
                kfree(sig_data);
                break;
        case AUDIT_TTY_GET: {
                struct audit_tty_status s;
                unsigned int t;

                t = READ_ONCE(current->signal->audit_tty);
                s.enabled = t & AUDIT_TTY_ENABLE;
                s.log_passwd = !!(t & AUDIT_TTY_LOG_PASSWD);

                audit_send_reply(skb, seq, AUDIT_TTY_GET, 0, 0, &s, sizeof(s));
                break;
        }
        case AUDIT_TTY_SET: {
                struct audit_tty_status s, old;
                struct audit_buffer     *ab;
                unsigned int t;

                memset(&s, 0, sizeof(s));
                /* guard against past and future API changes */
                memcpy(&s, data, min_t(size_t, sizeof(s), nlmsg_len(nlh)));
                /* check if new data is valid */
                if ((s.enabled != 0 && s.enabled != 1) ||
                    (s.log_passwd != 0 && s.log_passwd != 1))
                        err = -EINVAL;

                if (err)
                        t = READ_ONCE(current->signal->audit_tty);
                else {
                        t = s.enabled | (-s.log_passwd & AUDIT_TTY_LOG_PASSWD);
                        t = xchg(&current->signal->audit_tty, t);
                }
                old.enabled = t & AUDIT_TTY_ENABLE;
                old.log_passwd = !!(t & AUDIT_TTY_LOG_PASSWD);

                audit_log_common_recv_msg(&ab, AUDIT_CONFIG_CHANGE);
                audit_log_format(ab, " op=tty_set old-enabled=%d new-enabled=%d"
                                 " old-log_passwd=%d new-log_passwd=%d res=%d",
                                 old.enabled, s.enabled, old.log_passwd,
                                 s.log_passwd, !err);
                audit_log_end(ab);
                break;
        }
        default:
                err = -EINVAL;
                break;
        }

        return err < 0 ? err : 0;
}

/*
 * Get message from skb.  Each message is processed by audit_receive_msg.
 * Malformed skbs with wrong length are discarded silently.
 */
static void audit_receive_skb(struct sk_buff *skb)
{
        struct nlmsghdr *nlh;
        /*
         * len MUST be signed for nlmsg_next to be able to dec it below 0
         * if the nlmsg_len was not aligned
         */
        int len;
        int err;

        nlh = nlmsg_hdr(skb);
        len = skb->len;

        while (nlmsg_ok(nlh, len)) {
                err = audit_receive_msg(skb, nlh);
                /* if err or if this message says it wants a response */
                if (err || (nlh->nlmsg_flags & NLM_F_ACK))
                        netlink_ack(skb, nlh, err);

                nlh = nlmsg_next(nlh, &len);
        }
}

/* Receive messages from netlink socket. */
static void audit_receive(struct sk_buff  *skb)
{
        mutex_lock(&audit_cmd_mutex);
        audit_receive_skb(skb);
        mutex_unlock(&audit_cmd_mutex);
}

/* Run custom bind function on netlink socket group connect or bind requests. */
static int audit_bind(struct net *net, int group)
{
        if (!capable(CAP_AUDIT_READ))
                return -EPERM;

        return 0;
}

static int __net_init audit_net_init(struct net *net)
{
        struct netlink_kernel_cfg cfg = {
                .input  = audit_receive,
                .bind   = audit_bind,
                .flags  = NL_CFG_F_NONROOT_RECV,
                .groups = AUDIT_NLGRP_MAX,
        };

        struct audit_net *aunet = net_generic(net, audit_net_id);

        aunet->sk = netlink_kernel_create(net, NETLINK_AUDIT, &cfg);
        if (aunet->sk == NULL) {
                audit_panic("cannot initialize netlink socket in namespace");
                return -ENOMEM;
        }
        aunet->sk->sk_sndtimeo = MAX_SCHEDULE_TIMEOUT;

        return 0;
}

static void __net_exit audit_net_exit(struct net *net)
{
        struct audit_net *aunet = net_generic(net, audit_net_id);

        rcu_read_lock();
        if (net == auditd_conn.net)
                auditd_reset();
        rcu_read_unlock();

        netlink_kernel_release(aunet->sk);
}

static struct pernet_operations audit_net_ops __net_initdata = {
        .init = audit_net_init,
        .exit = audit_net_exit,
        .id = &audit_net_id,
        .size = sizeof(struct audit_net),
};

/* Initialize audit support at boot time. */
static int __init audit_init(void)
{
        int i;

        if (audit_initialized == AUDIT_DISABLED)
                return 0;

        memset(&auditd_conn, 0, sizeof(auditd_conn));
        spin_lock_init(&auditd_conn.lock);

        skb_queue_head_init(&audit_queue);
        skb_queue_head_init(&audit_retry_queue);
        skb_queue_head_init(&audit_hold_queue);

        for (i = 0; i < AUDIT_INODE_BUCKETS; i++)
                INIT_LIST_HEAD(&audit_inode_hash[i]);

        pr_info("initializing netlink subsys (%s)\n",
                audit_default ? "enabled" : "disabled");
        register_pernet_subsys(&audit_net_ops);

        audit_initialized = AUDIT_INITIALIZED;
        audit_enabled = audit_default;
        audit_ever_enabled |= !!audit_default;

        kauditd_task = kthread_run(kauditd_thread, NULL, "kauditd");
        if (IS_ERR(kauditd_task)) {
                int err = PTR_ERR(kauditd_task);
                panic("audit: failed to start the kauditd thread (%d)\n", err);
        }

        audit_log(NULL, GFP_KERNEL, AUDIT_KERNEL,
                "state=initialized audit_enabled=%u res=1",
                 audit_enabled);

        return 0;
}
__initcall(audit_init);

/* Process kernel command-line parameter at boot time.  audit=0 or audit=1. */
static int __init audit_enable(char *str)
{
        audit_default = !!simple_strtol(str, NULL, 0);
        if (!audit_default)
                audit_initialized = AUDIT_DISABLED;

        pr_info("%s\n", audit_default ?
                "enabled (after initialization)" : "disabled (until reboot)");

        return 1;
}
__setup("audit=", audit_enable);

/* Process kernel command-line parameter at boot time.
 * audit_backlog_limit=<n> */
static int __init audit_backlog_limit_set(char *str)
{
        u32 audit_backlog_limit_arg;

        pr_info("audit_backlog_limit: ");
        if (kstrtouint(str, 0, &audit_backlog_limit_arg)) {
                pr_cont("using default of %u, unable to parse %s\n",
                        audit_backlog_limit, str);
                return 1;
        }

        audit_backlog_limit = audit_backlog_limit_arg;
        pr_cont("%d\n", audit_backlog_limit);

        return 1;
}
__setup("audit_backlog_limit=", audit_backlog_limit_set);

static void audit_buffer_free(struct audit_buffer *ab)
{
        unsigned long flags;

        if (!ab)
                return;

        kfree_skb(ab->skb);
        spin_lock_irqsave(&audit_freelist_lock, flags);
        if (audit_freelist_count > AUDIT_MAXFREE)
                kfree(ab);
        else {
                audit_freelist_count++;
                list_add(&ab->list, &audit_freelist);
        }
        spin_unlock_irqrestore(&audit_freelist_lock, flags);
}

static struct audit_buffer * audit_buffer_alloc(struct audit_context *ctx,
                                                gfp_t gfp_mask, int type)
{
        unsigned long flags;
        struct audit_buffer *ab = NULL;
        struct nlmsghdr *nlh;

        spin_lock_irqsave(&audit_freelist_lock, flags);
        if (!list_empty(&audit_freelist)) {
                ab = list_entry(audit_freelist.next,
                                struct audit_buffer, list);
                list_del(&ab->list);
                --audit_freelist_count;
        }
        spin_unlock_irqrestore(&audit_freelist_lock, flags);

        if (!ab) {
                ab = kmalloc(sizeof(*ab), gfp_mask);
                if (!ab)
                        goto err;
        }

        ab->ctx = ctx;
        ab->gfp_mask = gfp_mask;

        ab->skb = nlmsg_new(AUDIT_BUFSIZ, gfp_mask);
        if (!ab->skb)
                goto err;

        nlh = nlmsg_put(ab->skb, 0, 0, type, 0, 0);
        if (!nlh)
                goto out_kfree_skb;

        return ab;

out_kfree_skb:
        kfree_skb(ab->skb);
        ab->skb = NULL;
err:
        audit_buffer_free(ab);
        return NULL;
}

/**
 * audit_serial - compute a serial number for the audit record
 *
 * Compute a serial number for the audit record.  Audit records are
 * written to user-space as soon as they are generated, so a complete
 * audit record may be written in several pieces.  The timestamp of the
 * record and this serial number are used by the user-space tools to
 * determine which pieces belong to the same audit record.  The
 * (timestamp,serial) tuple is unique for each syscall and is live from
 * syscall entry to syscall exit.
 *
 * NOTE: Another possibility is to store the formatted records off the
 * audit context (for those records that have a context), and emit them
 * all at syscall exit.  However, this could delay the reporting of
 * significant errors until syscall exit (or never, if the system
 * halts).
 */
unsigned int audit_serial(void)
{
        static atomic_t serial = ATOMIC_INIT(0);

        return atomic_add_return(1, &serial);
}

static inline void audit_get_stamp(struct audit_context *ctx,
                                   struct timespec *t, unsigned int *serial)
{
        if (!ctx || !auditsc_get_stamp(ctx, t, serial)) {
                *t = CURRENT_TIME;
                *serial = audit_serial();
        }
}

/**
 * audit_log_start - obtain an audit buffer
 * @ctx: audit_context (may be NULL)
 * @gfp_mask: type of allocation
 * @type: audit message type
 *
 * Returns audit_buffer pointer on success or NULL on error.
 *
 * Obtain an audit buffer.  This routine does locking to obtain the
 * audit buffer, but then no locking is required for calls to
 * audit_log_*format.  If the task (ctx) is a task that is currently in a
 * syscall, then the syscall is marked as auditable and an audit record
 * will be written at syscall exit.  If there is no associated task, then
 * task context (ctx) should be NULL.
 */
struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
                                     int type)
{
        struct audit_buffer *ab;
        struct timespec t;
        unsigned int uninitialized_var(serial);

        if (audit_initialized != AUDIT_INITIALIZED)
                return NULL;

        if (unlikely(!audit_filter(type, AUDIT_FILTER_TYPE)))
                return NULL;

        /* NOTE: don't ever fail/sleep on these two conditions:
         * 1. auditd generated record - since we need auditd to drain the
         *    queue; also, when we are checking for auditd, compare PIDs using
         *    task_tgid_vnr() since auditd_pid is set in audit_receive_msg()
         *    using a PID anchored in the caller's namespace
         * 2. generator holding the audit_cmd_mutex - we don't want to block
         *    while holding the mutex */
        if (!(auditd_test_task(current) ||
              (current == __mutex_owner(&audit_cmd_mutex)))) {
                long stime = audit_backlog_wait_time;

                while (audit_backlog_limit &&
                       (skb_queue_len(&audit_queue) > audit_backlog_limit)) {
                        /* wake kauditd to try and flush the queue */
                        wake_up_interruptible(&kauditd_wait);

                        /* sleep if we are allowed and we haven't exhausted our
                         * backlog wait limit */
                        if (gfpflags_allow_blocking(gfp_mask) && (stime > 0)) {
                                DECLARE_WAITQUEUE(wait, current);

                                add_wait_queue_exclusive(&audit_backlog_wait,
                                                         &wait);
                                set_current_state(TASK_UNINTERRUPTIBLE);
                                stime = schedule_timeout(stime);
                                remove_wait_queue(&audit_backlog_wait, &wait);
                        } else {
                                if (audit_rate_check() && printk_ratelimit())
                                        pr_warn("audit_backlog=%d > audit_backlog_limit=%d\n",
                                                skb_queue_len(&audit_queue),
                                                audit_backlog_limit);
                                audit_log_lost("backlog limit exceeded");
                                return NULL;
                        }
                }
        }

        ab = audit_buffer_alloc(ctx, gfp_mask, type);
        if (!ab) {
                audit_log_lost("out of memory in audit_log_start");
                return NULL;
        }

        audit_get_stamp(ab->ctx, &t, &serial);
        audit_log_format(ab, "audit(%lu.%03lu:%u): ",
                         t.tv_sec, t.tv_nsec/1000000, serial);

        return ab;
}

/**
 * audit_expand - expand skb in the audit buffer
 * @ab: audit_buffer
 * @extra: space to add at tail of the skb
 *
 * Returns 0 (no space) on failed expansion, or available space if
 * successful.
 */
static inline int audit_expand(struct audit_buffer *ab, int extra)
{
        struct sk_buff *skb = ab->skb;
        int oldtail = skb_tailroom(skb);
        int ret = pskb_expand_head(skb, 0, extra, ab->gfp_mask);
        int newtail = skb_tailroom(skb);

        if (ret < 0) {
                audit_log_lost("out of memory in audit_expand");
                return 0;
        }

        skb->truesize += newtail - oldtail;
        return newtail;
}

/*
 * Format an audit message into the audit buffer.  If there isn't enough
 * room in the audit buffer, more room will be allocated and vsnprint
 * will be called a second time.  Currently, we assume that a printk
 * can't format message larger than 1024 bytes, so we don't either.
 */
static void audit_log_vformat(struct audit_buffer *ab, const char *fmt,
                              va_list args)
{
        int len, avail;
        struct sk_buff *skb;
        va_list args2;

        if (!ab)
                return;

        BUG_ON(!ab->skb);
        skb = ab->skb;
        avail = skb_tailroom(skb);
        if (avail == 0) {
                avail = audit_expand(ab, AUDIT_BUFSIZ);
                if (!avail)
                        goto out;
        }
        va_copy(args2, args);
        len = vsnprintf(skb_tail_pointer(skb), avail, fmt, args);
        if (len >= avail) {
                /* The printk buffer is 1024 bytes long, so if we get
                 * here and AUDIT_BUFSIZ is at least 1024, then we can
                 * log everything that printk could have logged. */
                avail = audit_expand(ab,
                        max_t(unsigned, AUDIT_BUFSIZ, 1+len-avail));
                if (!avail)
                        goto out_va_end;
                len = vsnprintf(skb_tail_pointer(skb), avail, fmt, args2);
        }
        if (len > 0)
                skb_put(skb, len);
out_va_end:
        va_end(args2);
out:
        return;
}

/**
 * audit_log_format - format a message into the audit buffer.
 * @ab: audit_buffer
 * @fmt: format string
 * @...: optional parameters matching @fmt string
 *
 * All the work is done in audit_log_vformat.
 */
void audit_log_format(struct audit_buffer *ab, const char *fmt, ...)
{
        va_list args;

        if (!ab)
                return;
        va_start(args, fmt);
        audit_log_vformat(ab, fmt, args);
        va_end(args);
}

/**
 * audit_log_hex - convert a buffer to hex and append it to the audit skb
 * @ab: the audit_buffer
 * @buf: buffer to convert to hex
 * @len: length of @buf to be converted
 *
 * No return value; failure to expand is silently ignored.
 *
 * This function will take the passed buf and convert it into a string of
 * ascii hex digits. The new string is placed onto the skb.
 */
void audit_log_n_hex(struct audit_buffer *ab, const unsigned char *buf,
                size_t len)
{
        int i, avail, new_len;
        unsigned char *ptr;
        struct sk_buff *skb;

        if (!ab)
                return;

        BUG_ON(!ab->skb);
        skb = ab->skb;
        avail = skb_tailroom(skb);
        new_len = len<<1;
        if (new_len >= avail) {
                /* Round the buffer request up to the next multiple */
                new_len = AUDIT_BUFSIZ*(((new_len-avail)/AUDIT_BUFSIZ) + 1);
                avail = audit_expand(ab, new_len);
                if (!avail)
                        return;
        }

        ptr = skb_tail_pointer(skb);
        for (i = 0; i < len; i++)
                ptr = hex_byte_pack_upper(ptr, buf[i]);
        *ptr = 0;
        skb_put(skb, len << 1); /* new string is twice the old string */
}

/*
 * Format a string of no more than slen characters into the audit buffer,
 * enclosed in quote marks.
 */
void audit_log_n_string(struct audit_buffer *ab, const char *string,
                        size_t slen)
{
        int avail, new_len;
        unsigned char *ptr;
        struct sk_buff *skb;

        if (!ab)
                return;

        BUG_ON(!ab->skb);
        skb = ab->skb;
        avail = skb_tailroom(skb);
        new_len = slen + 3;     /* enclosing quotes + null terminator */
        if (new_len > avail) {
                avail = audit_expand(ab, new_len);
                if (!avail)
                        return;
        }
        ptr = skb_tail_pointer(skb);
        *ptr++ = '"';
        memcpy(ptr, string, slen);
        ptr += slen;
        *ptr++ = '"';
        *ptr = 0;
        skb_put(skb, slen + 2); /* don't include null terminator */
}

/**
 * audit_string_contains_control - does a string need to be logged in hex
 * @string: string to be checked
 * @len: max length of the string to check
 */
bool audit_string_contains_control(const char *string, size_t len)
{
        const unsigned char *p;
        for (p = string; p < (const unsigned char *)string + len; p++) {
                if (*p == '"' || *p < 0x21 || *p > 0x7e)
                        return true;
        }
        return false;
}

/**
 * audit_log_n_untrustedstring - log a string that may contain random characters
 * @ab: audit_buffer
 * @len: length of string (not including trailing null)
 * @string: string to be logged
 *
 * This code will escape a string that is passed to it if the string
 * contains a control character, unprintable character, double quote mark,
 * or a space. Unescaped strings will start and end with a double quote mark.
 * Strings that are escaped are printed in hex (2 digits per char).
 *
 * The caller specifies the number of characters in the string to log, which may
 * or may not be the entire string.
 */
void audit_log_n_untrustedstring(struct audit_buffer *ab, const char *string,
                                 size_t len)
{
        if (audit_string_contains_control(string, len))
                audit_log_n_hex(ab, string, len);
        else
                audit_log_n_string(ab, string, len);
}

/**
 * audit_log_untrustedstring - log a string that may contain random characters
 * @ab: audit_buffer
 * @string: string to be logged
 *
 * Same as audit_log_n_untrustedstring(), except that strlen is used to
 * determine string length.
 */
void audit_log_untrustedstring(struct audit_buffer *ab, const char *string)
{
        audit_log_n_untrustedstring(ab, string, strlen(string));
}

/* This is a helper-function to print the escaped d_path */
void audit_log_d_path(struct audit_buffer *ab, const char *prefix,
                      const struct path *path)
{
        char *p, *pathname;

        if (prefix)
                audit_log_format(ab, "%s", prefix);

        /* We will allow 11 spaces for ' (deleted)' to be appended */
        pathname = kmalloc(PATH_MAX+11, ab->gfp_mask);
        if (!pathname) {
                audit_log_string(ab, "<no_memory>");
                return;
        }
        p = d_path(path, pathname, PATH_MAX+11);
        if (IS_ERR(p)) { /* Should never happen since we send PATH_MAX */
                /* FIXME: can we save some information here? */
                audit_log_string(ab, "<too_long>");
        } else
                audit_log_untrustedstring(ab, p);
        kfree(pathname);
}

void audit_log_session_info(struct audit_buffer *ab)
{
        unsigned int sessionid = audit_get_sessionid(current);
        uid_t auid = from_kuid(&init_user_ns, audit_get_loginuid(current));

        audit_log_format(ab, " auid=%u ses=%u", auid, sessionid);
}

void audit_log_key(struct audit_buffer *ab, char *key)
{
        audit_log_format(ab, " key=");
        if (key)
                audit_log_untrustedstring(ab, key);
        else
                audit_log_format(ab, "(null)");
}

void audit_log_cap(struct audit_buffer *ab, char *prefix, kernel_cap_t *cap)
{
        int i;

        audit_log_format(ab, " %s=", prefix);
        CAP_FOR_EACH_U32(i) {
                audit_log_format(ab, "%08x",
                                 cap->cap[CAP_LAST_U32 - i]);
        }
}

static void audit_log_fcaps(struct audit_buffer *ab, struct audit_names *name)
{
        kernel_cap_t *perm = &name->fcap.permitted;
        kernel_cap_t *inh = &name->fcap.inheritable;
        int log = 0;

        if (!cap_isclear(*perm)) {
                audit_log_cap(ab, "cap_fp", perm);
                log = 1;
        }
        if (!cap_isclear(*inh)) {
                audit_log_cap(ab, "cap_fi", inh);
                log = 1;
        }

        if (log)
                audit_log_format(ab, " cap_fe=%d cap_fver=%x",
                                 name->fcap.fE, name->fcap_ver);
}

static inline int audit_copy_fcaps(struct audit_names *name,
                                   const struct dentry *dentry)
{
        struct cpu_vfs_cap_data caps;
        int rc;

        if (!dentry)
                return 0;

        rc = get_vfs_caps_from_disk(dentry, &caps);
        if (rc)
                return rc;

        name->fcap.permitted = caps.permitted;
        name->fcap.inheritable = caps.inheritable;
        name->fcap.fE = !!(caps.magic_etc & VFS_CAP_FLAGS_EFFECTIVE);
        name->fcap_ver = (caps.magic_etc & VFS_CAP_REVISION_MASK) >>
                                VFS_CAP_REVISION_SHIFT;

        return 0;
}

/* Copy inode data into an audit_names. */
void audit_copy_inode(struct audit_names *name, const struct dentry *dentry,
                      struct inode *inode)
{
        name->ino   = inode->i_ino;
        name->dev   = inode->i_sb->s_dev;
        name->mode  = inode->i_mode;
        name->uid   = inode->i_uid;
        name->gid   = inode->i_gid;
        name->rdev  = inode->i_rdev;
        security_inode_getsecid(inode, &name->osid);
        audit_copy_fcaps(name, dentry);
}

/**
 * audit_log_name - produce AUDIT_PATH record from struct audit_names
 * @context: audit_context for the task
 * @n: audit_names structure with reportable details
 * @path: optional path to report instead of audit_names->name
 * @record_num: record number to report when handling a list of names
 * @call_panic: optional pointer to int that will be updated if secid fails
 */
void audit_log_name(struct audit_context *context, struct audit_names *n,
                    const struct path *path, int record_num, int *call_panic)
{
        struct audit_buffer *ab;
        ab = audit_log_start(context, GFP_KERNEL, AUDIT_PATH);
        if (!ab)
                return;

        audit_log_format(ab, "item=%d", record_num);

        if (path)
                audit_log_d_path(ab, " name=", path);
        else if (n->name) {
                switch (n->name_len) {
                case AUDIT_NAME_FULL:
                        /* log the full path */
                        audit_log_format(ab, " name=");
                        audit_log_untrustedstring(ab, n->name->name);
                        break;
                case 0:
                        /* name was specified as a relative path and the
                         * directory component is the cwd */
                        audit_log_d_path(ab, " name=", &context->pwd);
                        break;
                default:
                        /* log the name's directory component */
                        audit_log_format(ab, " name=");
                        audit_log_n_untrustedstring(ab, n->name->name,
                                                    n->name_len);
                }
        } else
                audit_log_format(ab, " name=(null)");

        if (n->ino != AUDIT_INO_UNSET)
                audit_log_format(ab, " inode=%lu"
                                 " dev=%02x:%02x mode=%#ho"
                                 " ouid=%u ogid=%u rdev=%02x:%02x",
                                 n->ino,
                                 MAJOR(n->dev),
                                 MINOR(n->dev),
                                 n->mode,
                                 from_kuid(&init_user_ns, n->uid),
                                 from_kgid(&init_user_ns, n->gid),
                                 MAJOR(n->rdev),
                                 MINOR(n->rdev));
        if (n->osid != 0) {
                char *ctx = NULL;
                u32 len;
                if (security_secid_to_secctx(
                        n->osid, &ctx, &len)) {
                        audit_log_format(ab, " osid=%u", n->osid);
                        if (call_panic)
                                *call_panic = 2;
                } else {
                        audit_log_format(ab, " obj=%s", ctx);
                        security_release_secctx(ctx, len);
                }
        }

        /* log the audit_names record type */
        audit_log_format(ab, " nametype=");
        switch(n->type) {
        case AUDIT_TYPE_NORMAL:
                audit_log_format(ab, "NORMAL");
                break;
        case AUDIT_TYPE_PARENT:
                audit_log_format(ab, "PARENT");
                break;
        case AUDIT_TYPE_CHILD_DELETE:
                audit_log_format(ab, "DELETE");
                break;
        case AUDIT_TYPE_CHILD_CREATE:
                audit_log_format(ab, "CREATE");
                break;
        default:
                audit_log_format(ab, "UNKNOWN");
                break;
        }

        audit_log_fcaps(ab, n);
        audit_log_end(ab);
}

int audit_log_task_context(struct audit_buffer *ab)
{
        char *ctx = NULL;
        unsigned len;
        int error;
        u32 sid;

        security_task_getsecid(current, &sid);
        if (!sid)
                return 0;

        error = security_secid_to_secctx(sid, &ctx, &len);
        if (error) {
                if (error != -EINVAL)
                        goto error_path;
                return 0;
        }

        audit_log_format(ab, " subj=%s", ctx);
        security_release_secctx(ctx, len);
        return 0;

error_path:
        audit_panic("error in audit_log_task_context");
        return error;
}
EXPORT_SYMBOL(audit_log_task_context);

void audit_log_d_path_exe(struct audit_buffer *ab,
                          struct mm_struct *mm)
{
        struct file *exe_file;

        if (!mm)
                goto out_null;

        exe_file = get_mm_exe_file(mm);
        if (!exe_file)
                goto out_null;

        audit_log_d_path(ab, " exe=", &exe_file->f_path);
        fput(exe_file);
        return;
out_null:
        audit_log_format(ab, " exe=(null)");
}

struct tty_struct *audit_get_tty(struct task_struct *tsk)
{
        struct tty_struct *tty = NULL;
        unsigned long flags;

        spin_lock_irqsave(&tsk->sighand->siglock, flags);
        if (tsk->signal)
                tty = tty_kref_get(tsk->signal->tty);
        spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
        return tty;
}

void audit_put_tty(struct tty_struct *tty)
{
        tty_kref_put(tty);
}

void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
{
        const struct cred *cred;
        char comm[sizeof(tsk->comm)];
        struct tty_struct *tty;

        if (!ab)
                return;

        /* tsk == current */
        cred = current_cred();
        tty = audit_get_tty(tsk);
        audit_log_format(ab,
                         " ppid=%d pid=%d auid=%u uid=%u gid=%u"
                         " euid=%u suid=%u fsuid=%u"
                         " egid=%u sgid=%u fsgid=%u tty=%s ses=%u",
                         task_ppid_nr(tsk),
                         task_tgid_nr(tsk),
                         from_kuid(&init_user_ns, audit_get_loginuid(tsk)),
                         from_kuid(&init_user_ns, cred->uid),
                         from_kgid(&init_user_ns, cred->gid),
                         from_kuid(&init_user_ns, cred->euid),
                         from_kuid(&init_user_ns, cred->suid),
                         from_kuid(&init_user_ns, cred->fsuid),
                         from_kgid(&init_user_ns, cred->egid),
                         from_kgid(&init_user_ns, cred->sgid),
                         from_kgid(&init_user_ns, cred->fsgid),
                         tty ? tty_name(tty) : "(none)",
                         audit_get_sessionid(tsk));
        audit_put_tty(tty);
        audit_log_format(ab, " comm=");
        audit_log_untrustedstring(ab, get_task_comm(comm, tsk));
        audit_log_d_path_exe(ab, tsk->mm);
        audit_log_task_context(ab);
}
EXPORT_SYMBOL(audit_log_task_info);

/**
 * audit_log_link_denied - report a link restriction denial
 * @operation: specific link operation
 * @link: the path that triggered the restriction
 */
void audit_log_link_denied(const char *operation, const struct path *link)
{
        struct audit_buffer *ab;
        struct audit_names *name;

        name = kzalloc(sizeof(*name), GFP_NOFS);
        if (!name)
                return;

        /* Generate AUDIT_ANOM_LINK with subject, operation, outcome. */
        ab = audit_log_start(current->audit_context, GFP_KERNEL,
                             AUDIT_ANOM_LINK);
        if (!ab)
                goto out;
        audit_log_format(ab, "op=%s", operation);
        audit_log_task_info(ab, current);
        audit_log_format(ab, " res=0");
        audit_log_end(ab);

        /* Generate AUDIT_PATH record with object. */
        name->type = AUDIT_TYPE_NORMAL;
        audit_copy_inode(name, link->dentry, d_backing_inode(link->dentry));
        audit_log_name(current->audit_context, name, link, 0, NULL);
out:
        kfree(name);
}

/**
 * audit_log_end - end one audit record
 * @ab: the audit_buffer
 *
 * We can not do a netlink send inside an irq context because it blocks (last
 * arg, flags, is not set to MSG_DONTWAIT), so the audit buffer is placed on a
 * queue and a tasklet is scheduled to remove them from the queue outside the
 * irq context.  May be called in any context.
 */
void audit_log_end(struct audit_buffer *ab)
{
        struct sk_buff *skb;
        struct nlmsghdr *nlh;

        if (!ab)
                return;

        if (audit_rate_check()) {
                skb = ab->skb;
                ab->skb = NULL;

                /* setup the netlink header, see the comments in
                 * kauditd_send_multicast_skb() for length quirks */
                nlh = nlmsg_hdr(skb);
                nlh->nlmsg_len = skb->len - NLMSG_HDRLEN;

                /* queue the netlink packet and poke the kauditd thread */
                skb_queue_tail(&audit_queue, skb);
                wake_up_interruptible(&kauditd_wait);
        } else
                audit_log_lost("rate limit exceeded");

        audit_buffer_free(ab);
}

/**
 * audit_log - Log an audit record
 * @ctx: audit context
 * @gfp_mask: type of allocation
 * @type: audit message type
 * @fmt: format string to use
 * @...: variable parameters matching the format string
 *
 * This is a convenience function that calls audit_log_start,
 * audit_log_vformat, and audit_log_end.  It may be called
 * in any context.
 */
void audit_log(struct audit_context *ctx, gfp_t gfp_mask, int type,
               const char *fmt, ...)
{
        struct audit_buffer *ab;
        va_list args;

        ab = audit_log_start(ctx, gfp_mask, type);
        if (ab) {
                va_start(args, fmt);
                audit_log_vformat(ab, fmt, args);
                va_end(args);
                audit_log_end(ab);
        }
}

#ifdef CONFIG_SECURITY
/**
 * audit_log_secctx - Converts and logs SELinux context
 * @ab: audit_buffer
 * @secid: security number
 *
 * This is a helper function that calls security_secid_to_secctx to convert
 * secid to secctx and then adds the (converted) SELinux context to the audit
 * log by calling audit_log_format, thus also preventing leak of internal secid
 * to userspace. If secid cannot be converted audit_panic is called.
 */
void audit_log_secctx(struct audit_buffer *ab, u32 secid)
{
        u32 len;
        char *secctx;

        if (security_secid_to_secctx(secid, &secctx, &len)) {
                audit_panic("Cannot convert secid to context");
        } else {
                audit_log_format(ab, " obj=%s", secctx);
                security_release_secctx(secctx, len);
        }
}
EXPORT_SYMBOL(audit_log_secctx);
#endif

EXPORT_SYMBOL(audit_log_start);
EXPORT_SYMBOL(audit_log_end);
EXPORT_SYMBOL(audit_log_format);
EXPORT_SYMBOL(audit_log);