net/ipv4/tcp_probe.c

   1 /*
   2  * tcpprobe - Observe the TCP flow with kprobes.
   3  *
   4  * The idea for this came from Werner Almesberger's umlsim
   5  * Copyright (C) 2004, Stephen Hemminger <shemminger@osdl.org>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19  */
  20
  21 #include <linux/kernel.h>
  22 #include <linux/kprobes.h>
  23 #include <linux/socket.h>
  24 #include <linux/tcp.h>
  25 #include <linux/proc_fs.h>
  26 #include <linux/module.h>
  27 #include <linux/ktime.h>
  28 #include <linux/time.h>
  29 #include <net/net_namespace.h>
  30
  31 #include <net/tcp.h>
  32
  33 MODULE_AUTHOR("Stephen Hemminger <shemminger@linux-foundation.org>");
  34 MODULE_DESCRIPTION("TCP cwnd snooper");
  35 MODULE_LICENSE("GPL");
  36 MODULE_VERSION("1.1");
  37
  38 static int port __read_mostly = 0;
  39 MODULE_PARM_DESC(port, "Port to match (0=all)");
  40 module_param(port, int, 0);
  41
  42 static unsigned int bufsize __read_mostly = 4096;
  43 MODULE_PARM_DESC(bufsize, "Log buffer size in packets (4096)");
  44 module_param(bufsize, uint, 0);
  45
  46 static int full __read_mostly;
  47 MODULE_PARM_DESC(full, "Full log (1=every ack packet received,  0=only cwnd changes)");
  48 module_param(full, int, 0);
  49
  50 static const char procname[] = "tcpprobe";
  51
  52 struct tcp_log {
  53         ktime_t tstamp;
  54         __be32  saddr, daddr;
  55         __be16  sport, dport;
  56         u16     length;
  57         u32     snd_nxt;
  58         u32     snd_una;
  59         u32     snd_wnd;
  60         u32     snd_cwnd;
  61         u32     ssthresh;
  62         u32     srtt;
  63 };
  64
  65 static struct {
  66         spinlock_t      lock;
  67         wait_queue_head_t wait;
  68         ktime_t         start;
  69         u32             lastcwnd;
  70
  71         unsigned long   head, tail;
  72         struct tcp_log  *log;
  73 } tcp_probe;
  74
  75
  76 static inline int tcp_probe_used(void)
  77 {
  78         return (tcp_probe.head - tcp_probe.tail) & (bufsize - 1);
  79 }
  80
  81 static inline int tcp_probe_avail(void)
  82 {
  83         return bufsize - tcp_probe_used() - 1;
  84 }
  85
  86 /*
  87  * Hook inserted to be called before each receive packet.
  88  * Note: arguments must match tcp_rcv_established()!
  89  */
  90 static int jtcp_rcv_established(struct sock *sk, struct sk_buff *skb,
  91                                struct tcphdr *th, unsigned len)
  92 {
  93         const struct tcp_sock *tp = tcp_sk(sk);
  94         const struct inet_sock *inet = inet_sk(sk);
  95
  96         /* Only update if port matches */
  97         if ((port == 0 || ntohs(inet->inet_dport) == port ||
  98              ntohs(inet->inet_sport) == port) &&
  99             (full || tp->snd_cwnd != tcp_probe.lastcwnd)) {
 100
 101                 spin_lock(&tcp_probe.lock);
 102                 /* If log fills, just silently drop */
 103                 if (tcp_probe_avail() > 1) {
 104                         struct tcp_log *p = tcp_probe.log + tcp_probe.head;
 105
 106                         p->tstamp = ktime_get();
 107                         p->saddr = inet->inet_saddr;
 108                         p->sport = inet->inet_sport;
 109                         p->daddr = inet->inet_daddr;
 110                         p->dport = inet->inet_dport;
 111                         p->length = skb->len;
 112                         p->snd_nxt = tp->snd_nxt;
 113                         p->snd_una = tp->snd_una;
 114                         p->snd_cwnd = tp->snd_cwnd;
 115                         p->snd_wnd = tp->snd_wnd;
 116                         p->ssthresh = tcp_current_ssthresh(sk);
 117                         p->srtt = tp->srtt >> 3;
 118
 119                         tcp_probe.head = (tcp_probe.head + 1) & (bufsize - 1);
 120                 }
 121                 tcp_probe.lastcwnd = tp->snd_cwnd;
 122                 spin_unlock(&tcp_probe.lock);
 123
 124                 wake_up(&tcp_probe.wait);
 125         }
 126
 127         jprobe_return();
 128         return 0;
 129 }
 130
 131 static struct jprobe tcp_jprobe = {
 132         .kp = {
 133                 .symbol_name    = "tcp_rcv_established",
 134         },
 135         .entry  = jtcp_rcv_established,
 136 };
 137
 138 static int tcpprobe_open(struct inode * inode, struct file * file)
 139 {
 140         /* Reset (empty) log */
 141         spin_lock_bh(&tcp_probe.lock);
 142         tcp_probe.head = tcp_probe.tail = 0;
 143         tcp_probe.start = ktime_get();
 144         spin_unlock_bh(&tcp_probe.lock);
 145
 146         return 0;
 147 }
 148
 149 static int tcpprobe_sprint(char *tbuf, int n)
 150 {
 151         const struct tcp_log *p
 152                 = tcp_probe.log + tcp_probe.tail;
 153         struct timespec tv
 154                 = ktime_to_timespec(ktime_sub(p->tstamp, tcp_probe.start));
 155
 156         return snprintf(tbuf, n,
 157                         "%lu.%09lu %pI4:%u %pI4:%u %d %#x %#x %u %u %u %u\n",
 158                         (unsigned long) tv.tv_sec,
 159                         (unsigned long) tv.tv_nsec,
 160                         &p->saddr, ntohs(p->sport),
 161                         &p->daddr, ntohs(p->dport),
 162                         p->length, p->snd_nxt, p->snd_una,
 163                         p->snd_cwnd, p->ssthresh, p->snd_wnd, p->srtt);
 164 }
 165
 166 static ssize_t tcpprobe_read(struct file *file, char __user *buf,
 167                              size_t len, loff_t *ppos)
 168 {
 169         int error = 0;
 170         size_t cnt = 0;
 171
 172         if (!buf)
 173                 return -EINVAL;
 174
 175         while (cnt < len) {
 176                 char tbuf[128];
 177                 int width;
 178
 179                 /* Wait for data in buffer */
 180                 error = wait_event_interruptible(tcp_probe.wait,
 181                                                  tcp_probe_used() > 0);
 182                 if (error)
 183                         break;
 184
 185                 spin_lock_bh(&tcp_probe.lock);
 186                 if (tcp_probe.head == tcp_probe.tail) {
 187                         /* multiple readers race? */
 188                         spin_unlock_bh(&tcp_probe.lock);
 189                         continue;
 190                 }
 191
 192                 width = tcpprobe_sprint(tbuf, sizeof(tbuf));
 193
 194                 if (cnt + width < len)
 195                         tcp_probe.tail = (tcp_probe.tail + 1) & (bufsize - 1);
 196
 197                 spin_unlock_bh(&tcp_probe.lock);
 198
 199                 /* if record greater than space available
 200                    return partial buffer (so far) */
 201                 if (cnt + width >= len)
 202                         break;
 203
 204                 if (copy_to_user(buf + cnt, tbuf, width))
 205                         return -EFAULT;
 206                 cnt += width;
 207         }
 208
 209         return cnt == 0 ? error : cnt;
 210 }
 211
 212 static const struct file_operations tcpprobe_fops = {
 213         .owner   = THIS_MODULE,
 214         .open    = tcpprobe_open,
 215         .read    = tcpprobe_read,
 216 };
 217
 218 static __init int tcpprobe_init(void)
 219 {
 220         int ret = -ENOMEM;
 221
 222         init_waitqueue_head(&tcp_probe.wait);
 223         spin_lock_init(&tcp_probe.lock);
 224
 225         if (bufsize == 0)
 226                 return -EINVAL;
 227
 228         bufsize = roundup_pow_of_two(bufsize);
 229         tcp_probe.log = kcalloc(bufsize, sizeof(struct tcp_log), GFP_KERNEL);
 230         if (!tcp_probe.log)
 231                 goto err0;
 232
 233         if (!proc_net_fops_create(&init_net, procname, S_IRUSR, &tcpprobe_fops))
 234                 goto err0;
 235
 236         ret = register_jprobe(&tcp_jprobe);
 237         if (ret)
 238                 goto err1;
 239
 240         pr_info("TCP probe registered (port=%d) bufsize=%u\n", port, bufsize);
 241         return 0;
 242  err1:
 243         proc_net_remove(&init_net, procname);
 244  err0:
 245         kfree(tcp_probe.log);
 246         return ret;
 247 }
 248 module_init(tcpprobe_init);
 249
 250 static __exit void tcpprobe_exit(void)
 251 {
 252         proc_net_remove(&init_net, procname);
 253         unregister_jprobe(&tcp_jprobe);
 254         kfree(tcp_probe.log);
 255 }
 256 module_exit(tcpprobe_exit);