KEYS: return full count in keyring_read() if buffer is too small

[sfrench/cifs-2.6.git] / security / keys / keyring.c

/* Keyring handling
 *
 * Copyright (C) 2004-2005, 2008, 2013 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * 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.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/security.h>
#include <linux/seq_file.h>
#include <linux/err.h>
#include <keys/keyring-type.h>
#include <keys/user-type.h>
#include <linux/assoc_array_priv.h>
#include <linux/uaccess.h>
#include "internal.h"

/*
 * When plumbing the depths of the key tree, this sets a hard limit
 * set on how deep we're willing to go.
 */
#define KEYRING_SEARCH_MAX_DEPTH 6

/*
 * We keep all named keyrings in a hash to speed looking them up.
 */
#define KEYRING_NAME_HASH_SIZE  (1 << 5)

/*
 * We mark pointers we pass to the associative array with bit 1 set if
 * they're keyrings and clear otherwise.
 */
#define KEYRING_PTR_SUBTYPE     0x2UL

static inline bool keyring_ptr_is_keyring(const struct assoc_array_ptr *x)
{
        return (unsigned long)x & KEYRING_PTR_SUBTYPE;
}
static inline struct key *keyring_ptr_to_key(const struct assoc_array_ptr *x)
{
        void *object = assoc_array_ptr_to_leaf(x);
        return (struct key *)((unsigned long)object & ~KEYRING_PTR_SUBTYPE);
}
static inline void *keyring_key_to_ptr(struct key *key)
{
        if (key->type == &key_type_keyring)
                return (void *)((unsigned long)key | KEYRING_PTR_SUBTYPE);
        return key;
}

static struct list_head keyring_name_hash[KEYRING_NAME_HASH_SIZE];
static DEFINE_RWLOCK(keyring_name_lock);

static inline unsigned keyring_hash(const char *desc)
{
        unsigned bucket = 0;

        for (; *desc; desc++)
                bucket += (unsigned char)*desc;

        return bucket & (KEYRING_NAME_HASH_SIZE - 1);
}

/*
 * The keyring key type definition.  Keyrings are simply keys of this type and
 * can be treated as ordinary keys in addition to having their own special
 * operations.
 */
static int keyring_preparse(struct key_preparsed_payload *prep);
static void keyring_free_preparse(struct key_preparsed_payload *prep);
static int keyring_instantiate(struct key *keyring,
                               struct key_preparsed_payload *prep);
static void keyring_revoke(struct key *keyring);
static void keyring_destroy(struct key *keyring);
static void keyring_describe(const struct key *keyring, struct seq_file *m);
static long keyring_read(const struct key *keyring,
                         char __user *buffer, size_t buflen);

struct key_type key_type_keyring = {
        .name           = "keyring",
        .def_datalen    = 0,
        .preparse       = keyring_preparse,
        .free_preparse  = keyring_free_preparse,
        .instantiate    = keyring_instantiate,
        .revoke         = keyring_revoke,
        .destroy        = keyring_destroy,
        .describe       = keyring_describe,
        .read           = keyring_read,
};
EXPORT_SYMBOL(key_type_keyring);

/*
 * Semaphore to serialise link/link calls to prevent two link calls in parallel
 * introducing a cycle.
 */
static DECLARE_RWSEM(keyring_serialise_link_sem);

/*
 * Publish the name of a keyring so that it can be found by name (if it has
 * one).
 */
static void keyring_publish_name(struct key *keyring)
{
        int bucket;

        if (keyring->description) {
                bucket = keyring_hash(keyring->description);

                write_lock(&keyring_name_lock);

                if (!keyring_name_hash[bucket].next)
                        INIT_LIST_HEAD(&keyring_name_hash[bucket]);

                list_add_tail(&keyring->name_link,
                              &keyring_name_hash[bucket]);

                write_unlock(&keyring_name_lock);
        }
}

/*
 * Preparse a keyring payload
 */
static int keyring_preparse(struct key_preparsed_payload *prep)
{
        return prep->datalen != 0 ? -EINVAL : 0;
}

/*
 * Free a preparse of a user defined key payload
 */
static void keyring_free_preparse(struct key_preparsed_payload *prep)
{
}

/*
 * Initialise a keyring.
 *
 * Returns 0 on success, -EINVAL if given any data.
 */
static int keyring_instantiate(struct key *keyring,
                               struct key_preparsed_payload *prep)
{
        assoc_array_init(&keyring->keys);
        /* make the keyring available by name if it has one */
        keyring_publish_name(keyring);
        return 0;
}

/*
 * Multiply 64-bits by 32-bits to 96-bits and fold back to 64-bit.  Ideally we'd
 * fold the carry back too, but that requires inline asm.
 */
static u64 mult_64x32_and_fold(u64 x, u32 y)
{
        u64 hi = (u64)(u32)(x >> 32) * y;
        u64 lo = (u64)(u32)(x) * y;
        return lo + ((u64)(u32)hi << 32) + (u32)(hi >> 32);
}

/*
 * Hash a key type and description.
 */
static unsigned long hash_key_type_and_desc(const struct keyring_index_key *index_key)
{
        const unsigned level_shift = ASSOC_ARRAY_LEVEL_STEP;
        const unsigned long fan_mask = ASSOC_ARRAY_FAN_MASK;
        const char *description = index_key->description;
        unsigned long hash, type;
        u32 piece;
        u64 acc;
        int n, desc_len = index_key->desc_len;

        type = (unsigned long)index_key->type;

        acc = mult_64x32_and_fold(type, desc_len + 13);
        acc = mult_64x32_and_fold(acc, 9207);
        for (;;) {
                n = desc_len;
                if (n <= 0)
                        break;
                if (n > 4)
                        n = 4;
                piece = 0;
                memcpy(&piece, description, n);
                description += n;
                desc_len -= n;
                acc = mult_64x32_and_fold(acc, piece);
                acc = mult_64x32_and_fold(acc, 9207);
        }

        /* Fold the hash down to 32 bits if need be. */
        hash = acc;
        if (ASSOC_ARRAY_KEY_CHUNK_SIZE == 32)
                hash ^= acc >> 32;

        /* Squidge all the keyrings into a separate part of the tree to
         * ordinary keys by making sure the lowest level segment in the hash is
         * zero for keyrings and non-zero otherwise.
         */
        if (index_key->type != &key_type_keyring && (hash & fan_mask) == 0)
                return hash | (hash >> (ASSOC_ARRAY_KEY_CHUNK_SIZE - level_shift)) | 1;
        if (index_key->type == &key_type_keyring && (hash & fan_mask) != 0)
                return (hash + (hash << level_shift)) & ~fan_mask;
        return hash;
}

/*
 * Build the next index key chunk.
 *
 * On 32-bit systems the index key is laid out as:
 *
 *      0       4       5       9...
 *      hash    desclen typeptr desc[]
 *
 * On 64-bit systems:
 *
 *      0       8       9       17...
 *      hash    desclen typeptr desc[]
 *
 * We return it one word-sized chunk at a time.
 */
static unsigned long keyring_get_key_chunk(const void *data, int level)
{
        const struct keyring_index_key *index_key = data;
        unsigned long chunk = 0;
        long offset = 0;
        int desc_len = index_key->desc_len, n = sizeof(chunk);

        level /= ASSOC_ARRAY_KEY_CHUNK_SIZE;
        switch (level) {
        case 0:
                return hash_key_type_and_desc(index_key);
        case 1:
                return ((unsigned long)index_key->type << 8) | desc_len;
        case 2:
                if (desc_len == 0)
                        return (u8)((unsigned long)index_key->type >>
                                    (ASSOC_ARRAY_KEY_CHUNK_SIZE - 8));
                n--;
                offset = 1;
        default:
                offset += sizeof(chunk) - 1;
                offset += (level - 3) * sizeof(chunk);
                if (offset >= desc_len)
                        return 0;
                desc_len -= offset;
                if (desc_len > n)
                        desc_len = n;
                offset += desc_len;
                do {
                        chunk <<= 8;
                        chunk |= ((u8*)index_key->description)[--offset];
                } while (--desc_len > 0);

                if (level == 2) {
                        chunk <<= 8;
                        chunk |= (u8)((unsigned long)index_key->type >>
                                      (ASSOC_ARRAY_KEY_CHUNK_SIZE - 8));
                }
                return chunk;
        }
}

static unsigned long keyring_get_object_key_chunk(const void *object, int level)
{
        const struct key *key = keyring_ptr_to_key(object);
        return keyring_get_key_chunk(&key->index_key, level);
}

static bool keyring_compare_object(const void *object, const void *data)
{
        const struct keyring_index_key *index_key = data;
        const struct key *key = keyring_ptr_to_key(object);

        return key->index_key.type == index_key->type &&
                key->index_key.desc_len == index_key->desc_len &&
                memcmp(key->index_key.description, index_key->description,
                       index_key->desc_len) == 0;
}

/*
 * Compare the index keys of a pair of objects and determine the bit position
 * at which they differ - if they differ.
 */
static int keyring_diff_objects(const void *object, const void *data)
{
        const struct key *key_a = keyring_ptr_to_key(object);
        const struct keyring_index_key *a = &key_a->index_key;
        const struct keyring_index_key *b = data;
        unsigned long seg_a, seg_b;
        int level, i;

        level = 0;
        seg_a = hash_key_type_and_desc(a);
        seg_b = hash_key_type_and_desc(b);
        if ((seg_a ^ seg_b) != 0)
                goto differ;

        /* The number of bits contributed by the hash is controlled by a
         * constant in the assoc_array headers.  Everything else thereafter we
         * can deal with as being machine word-size dependent.
         */
        level += ASSOC_ARRAY_KEY_CHUNK_SIZE / 8;
        seg_a = a->desc_len;
        seg_b = b->desc_len;
        if ((seg_a ^ seg_b) != 0)
                goto differ;

        /* The next bit may not work on big endian */
        level++;
        seg_a = (unsigned long)a->type;
        seg_b = (unsigned long)b->type;
        if ((seg_a ^ seg_b) != 0)
                goto differ;

        level += sizeof(unsigned long);
        if (a->desc_len == 0)
                goto same;

        i = 0;
        if (((unsigned long)a->description | (unsigned long)b->description) &
            (sizeof(unsigned long) - 1)) {
                do {
                        seg_a = *(unsigned long *)(a->description + i);
                        seg_b = *(unsigned long *)(b->description + i);
                        if ((seg_a ^ seg_b) != 0)
                                goto differ_plus_i;
                        i += sizeof(unsigned long);
                } while (i < (a->desc_len & (sizeof(unsigned long) - 1)));
        }

        for (; i < a->desc_len; i++) {
                seg_a = *(unsigned char *)(a->description + i);
                seg_b = *(unsigned char *)(b->description + i);
                if ((seg_a ^ seg_b) != 0)
                        goto differ_plus_i;
        }

same:
        return -1;

differ_plus_i:
        level += i;
differ:
        i = level * 8 + __ffs(seg_a ^ seg_b);
        return i;
}

/*
 * Free an object after stripping the keyring flag off of the pointer.
 */
static void keyring_free_object(void *object)
{
        key_put(keyring_ptr_to_key(object));
}

/*
 * Operations for keyring management by the index-tree routines.
 */
static const struct assoc_array_ops keyring_assoc_array_ops = {
        .get_key_chunk          = keyring_get_key_chunk,
        .get_object_key_chunk   = keyring_get_object_key_chunk,
        .compare_object         = keyring_compare_object,
        .diff_objects           = keyring_diff_objects,
        .free_object            = keyring_free_object,
};

/*
 * Clean up a keyring when it is destroyed.  Unpublish its name if it had one
 * and dispose of its data.
 *
 * The garbage collector detects the final key_put(), removes the keyring from
 * the serial number tree and then does RCU synchronisation before coming here,
 * so we shouldn't need to worry about code poking around here with the RCU
 * readlock held by this time.
 */
static void keyring_destroy(struct key *keyring)
{
        if (keyring->description) {
                write_lock(&keyring_name_lock);

                if (keyring->name_link.next != NULL &&
                    !list_empty(&keyring->name_link))
                        list_del(&keyring->name_link);

                write_unlock(&keyring_name_lock);
        }

        if (keyring->restrict_link) {
                struct key_restriction *keyres = keyring->restrict_link;

                key_put(keyres->key);
                kfree(keyres);
        }

        assoc_array_destroy(&keyring->keys, &keyring_assoc_array_ops);
}

/*
 * Describe a keyring for /proc.
 */
static void keyring_describe(const struct key *keyring, struct seq_file *m)
{
        if (keyring->description)
                seq_puts(m, keyring->description);
        else
                seq_puts(m, "[anon]");

        if (key_is_positive(keyring)) {
                if (keyring->keys.nr_leaves_on_tree != 0)
                        seq_printf(m, ": %lu", keyring->keys.nr_leaves_on_tree);
                else
                        seq_puts(m, ": empty");
        }
}

struct keyring_read_iterator_context {
        size_t                  buflen;
        size_t                  count;
        key_serial_t __user     *buffer;
};

static int keyring_read_iterator(const void *object, void *data)
{
        struct keyring_read_iterator_context *ctx = data;
        const struct key *key = keyring_ptr_to_key(object);
        int ret;

        kenter("{%s,%d},,{%zu/%zu}",
               key->type->name, key->serial, ctx->count, ctx->buflen);

        if (ctx->count >= ctx->buflen)
                return 1;

        ret = put_user(key->serial, ctx->buffer);
        if (ret < 0)
                return ret;
        ctx->buffer++;
        ctx->count += sizeof(key->serial);
        return 0;
}

/*
 * Read a list of key IDs from the keyring's contents in binary form
 *
 * The keyring's semaphore is read-locked by the caller.  This prevents someone
 * from modifying it under us - which could cause us to read key IDs multiple
 * times.
 */
static long keyring_read(const struct key *keyring,
                         char __user *buffer, size_t buflen)
{
        struct keyring_read_iterator_context ctx;
        long ret;

        kenter("{%d},,%zu", key_serial(keyring), buflen);

        if (buflen & (sizeof(key_serial_t) - 1))
                return -EINVAL;

        /* Copy as many key IDs as fit into the buffer */
        if (buffer && buflen) {
                ctx.buffer = (key_serial_t __user *)buffer;
                ctx.buflen = buflen;
                ctx.count = 0;
                ret = assoc_array_iterate(&keyring->keys,
                                          keyring_read_iterator, &ctx);
                if (ret < 0) {
                        kleave(" = %ld [iterate]", ret);
                        return ret;
                }
        }

        /* Return the size of the buffer needed */
        ret = keyring->keys.nr_leaves_on_tree * sizeof(key_serial_t);
        if (ret <= buflen)
                kleave("= %ld [ok]", ret);
        else
                kleave("= %ld [buffer too small]", ret);
        return ret;
}

/*
 * Allocate a keyring and link into the destination keyring.
 */
struct key *keyring_alloc(const char *description, kuid_t uid, kgid_t gid,
                          const struct cred *cred, key_perm_t perm,
                          unsigned long flags,
                          struct key_restriction *restrict_link,
                          struct key *dest)
{
        struct key *keyring;
        int ret;

        keyring = key_alloc(&key_type_keyring, description,
                            uid, gid, cred, perm, flags, restrict_link);
        if (!IS_ERR(keyring)) {
                ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
                if (ret < 0) {
                        key_put(keyring);
                        keyring = ERR_PTR(ret);
                }
        }

        return keyring;
}
EXPORT_SYMBOL(keyring_alloc);

/**
 * restrict_link_reject - Give -EPERM to restrict link
 * @keyring: The keyring being added to.
 * @type: The type of key being added.
 * @payload: The payload of the key intended to be added.
 * @data: Additional data for evaluating restriction.
 *
 * Reject the addition of any links to a keyring.  It can be overridden by
 * passing KEY_ALLOC_BYPASS_RESTRICTION to key_instantiate_and_link() when
 * adding a key to a keyring.
 *
 * This is meant to be stored in a key_restriction structure which is passed
 * in the restrict_link parameter to keyring_alloc().
 */
int restrict_link_reject(struct key *keyring,
                         const struct key_type *type,
                         const union key_payload *payload,
                         struct key *restriction_key)
{
        return -EPERM;
}

/*
 * By default, we keys found by getting an exact match on their descriptions.
 */
bool key_default_cmp(const struct key *key,
                     const struct key_match_data *match_data)
{
        return strcmp(key->description, match_data->raw_data) == 0;
}

/*
 * Iteration function to consider each key found.
 */
static int keyring_search_iterator(const void *object, void *iterator_data)
{
        struct keyring_search_context *ctx = iterator_data;
        const struct key *key = keyring_ptr_to_key(object);
        unsigned long kflags = READ_ONCE(key->flags);
        short state = READ_ONCE(key->state);

        kenter("{%d}", key->serial);

        /* ignore keys not of this type */
        if (key->type != ctx->index_key.type) {
                kleave(" = 0 [!type]");
                return 0;
        }

        /* skip invalidated, revoked and expired keys */
        if (ctx->flags & KEYRING_SEARCH_DO_STATE_CHECK) {
                time_t expiry = READ_ONCE(key->expiry);

                if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
                              (1 << KEY_FLAG_REVOKED))) {
                        ctx->result = ERR_PTR(-EKEYREVOKED);
                        kleave(" = %d [invrev]", ctx->skipped_ret);
                        goto skipped;
                }

                if (expiry && ctx->now.tv_sec >= expiry) {
                        if (!(ctx->flags & KEYRING_SEARCH_SKIP_EXPIRED))
                                ctx->result = ERR_PTR(-EKEYEXPIRED);
                        kleave(" = %d [expire]", ctx->skipped_ret);
                        goto skipped;
                }
        }

        /* keys that don't match */
        if (!ctx->match_data.cmp(key, &ctx->match_data)) {
                kleave(" = 0 [!match]");
                return 0;
        }

        /* key must have search permissions */
        if (!(ctx->flags & KEYRING_SEARCH_NO_CHECK_PERM) &&
            key_task_permission(make_key_ref(key, ctx->possessed),
                                ctx->cred, KEY_NEED_SEARCH) < 0) {
                ctx->result = ERR_PTR(-EACCES);
                kleave(" = %d [!perm]", ctx->skipped_ret);
                goto skipped;
        }

        if (ctx->flags & KEYRING_SEARCH_DO_STATE_CHECK) {
                /* we set a different error code if we pass a negative key */
                if (state < 0) {
                        ctx->result = ERR_PTR(state);
                        kleave(" = %d [neg]", ctx->skipped_ret);
                        goto skipped;
                }
        }

        /* Found */
        ctx->result = make_key_ref(key, ctx->possessed);
        kleave(" = 1 [found]");
        return 1;

skipped:
        return ctx->skipped_ret;
}

/*
 * Search inside a keyring for a key.  We can search by walking to it
 * directly based on its index-key or we can iterate over the entire
 * tree looking for it, based on the match function.
 */
static int search_keyring(struct key *keyring, struct keyring_search_context *ctx)
{
        if (ctx->match_data.lookup_type == KEYRING_SEARCH_LOOKUP_DIRECT) {
                const void *object;

                object = assoc_array_find(&keyring->keys,
                                          &keyring_assoc_array_ops,
                                          &ctx->index_key);
                return object ? ctx->iterator(object, ctx) : 0;
        }
        return assoc_array_iterate(&keyring->keys, ctx->iterator, ctx);
}

/*
 * Search a tree of keyrings that point to other keyrings up to the maximum
 * depth.
 */
static bool search_nested_keyrings(struct key *keyring,
                                   struct keyring_search_context *ctx)
{
        struct {
                struct key *keyring;
                struct assoc_array_node *node;
                int slot;
        } stack[KEYRING_SEARCH_MAX_DEPTH];

        struct assoc_array_shortcut *shortcut;
        struct assoc_array_node *node;
        struct assoc_array_ptr *ptr;
        struct key *key;
        int sp = 0, slot;

        kenter("{%d},{%s,%s}",
               keyring->serial,
               ctx->index_key.type->name,
               ctx->index_key.description);

#define STATE_CHECKS (KEYRING_SEARCH_NO_STATE_CHECK | KEYRING_SEARCH_DO_STATE_CHECK)
        BUG_ON((ctx->flags & STATE_CHECKS) == 0 ||
               (ctx->flags & STATE_CHECKS) == STATE_CHECKS);

        if (ctx->index_key.description)
                ctx->index_key.desc_len = strlen(ctx->index_key.description);

        /* Check to see if this top-level keyring is what we are looking for
         * and whether it is valid or not.
         */
        if (ctx->match_data.lookup_type == KEYRING_SEARCH_LOOKUP_ITERATE ||
            keyring_compare_object(keyring, &ctx->index_key)) {
                ctx->skipped_ret = 2;
                switch (ctx->iterator(keyring_key_to_ptr(keyring), ctx)) {
                case 1:
                        goto found;
                case 2:
                        return false;
                default:
                        break;
                }
        }

        ctx->skipped_ret = 0;

        /* Start processing a new keyring */
descend_to_keyring:
        kdebug("descend to %d", keyring->serial);
        if (keyring->flags & ((1 << KEY_FLAG_INVALIDATED) |
                              (1 << KEY_FLAG_REVOKED)))
                goto not_this_keyring;

        /* Search through the keys in this keyring before its searching its
         * subtrees.
         */
        if (search_keyring(keyring, ctx))
                goto found;

        /* Then manually iterate through the keyrings nested in this one.
         *
         * Start from the root node of the index tree.  Because of the way the
         * hash function has been set up, keyrings cluster on the leftmost
         * branch of the root node (root slot 0) or in the root node itself.
         * Non-keyrings avoid the leftmost branch of the root entirely (root
         * slots 1-15).
         */
        ptr = READ_ONCE(keyring->keys.root);
        if (!ptr)
                goto not_this_keyring;

        if (assoc_array_ptr_is_shortcut(ptr)) {
                /* If the root is a shortcut, either the keyring only contains
                 * keyring pointers (everything clusters behind root slot 0) or
                 * doesn't contain any keyring pointers.
                 */
                shortcut = assoc_array_ptr_to_shortcut(ptr);
                smp_read_barrier_depends();
                if ((shortcut->index_key[0] & ASSOC_ARRAY_FAN_MASK) != 0)
                        goto not_this_keyring;

                ptr = READ_ONCE(shortcut->next_node);
                node = assoc_array_ptr_to_node(ptr);
                goto begin_node;
        }

        node = assoc_array_ptr_to_node(ptr);
        smp_read_barrier_depends();

        ptr = node->slots[0];
        if (!assoc_array_ptr_is_meta(ptr))
                goto begin_node;

descend_to_node:
        /* Descend to a more distal node in this keyring's content tree and go
         * through that.
         */
        kdebug("descend");
        if (assoc_array_ptr_is_shortcut(ptr)) {
                shortcut = assoc_array_ptr_to_shortcut(ptr);
                smp_read_barrier_depends();
                ptr = READ_ONCE(shortcut->next_node);
                BUG_ON(!assoc_array_ptr_is_node(ptr));
        }
        node = assoc_array_ptr_to_node(ptr);

begin_node:
        kdebug("begin_node");
        smp_read_barrier_depends();
        slot = 0;
ascend_to_node:
        /* Go through the slots in a node */
        for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
                ptr = READ_ONCE(node->slots[slot]);

                if (assoc_array_ptr_is_meta(ptr) && node->back_pointer)
                        goto descend_to_node;

                if (!keyring_ptr_is_keyring(ptr))
                        continue;

                key = keyring_ptr_to_key(ptr);

                if (sp >= KEYRING_SEARCH_MAX_DEPTH) {
                        if (ctx->flags & KEYRING_SEARCH_DETECT_TOO_DEEP) {
                                ctx->result = ERR_PTR(-ELOOP);
                                return false;
                        }
                        goto not_this_keyring;
                }

                /* Search a nested keyring */
                if (!(ctx->flags & KEYRING_SEARCH_NO_CHECK_PERM) &&
                    key_task_permission(make_key_ref(key, ctx->possessed),
                                        ctx->cred, KEY_NEED_SEARCH) < 0)
                        continue;

                /* stack the current position */
                stack[sp].keyring = keyring;
                stack[sp].node = node;
                stack[sp].slot = slot;
                sp++;

                /* begin again with the new keyring */
                keyring = key;
                goto descend_to_keyring;
        }

        /* We've dealt with all the slots in the current node, so now we need
         * to ascend to the parent and continue processing there.
         */
        ptr = READ_ONCE(node->back_pointer);
        slot = node->parent_slot;

        if (ptr && assoc_array_ptr_is_shortcut(ptr)) {
                shortcut = assoc_array_ptr_to_shortcut(ptr);
                smp_read_barrier_depends();
                ptr = READ_ONCE(shortcut->back_pointer);
                slot = shortcut->parent_slot;
        }
        if (!ptr)
                goto not_this_keyring;
        node = assoc_array_ptr_to_node(ptr);
        smp_read_barrier_depends();
        slot++;

        /* If we've ascended to the root (zero backpointer), we must have just
         * finished processing the leftmost branch rather than the root slots -
         * so there can't be any more keyrings for us to find.
         */
        if (node->back_pointer) {
                kdebug("ascend %d", slot);
                goto ascend_to_node;
        }

        /* The keyring we're looking at was disqualified or didn't contain a
         * matching key.
         */
not_this_keyring:
        kdebug("not_this_keyring %d", sp);
        if (sp <= 0) {
                kleave(" = false");
                return false;
        }

        /* Resume the processing of a keyring higher up in the tree */
        sp--;
        keyring = stack[sp].keyring;
        node = stack[sp].node;
        slot = stack[sp].slot + 1;
        kdebug("ascend to %d [%d]", keyring->serial, slot);
        goto ascend_to_node;

        /* We found a viable match */
found:
        key = key_ref_to_ptr(ctx->result);
        key_check(key);
        if (!(ctx->flags & KEYRING_SEARCH_NO_UPDATE_TIME)) {
                key->last_used_at = ctx->now.tv_sec;
                keyring->last_used_at = ctx->now.tv_sec;
                while (sp > 0)
                        stack[--sp].keyring->last_used_at = ctx->now.tv_sec;
        }
        kleave(" = true");
        return true;
}

/**
 * keyring_search_aux - Search a keyring tree for a key matching some criteria
 * @keyring_ref: A pointer to the keyring with possession indicator.
 * @ctx: The keyring search context.
 *
 * Search the supplied keyring tree for a key that matches the criteria given.
 * The root keyring and any linked keyrings must grant Search permission to the
 * caller to be searchable and keys can only be found if they too grant Search
 * to the caller. The possession flag on the root keyring pointer controls use
 * of the possessor bits in permissions checking of the entire tree.  In
 * addition, the LSM gets to forbid keyring searches and key matches.
 *
 * The search is performed as a breadth-then-depth search up to the prescribed
 * limit (KEYRING_SEARCH_MAX_DEPTH).
 *
 * Keys are matched to the type provided and are then filtered by the match
 * function, which is given the description to use in any way it sees fit.  The
 * match function may use any attributes of a key that it wishes to to
 * determine the match.  Normally the match function from the key type would be
 * used.
 *
 * RCU can be used to prevent the keyring key lists from disappearing without
 * the need to take lots of locks.
 *
 * Returns a pointer to the found key and increments the key usage count if
 * successful; -EAGAIN if no matching keys were found, or if expired or revoked
 * keys were found; -ENOKEY if only negative keys were found; -ENOTDIR if the
 * specified keyring wasn't a keyring.
 *
 * In the case of a successful return, the possession attribute from
 * @keyring_ref is propagated to the returned key reference.
 */
key_ref_t keyring_search_aux(key_ref_t keyring_ref,
                             struct keyring_search_context *ctx)
{
        struct key *keyring;
        long err;

        ctx->iterator = keyring_search_iterator;
        ctx->possessed = is_key_possessed(keyring_ref);
        ctx->result = ERR_PTR(-EAGAIN);

        keyring = key_ref_to_ptr(keyring_ref);
        key_check(keyring);

        if (keyring->type != &key_type_keyring)
                return ERR_PTR(-ENOTDIR);

        if (!(ctx->flags & KEYRING_SEARCH_NO_CHECK_PERM)) {
                err = key_task_permission(keyring_ref, ctx->cred, KEY_NEED_SEARCH);
                if (err < 0)
                        return ERR_PTR(err);
        }

        rcu_read_lock();
        ctx->now = current_kernel_time();
        if (search_nested_keyrings(keyring, ctx))
                __key_get(key_ref_to_ptr(ctx->result));
        rcu_read_unlock();
        return ctx->result;
}

/**
 * keyring_search - Search the supplied keyring tree for a matching key
 * @keyring: The root of the keyring tree to be searched.
 * @type: The type of keyring we want to find.
 * @description: The name of the keyring we want to find.
 *
 * As keyring_search_aux() above, but using the current task's credentials and
 * type's default matching function and preferred search method.
 */
key_ref_t keyring_search(key_ref_t keyring,
                         struct key_type *type,
                         const char *description)
{
        struct keyring_search_context ctx = {
                .index_key.type         = type,
                .index_key.description  = description,
                .cred                   = current_cred(),
                .match_data.cmp         = key_default_cmp,
                .match_data.raw_data    = description,
                .match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
                .flags                  = KEYRING_SEARCH_DO_STATE_CHECK,
        };
        key_ref_t key;
        int ret;

        if (type->match_preparse) {
                ret = type->match_preparse(&ctx.match_data);
                if (ret < 0)
                        return ERR_PTR(ret);
        }

        key = keyring_search_aux(keyring, &ctx);

        if (type->match_free)
                type->match_free(&ctx.match_data);
        return key;
}
EXPORT_SYMBOL(keyring_search);

static struct key_restriction *keyring_restriction_alloc(
        key_restrict_link_func_t check)
{
        struct key_restriction *keyres =
                kzalloc(sizeof(struct key_restriction), GFP_KERNEL);

        if (!keyres)
                return ERR_PTR(-ENOMEM);

        keyres->check = check;

        return keyres;
}

/*
 * Semaphore to serialise restriction setup to prevent reference count
 * cycles through restriction key pointers.
 */
static DECLARE_RWSEM(keyring_serialise_restrict_sem);

/*
 * Check for restriction cycles that would prevent keyring garbage collection.
 * keyring_serialise_restrict_sem must be held.
 */
static bool keyring_detect_restriction_cycle(const struct key *dest_keyring,
                                             struct key_restriction *keyres)
{
        while (keyres && keyres->key &&
               keyres->key->type == &key_type_keyring) {
                if (keyres->key == dest_keyring)
                        return true;

                keyres = keyres->key->restrict_link;
        }

        return false;
}

/**
 * keyring_restrict - Look up and apply a restriction to a keyring
 *
 * @keyring: The keyring to be restricted
 * @restriction: The restriction options to apply to the keyring
 */
int keyring_restrict(key_ref_t keyring_ref, const char *type,
                     const char *restriction)
{
        struct key *keyring;
        struct key_type *restrict_type = NULL;
        struct key_restriction *restrict_link;
        int ret = 0;

        keyring = key_ref_to_ptr(keyring_ref);
        key_check(keyring);

        if (keyring->type != &key_type_keyring)
                return -ENOTDIR;

        if (!type) {
                restrict_link = keyring_restriction_alloc(restrict_link_reject);
        } else {
                restrict_type = key_type_lookup(type);

                if (IS_ERR(restrict_type))
                        return PTR_ERR(restrict_type);

                if (!restrict_type->lookup_restriction) {
                        ret = -ENOENT;
                        goto error;
                }

                restrict_link = restrict_type->lookup_restriction(restriction);
        }

        if (IS_ERR(restrict_link)) {
                ret = PTR_ERR(restrict_link);
                goto error;
        }

        down_write(&keyring->sem);
        down_write(&keyring_serialise_restrict_sem);

        if (keyring->restrict_link)
                ret = -EEXIST;
        else if (keyring_detect_restriction_cycle(keyring, restrict_link))
                ret = -EDEADLK;
        else
                keyring->restrict_link = restrict_link;

        up_write(&keyring_serialise_restrict_sem);
        up_write(&keyring->sem);

        if (ret < 0) {
                key_put(restrict_link->key);
                kfree(restrict_link);
        }

error:
        if (restrict_type)
                key_type_put(restrict_type);

        return ret;
}
EXPORT_SYMBOL(keyring_restrict);

/*
 * Search the given keyring for a key that might be updated.
 *
 * The caller must guarantee that the keyring is a keyring and that the
 * permission is granted to modify the keyring as no check is made here.  The
 * caller must also hold a lock on the keyring semaphore.
 *
 * Returns a pointer to the found key with usage count incremented if
 * successful and returns NULL if not found.  Revoked and invalidated keys are
 * skipped over.
 *
 * If successful, the possession indicator is propagated from the keyring ref
 * to the returned key reference.
 */
key_ref_t find_key_to_update(key_ref_t keyring_ref,
                             const struct keyring_index_key *index_key)
{
        struct key *keyring, *key;
        const void *object;

        keyring = key_ref_to_ptr(keyring_ref);

        kenter("{%d},{%s,%s}",
               keyring->serial, index_key->type->name, index_key->description);

        object = assoc_array_find(&keyring->keys, &keyring_assoc_array_ops,
                                  index_key);

        if (object)
                goto found;

        kleave(" = NULL");
        return NULL;

found:
        key = keyring_ptr_to_key(object);
        if (key->flags & ((1 << KEY_FLAG_INVALIDATED) |
                          (1 << KEY_FLAG_REVOKED))) {
                kleave(" = NULL [x]");
                return NULL;
        }
        __key_get(key);
        kleave(" = {%d}", key->serial);
        return make_key_ref(key, is_key_possessed(keyring_ref));
}

/*
 * Find a keyring with the specified name.
 *
 * Only keyrings that have nonzero refcount, are not revoked, and are owned by a
 * user in the current user namespace are considered.  If @uid_keyring is %true,
 * the keyring additionally must have been allocated as a user or user session
 * keyring; otherwise, it must grant Search permission directly to the caller.
 *
 * Returns a pointer to the keyring with the keyring's refcount having being
 * incremented on success.  -ENOKEY is returned if a key could not be found.
 */
struct key *find_keyring_by_name(const char *name, bool uid_keyring)
{
        struct key *keyring;
        int bucket;

        if (!name)
                return ERR_PTR(-EINVAL);

        bucket = keyring_hash(name);

        read_lock(&keyring_name_lock);

        if (keyring_name_hash[bucket].next) {
                /* search this hash bucket for a keyring with a matching name
                 * that's readable and that hasn't been revoked */
                list_for_each_entry(keyring,
                                    &keyring_name_hash[bucket],
                                    name_link
                                    ) {
                        if (!kuid_has_mapping(current_user_ns(), keyring->user->uid))
                                continue;

                        if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
                                continue;

                        if (strcmp(keyring->description, name) != 0)
                                continue;

                        if (uid_keyring) {
                                if (!test_bit(KEY_FLAG_UID_KEYRING,
                                              &keyring->flags))
                                        continue;
                        } else {
                                if (key_permission(make_key_ref(keyring, 0),
                                                   KEY_NEED_SEARCH) < 0)
                                        continue;
                        }

                        /* we've got a match but we might end up racing with
                         * key_cleanup() if the keyring is currently 'dead'
                         * (ie. it has a zero usage count) */
                        if (!refcount_inc_not_zero(&keyring->usage))
                                continue;
                        keyring->last_used_at = current_kernel_time().tv_sec;
                        goto out;
                }
        }

        keyring = ERR_PTR(-ENOKEY);
out:
        read_unlock(&keyring_name_lock);
        return keyring;
}

static int keyring_detect_cycle_iterator(const void *object,
                                         void *iterator_data)
{
        struct keyring_search_context *ctx = iterator_data;
        const struct key *key = keyring_ptr_to_key(object);

        kenter("{%d}", key->serial);

        /* We might get a keyring with matching index-key that is nonetheless a
         * different keyring. */
        if (key != ctx->match_data.raw_data)
                return 0;

        ctx->result = ERR_PTR(-EDEADLK);
        return 1;
}

/*
 * See if a cycle will will be created by inserting acyclic tree B in acyclic
 * tree A at the topmost level (ie: as a direct child of A).
 *
 * Since we are adding B to A at the top level, checking for cycles should just
 * be a matter of seeing if node A is somewhere in tree B.
 */
static int keyring_detect_cycle(struct key *A, struct key *B)
{
        struct keyring_search_context ctx = {
                .index_key              = A->index_key,
                .match_data.raw_data    = A,
                .match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
                .iterator               = keyring_detect_cycle_iterator,
                .flags                  = (KEYRING_SEARCH_NO_STATE_CHECK |
                                           KEYRING_SEARCH_NO_UPDATE_TIME |
                                           KEYRING_SEARCH_NO_CHECK_PERM |
                                           KEYRING_SEARCH_DETECT_TOO_DEEP),
        };

        rcu_read_lock();
        search_nested_keyrings(B, &ctx);
        rcu_read_unlock();
        return PTR_ERR(ctx.result) == -EAGAIN ? 0 : PTR_ERR(ctx.result);
}

/*
 * Preallocate memory so that a key can be linked into to a keyring.
 */
int __key_link_begin(struct key *keyring,
                     const struct keyring_index_key *index_key,
                     struct assoc_array_edit **_edit)
        __acquires(&keyring->sem)
        __acquires(&keyring_serialise_link_sem)
{
        struct assoc_array_edit *edit;
        int ret;

        kenter("%d,%s,%s,",
               keyring->serial, index_key->type->name, index_key->description);

        BUG_ON(index_key->desc_len == 0);

        if (keyring->type != &key_type_keyring)
                return -ENOTDIR;

        down_write(&keyring->sem);

        ret = -EKEYREVOKED;
        if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
                goto error_krsem;

        /* serialise link/link calls to prevent parallel calls causing a cycle
         * when linking two keyring in opposite orders */
        if (index_key->type == &key_type_keyring)
                down_write(&keyring_serialise_link_sem);

        /* Create an edit script that will insert/replace the key in the
         * keyring tree.
         */
        edit = assoc_array_insert(&keyring->keys,
                                  &keyring_assoc_array_ops,
                                  index_key,
                                  NULL);
        if (IS_ERR(edit)) {
                ret = PTR_ERR(edit);
                goto error_sem;
        }

        /* If we're not replacing a link in-place then we're going to need some
         * extra quota.
         */
        if (!edit->dead_leaf) {
                ret = key_payload_reserve(keyring,
                                          keyring->datalen + KEYQUOTA_LINK_BYTES);
                if (ret < 0)
                        goto error_cancel;
        }

        *_edit = edit;
        kleave(" = 0");
        return 0;

error_cancel:
        assoc_array_cancel_edit(edit);
error_sem:
        if (index_key->type == &key_type_keyring)
                up_write(&keyring_serialise_link_sem);
error_krsem:
        up_write(&keyring->sem);
        kleave(" = %d", ret);
        return ret;
}

/*
 * Check already instantiated keys aren't going to be a problem.
 *
 * The caller must have called __key_link_begin(). Don't need to call this for
 * keys that were created since __key_link_begin() was called.
 */
int __key_link_check_live_key(struct key *keyring, struct key *key)
{
        if (key->type == &key_type_keyring)
                /* check that we aren't going to create a cycle by linking one
                 * keyring to another */
                return keyring_detect_cycle(keyring, key);
        return 0;
}

/*
 * Link a key into to a keyring.
 *
 * Must be called with __key_link_begin() having being called.  Discards any
 * already extant link to matching key if there is one, so that each keyring
 * holds at most one link to any given key of a particular type+description
 * combination.
 */
void __key_link(struct key *key, struct assoc_array_edit **_edit)
{
        __key_get(key);
        assoc_array_insert_set_object(*_edit, keyring_key_to_ptr(key));
        assoc_array_apply_edit(*_edit);
        *_edit = NULL;
}

/*
 * Finish linking a key into to a keyring.
 *
 * Must be called with __key_link_begin() having being called.
 */
void __key_link_end(struct key *keyring,
                    const struct keyring_index_key *index_key,
                    struct assoc_array_edit *edit)
        __releases(&keyring->sem)
        __releases(&keyring_serialise_link_sem)
{
        BUG_ON(index_key->type == NULL);
        kenter("%d,%s,", keyring->serial, index_key->type->name);

        if (index_key->type == &key_type_keyring)
                up_write(&keyring_serialise_link_sem);

        if (edit) {
                if (!edit->dead_leaf) {
                        key_payload_reserve(keyring,
                                keyring->datalen - KEYQUOTA_LINK_BYTES);
                }
                assoc_array_cancel_edit(edit);
        }
        up_write(&keyring->sem);
}

/*
 * Check addition of keys to restricted keyrings.
 */
static int __key_link_check_restriction(struct key *keyring, struct key *key)
{
        if (!keyring->restrict_link || !keyring->restrict_link->check)
                return 0;
        return keyring->restrict_link->check(keyring, key->type, &key->payload,
                                             keyring->restrict_link->key);
}

/**
 * key_link - Link a key to a keyring
 * @keyring: The keyring to make the link in.
 * @key: The key to link to.
 *
 * Make a link in a keyring to a key, such that the keyring holds a reference
 * on that key and the key can potentially be found by searching that keyring.
 *
 * This function will write-lock the keyring's semaphore and will consume some
 * of the user's key data quota to hold the link.
 *
 * Returns 0 if successful, -ENOTDIR if the keyring isn't a keyring,
 * -EKEYREVOKED if the keyring has been revoked, -ENFILE if the keyring is
 * full, -EDQUOT if there is insufficient key data quota remaining to add
 * another link or -ENOMEM if there's insufficient memory.
 *
 * It is assumed that the caller has checked that it is permitted for a link to
 * be made (the keyring should have Write permission and the key Link
 * permission).
 */
int key_link(struct key *keyring, struct key *key)
{
        struct assoc_array_edit *edit;
        int ret;

        kenter("{%d,%d}", keyring->serial, refcount_read(&keyring->usage));

        key_check(keyring);
        key_check(key);

        ret = __key_link_begin(keyring, &key->index_key, &edit);
        if (ret == 0) {
                kdebug("begun {%d,%d}", keyring->serial, refcount_read(&keyring->usage));
                ret = __key_link_check_restriction(keyring, key);
                if (ret == 0)
                        ret = __key_link_check_live_key(keyring, key);
                if (ret == 0)
                        __key_link(key, &edit);
                __key_link_end(keyring, &key->index_key, edit);
        }

        kleave(" = %d {%d,%d}", ret, keyring->serial, refcount_read(&keyring->usage));
        return ret;
}
EXPORT_SYMBOL(key_link);

/**
 * key_unlink - Unlink the first link to a key from a keyring.
 * @keyring: The keyring to remove the link from.
 * @key: The key the link is to.
 *
 * Remove a link from a keyring to a key.
 *
 * This function will write-lock the keyring's semaphore.
 *
 * Returns 0 if successful, -ENOTDIR if the keyring isn't a keyring, -ENOENT if
 * the key isn't linked to by the keyring or -ENOMEM if there's insufficient
 * memory.
 *
 * It is assumed that the caller has checked that it is permitted for a link to
 * be removed (the keyring should have Write permission; no permissions are
 * required on the key).
 */
int key_unlink(struct key *keyring, struct key *key)
{
        struct assoc_array_edit *edit;
        int ret;

        key_check(keyring);
        key_check(key);

        if (keyring->type != &key_type_keyring)
                return -ENOTDIR;

        down_write(&keyring->sem);

        edit = assoc_array_delete(&keyring->keys, &keyring_assoc_array_ops,
                                  &key->index_key);
        if (IS_ERR(edit)) {
                ret = PTR_ERR(edit);
                goto error;
        }
        ret = -ENOENT;
        if (edit == NULL)
                goto error;

        assoc_array_apply_edit(edit);
        key_payload_reserve(keyring, keyring->datalen - KEYQUOTA_LINK_BYTES);
        ret = 0;

error:
        up_write(&keyring->sem);
        return ret;
}
EXPORT_SYMBOL(key_unlink);

/**
 * keyring_clear - Clear a keyring
 * @keyring: The keyring to clear.
 *
 * Clear the contents of the specified keyring.
 *
 * Returns 0 if successful or -ENOTDIR if the keyring isn't a keyring.
 */
int keyring_clear(struct key *keyring)
{
        struct assoc_array_edit *edit;
        int ret;

        if (keyring->type != &key_type_keyring)
                return -ENOTDIR;

        down_write(&keyring->sem);

        edit = assoc_array_clear(&keyring->keys, &keyring_assoc_array_ops);
        if (IS_ERR(edit)) {
                ret = PTR_ERR(edit);
        } else {
                if (edit)
                        assoc_array_apply_edit(edit);
                key_payload_reserve(keyring, 0);
                ret = 0;
        }

        up_write(&keyring->sem);
        return ret;
}
EXPORT_SYMBOL(keyring_clear);

/*
 * Dispose of the links from a revoked keyring.
 *
 * This is called with the key sem write-locked.
 */
static void keyring_revoke(struct key *keyring)
{
        struct assoc_array_edit *edit;

        edit = assoc_array_clear(&keyring->keys, &keyring_assoc_array_ops);
        if (!IS_ERR(edit)) {
                if (edit)
                        assoc_array_apply_edit(edit);
                key_payload_reserve(keyring, 0);
        }
}

static bool keyring_gc_select_iterator(void *object, void *iterator_data)
{
        struct key *key = keyring_ptr_to_key(object);
        time_t *limit = iterator_data;

        if (key_is_dead(key, *limit))
                return false;
        key_get(key);
        return true;
}

static int keyring_gc_check_iterator(const void *object, void *iterator_data)
{
        const struct key *key = keyring_ptr_to_key(object);
        time_t *limit = iterator_data;

        key_check(key);
        return key_is_dead(key, *limit);
}

/*
 * Garbage collect pointers from a keyring.
 *
 * Not called with any locks held.  The keyring's key struct will not be
 * deallocated under us as only our caller may deallocate it.
 */
void keyring_gc(struct key *keyring, time_t limit)
{
        int result;

        kenter("%x{%s}", keyring->serial, keyring->description ?: "");

        if (keyring->flags & ((1 << KEY_FLAG_INVALIDATED) |
                              (1 << KEY_FLAG_REVOKED)))
                goto dont_gc;

        /* scan the keyring looking for dead keys */
        rcu_read_lock();
        result = assoc_array_iterate(&keyring->keys,
                                     keyring_gc_check_iterator, &limit);
        rcu_read_unlock();
        if (result == true)
                goto do_gc;

dont_gc:
        kleave(" [no gc]");
        return;

do_gc:
        down_write(&keyring->sem);
        assoc_array_gc(&keyring->keys, &keyring_assoc_array_ops,
                       keyring_gc_select_iterator, &limit);
        up_write(&keyring->sem);
        kleave(" [gc]");
}

/*
 * Garbage collect restriction pointers from a keyring.
 *
 * Keyring restrictions are associated with a key type, and must be cleaned
 * up if the key type is unregistered. The restriction is altered to always
 * reject additional keys so a keyring cannot be opened up by unregistering
 * a key type.
 *
 * Not called with any keyring locks held. The keyring's key struct will not
 * be deallocated under us as only our caller may deallocate it.
 *
 * The caller is required to hold key_types_sem and dead_type->sem. This is
 * fulfilled by key_gc_keytype() holding the locks on behalf of
 * key_garbage_collector(), which it invokes on a workqueue.
 */
void keyring_restriction_gc(struct key *keyring, struct key_type *dead_type)
{
        struct key_restriction *keyres;

        kenter("%x{%s}", keyring->serial, keyring->description ?: "");

        /*
         * keyring->restrict_link is only assigned at key allocation time
         * or with the key type locked, so the only values that could be
         * concurrently assigned to keyring->restrict_link are for key
         * types other than dead_type. Given this, it's ok to check
         * the key type before acquiring keyring->sem.
         */
        if (!dead_type || !keyring->restrict_link ||
            keyring->restrict_link->keytype != dead_type) {
                kleave(" [no restriction gc]");
                return;
        }

        /* Lock the keyring to ensure that a link is not in progress */
        down_write(&keyring->sem);

        keyres = keyring->restrict_link;

        keyres->check = restrict_link_reject;

        key_put(keyres->key);
        keyres->key = NULL;
        keyres->keytype = NULL;

        up_write(&keyring->sem);

        kleave(" [restriction gc]");
}