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
  30 #include <net/tcp.h>
  31
  32 MODULE_AUTHOR("Stephen Hemminger <shemminger@linux-foundation.org>");
  33 MODULE_DESCRIPTION("TCP cwnd snooper");
  34 MODULE_LICENSE("GPL");
  35 MODULE_VERSION("1.1");
  36
  37 static int port __read_mostly = 0;
  38 MODULE_PARM_DESC(port, "Port to match (0=all)");
  39 module_param(port, int, 0);
  40
  41 static int bufsize __read_mostly = 4096;
  42 MODULE_PARM_DESC(bufsize, "Log buffer size in packets (4096)");
  43 module_param(bufsize, int, 0);
  44
  45 static int full __read_mostly;
  46 MODULE_PARM_DESC(full, "Full log (1=every ack packet received,  0=only cwnd changes)");
  47 module_param(full, int, 0);
  48
  49 static const char procname[] = "tcpprobe";
  50
  51 struct tcp_log {
  52         ktime_t tstamp;
  53         __be32  saddr, daddr;
  54         __be16  sport, dport;
  55         u16     length;
  56         u32     snd_nxt;
  57         u32     snd_una;
  58         u32     snd_wnd;
  59         u32     snd_cwnd;
  60         u32     ssthresh;
  61         u32     srtt;
  62 };
  63
  64 static struct {
  65         spinlock_t      lock;
  66         wait_queue_head_t wait;
  67         ktime_t         start;
  68         u32             lastcwnd;
  69
  70         unsigned long   head, tail;
  71         struct tcp_log  *log;
  72 } tcp_probe;
  73
  74
  75 static inline int tcp_probe_used(void)
  76 {
  77         return (tcp_probe.head - tcp_probe.tail) % bufsize;
  78 }
  79
  80 static inline int tcp_probe_avail(void)
  81 {
  82         return bufsize - tcp_probe_used();
  83 }
  84
  85 /*
  86  * Hook inserted to be called before each receive packet.
  87  * Note: arguments must match tcp_rcv_established()!
  88  */
  89 static int jtcp_rcv_established(struct sock *sk, struct sk_buff *skb,
  90                                struct tcphdr *th, unsigned len)
  91 {
  92         const struct tcp_sock *tp = tcp_sk(sk);
  93         const struct inet_sock *inet = inet_sk(sk);
  94
  95         /* Only update if port matches */
  96         if ((port == 0 || ntohs(inet->dport) == port || ntohs(inet->sport) == port)
  97             && (full || tp->snd_cwnd != tcp_probe.lastcwnd)) {
  98
  99                 spin_lock(&tcp_probe.lock);
 100                 /* If log fills, just silently drop */
 101                 if (tcp_probe_avail() > 1) {
 102                         struct tcp_log *p = tcp_probe.log + tcp_probe.head;
 103
 104                         p->tstamp = ktime_get();
 105                         p->saddr = inet->saddr;
 106                         p->sport = inet->sport;
 107                         p->daddr = inet->daddr;
 108                         p->dport = inet->dport;
 109                         p->length = skb->len;
 110                         p->snd_nxt = tp->snd_nxt;
 111                         p->snd_una = tp->snd_una;
 112                         p->snd_cwnd = tp->snd_cwnd;
 113                         p->snd_wnd = tp->snd_wnd;
 114                         p->ssthresh = tcp_current_ssthresh(sk);
 115                         p->srtt = tp->srtt >> 3;
 116
 117                         tcp_probe.head = (tcp_probe.head + 1) % bufsize;
 118                 }
 119                 tcp_probe.lastcwnd = tp->snd_cwnd;
 120                 spin_unlock(&tcp_probe.lock);
 121
 122                 wake_up(&tcp_probe.wait);
 123         }
 124
 125         jprobe_return();
 126         return 0;
 127 }
 128
 129 static struct jprobe tcp_jprobe = {
 130         .kp = {
 131                 .symbol_name    = "tcp_rcv_established",
 132         },
 133         .entry  = jtcp_rcv_established,
 134 };
 135
 136 static int tcpprobe_open(struct inode * inode, struct file * file)
 137 {
 138         /* Reset (empty) log */
 139         spin_lock_bh(&tcp_probe.lock);
 140         tcp_probe.head = tcp_probe.tail = 0;
 141         tcp_probe.start = ktime_get();
 142         spin_unlock_bh(&tcp_probe.lock);
 143
 144         return 0;
 145 }
 146
 147 static int tcpprobe_sprint(char *tbuf, int n)
 148 {
 149         const struct tcp_log *p
 150                 = tcp_probe.log + tcp_probe.tail % bufsize;
 151         struct timespec tv
 152                 = ktime_to_timespec(ktime_sub(p->tstamp, tcp_probe.start));
 153
 154         return snprintf(tbuf, n,
 155                         "%lu.%09lu %d.%d.%d.%d:%u %d.%d.%d.%d:%u"
 156                         " %d %#x %#x %u %u %u %u\n",
 157                         (unsigned long) tv.tv_sec,
 158                         (unsigned long) tv.tv_nsec,
 159                         NIPQUAD(p->saddr), ntohs(p->sport),
 160                         NIPQUAD(p->daddr), ntohs(p->dport),
 161                         p->length, p->snd_nxt, p->snd_una,
 162                         p->snd_cwnd, p->ssthresh, p->snd_wnd, p->srtt);
 163 }
 164
 165 static ssize_t tcpprobe_read(struct file *file, char __user *buf,
 166                              size_t len, loff_t *ppos)
 167 {
 168         int error = 0, cnt = 0;
 169
 170         if (!buf || len < 0)
 171                 return -EINVAL;
 172
 173         while (cnt < len) {
 174                 char tbuf[128];
 175                 int width;
 176
 177                 /* Wait for data in buffer */
 178                 error = wait_event_interruptible(tcp_probe.wait,
 179                                                  tcp_probe_used() > 0);
 180                 if (error)
 181                         break;
 182
 183                 spin_lock_bh(&tcp_probe.lock);
 184                 if (tcp_probe.head == tcp_probe.tail) {
 185                         /* multiple readers race? */
 186                         spin_unlock_bh(&tcp_probe.lock);
 187                         continue;
 188                 }
 189
 190                 width = tcpprobe_sprint(tbuf, sizeof(tbuf));
 191
 192                 if (width < len)
 193                         tcp_probe.tail = (tcp_probe.tail + 1) % bufsize;
 194
 195                 spin_unlock_bh(&tcp_probe.lock);
 196
 197                 /* if record greater than space available
 198                    return partial buffer (so far) */
 199                 if (width >= len)
 200                         break;
 201
 202                 error = copy_to_user(buf + cnt, tbuf, width);
 203                 if (error)
 204                         break;
 205                 cnt += width;
 206         }
 207
 208         return cnt == 0 ? error : cnt;
 209 }
 210
 211 static const struct file_operations tcpprobe_fops = {
 212         .owner   = THIS_MODULE,
 213         .open    = tcpprobe_open,
 214         .read    = tcpprobe_read,
 215 };
 216
 217 static __init int tcpprobe_init(void)
 218 {
 219         int ret = -ENOMEM;
 220
 221         init_waitqueue_head(&tcp_probe.wait);
 222         spin_lock_init(&tcp_probe.lock);
 223
 224         if (bufsize < 0)
 225                 return -EINVAL;
 226
 227         tcp_probe.log = kcalloc(sizeof(struct tcp_log), bufsize, GFP_KERNEL);
 228         if (!tcp_probe.log)
 229                 goto err0;
 230
 231         if (!proc_net_fops_create(procname, S_IRUSR, &tcpprobe_fops))
 232                 goto err0;
 233
 234         ret = register_jprobe(&tcp_jprobe);
 235         if (ret)
 236                 goto err1;
 237
 238         pr_info("TCP probe registered (port=%d)\n", port);
 239         return 0;
 240  err1:
 241         proc_net_remove(procname);
 242  err0:
 243         kfree(tcp_probe.log);
 244         return ret;
 245 }
 246 module_init(tcpprobe_init);
 247
 248 static __exit void tcpprobe_exit(void)
 249 {
 250         proc_net_remove(procname);
 251         unregister_jprobe(&tcp_jprobe);
 252         kfree(tcp_probe.log);
 253 }
 254 module_exit(tcpprobe_exit);