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/slab.h>
  26 #include <linux/proc_fs.h>
  27 #include <linux/module.h>
  28 #include <linux/ktime.h>
  29 #include <linux/time.h>
  30 #include <net/net_namespace.h>
  31
  32 #include <net/tcp.h>
  33
  34 MODULE_AUTHOR("Stephen Hemminger <shemminger@linux-foundation.org>");
  35 MODULE_DESCRIPTION("TCP cwnd snooper");
  36 MODULE_LICENSE("GPL");
  37 MODULE_VERSION("1.1");
  38
  39 static int port __read_mostly = 0;
  40 MODULE_PARM_DESC(port, "Port to match (0=all)");
  41 module_param(port, int, 0);
  42
  43 static unsigned int bufsize __read_mostly = 4096;
  44 MODULE_PARM_DESC(bufsize, "Log buffer size in packets (4096)");
  45 module_param(bufsize, uint, 0);
  46
  47 static int full __read_mostly;
  48 MODULE_PARM_DESC(full, "Full log (1=every ack packet received,  0=only cwnd changes)");
  49 module_param(full, int, 0);
  50
  51 static const char procname[] = "tcpprobe";
  52
  53 struct tcp_log {
  54         ktime_t tstamp;
  55         __be32  saddr, daddr;
  56         __be16  sport, dport;
  57         u16     length;
  58         u32     snd_nxt;
  59         u32     snd_una;
  60         u32     snd_wnd;
  61         u32     snd_cwnd;
  62         u32     ssthresh;
  63         u32     srtt;
  64 };
  65
  66 static struct {
  67         spinlock_t      lock;
  68         wait_queue_head_t wait;
  69         ktime_t         start;
  70         u32             lastcwnd;
  71
  72         unsigned long   head, tail;
  73         struct tcp_log  *log;
  74 } tcp_probe;
  75
  76
  77 static inline int tcp_probe_used(void)
  78 {
  79         return (tcp_probe.head - tcp_probe.tail) & (bufsize - 1);
  80 }
  81
  82 static inline int tcp_probe_avail(void)
  83 {
  84         return bufsize - tcp_probe_used() - 1;
  85 }
  86
  87 /*
  88  * Hook inserted to be called before each receive packet.
  89  * Note: arguments must match tcp_rcv_established()!
  90  */
  91 static int jtcp_rcv_established(struct sock *sk, struct sk_buff *skb,
  92                                struct tcphdr *th, unsigned len)
  93 {
  94         const struct tcp_sock *tp = tcp_sk(sk);
  95         const struct inet_sock *inet = inet_sk(sk);
  96
  97         /* Only update if port matches */
  98         if ((port == 0 || ntohs(inet->inet_dport) == port ||
  99              ntohs(inet->inet_sport) == port) &&
 100             (full || tp->snd_cwnd != tcp_probe.lastcwnd)) {
 101
 102                 spin_lock(&tcp_probe.lock);
 103                 /* If log fills, just silently drop */
 104                 if (tcp_probe_avail() > 1) {
 105                         struct tcp_log *p = tcp_probe.log + tcp_probe.head;
 106
 107                         p->tstamp = ktime_get();
 108                         p->saddr = inet->inet_saddr;
 109                         p->sport = inet->inet_sport;
 110                         p->daddr = inet->inet_daddr;
 111                         p->dport = inet->inet_dport;
 112                         p->length = skb->len;
 113                         p->snd_nxt = tp->snd_nxt;
 114                         p->snd_una = tp->snd_una;
 115                         p->snd_cwnd = tp->snd_cwnd;
 116                         p->snd_wnd = tp->snd_wnd;
 117                         p->ssthresh = tcp_current_ssthresh(sk);
 118                         p->srtt = tp->srtt >> 3;
 119
 120                         tcp_probe.head = (tcp_probe.head + 1) & (bufsize - 1);
 121                 }
 122                 tcp_probe.lastcwnd = tp->snd_cwnd;
 123                 spin_unlock(&tcp_probe.lock);
 124
 125                 wake_up(&tcp_probe.wait);
 126         }
 127
 128         jprobe_return();
 129         return 0;
 130 }
 131
 132 static struct jprobe tcp_jprobe = {
 133         .kp = {
 134                 .symbol_name    = "tcp_rcv_established",
 135         },
 136         .entry  = jtcp_rcv_established,
 137 };
 138
 139 static int tcpprobe_open(struct inode * inode, struct file * file)
 140 {
 141         /* Reset (empty) log */
 142         spin_lock_bh(&tcp_probe.lock);
 143         tcp_probe.head = tcp_probe.tail = 0;
 144         tcp_probe.start = ktime_get();
 145         spin_unlock_bh(&tcp_probe.lock);
 146
 147         return 0;
 148 }
 149
 150 static int tcpprobe_sprint(char *tbuf, int n)
 151 {
 152         const struct tcp_log *p
 153                 = tcp_probe.log + tcp_probe.tail;
 154         struct timespec tv
 155                 = ktime_to_timespec(ktime_sub(p->tstamp, tcp_probe.start));
 156
 157         return snprintf(tbuf, n,
 158                         "%lu.%09lu %pI4:%u %pI4:%u %d %#x %#x %u %u %u %u\n",
 159                         (unsigned long) tv.tv_sec,
 160                         (unsigned long) tv.tv_nsec,
 161                         &p->saddr, ntohs(p->sport),
 162                         &p->daddr, ntohs(p->dport),
 163                         p->length, p->snd_nxt, p->snd_una,
 164                         p->snd_cwnd, p->ssthresh, p->snd_wnd, p->srtt);
 165 }
 166
 167 static ssize_t tcpprobe_read(struct file *file, char __user *buf,
 168                              size_t len, loff_t *ppos)
 169 {
 170         int error = 0;
 171         size_t cnt = 0;
 172
 173         if (!buf)
 174                 return -EINVAL;
 175
 176         while (cnt < len) {
 177                 char tbuf[128];
 178                 int width;
 179
 180                 /* Wait for data in buffer */
 181                 error = wait_event_interruptible(tcp_probe.wait,
 182                                                  tcp_probe_used() > 0);
 183                 if (error)
 184                         break;
 185
 186                 spin_lock_bh(&tcp_probe.lock);
 187                 if (tcp_probe.head == tcp_probe.tail) {
 188                         /* multiple readers race? */
 189                         spin_unlock_bh(&tcp_probe.lock);
 190                         continue;
 191                 }
 192
 193                 width = tcpprobe_sprint(tbuf, sizeof(tbuf));
 194
 195                 if (cnt + width < len)
 196                         tcp_probe.tail = (tcp_probe.tail + 1) & (bufsize - 1);
 197
 198                 spin_unlock_bh(&tcp_probe.lock);
 199
 200                 /* if record greater than space available
 201                    return partial buffer (so far) */
 202                 if (cnt + width >= len)
 203                         break;
 204
 205                 if (copy_to_user(buf + cnt, tbuf, width))
 206                         return -EFAULT;
 207                 cnt += width;
 208         }
 209
 210         return cnt == 0 ? error : cnt;
 211 }
 212
 213 static const struct file_operations tcpprobe_fops = {
 214         .owner   = THIS_MODULE,
 215         .open    = tcpprobe_open,
 216         .read    = tcpprobe_read,
 217 };
 218
 219 static __init int tcpprobe_init(void)
 220 {
 221         int ret = -ENOMEM;
 222
 223         init_waitqueue_head(&tcp_probe.wait);
 224         spin_lock_init(&tcp_probe.lock);
 225
 226         if (bufsize == 0)
 227                 return -EINVAL;
 228
 229         bufsize = roundup_pow_of_two(bufsize);
 230         tcp_probe.log = kcalloc(bufsize, sizeof(struct tcp_log), GFP_KERNEL);
 231         if (!tcp_probe.log)
 232                 goto err0;
 233
 234         if (!proc_net_fops_create(&init_net, procname, S_IRUSR, &tcpprobe_fops))
 235                 goto err0;
 236
 237         ret = register_jprobe(&tcp_jprobe);
 238         if (ret)
 239                 goto err1;
 240
 241         pr_info("TCP probe registered (port=%d) bufsize=%u\n", port, bufsize);
 242         return 0;
 243  err1:
 244         proc_net_remove(&init_net, procname);
 245  err0:
 246         kfree(tcp_probe.log);
 247         return ret;
 248 }
 249 module_init(tcpprobe_init);
 250
 251 static __exit void tcpprobe_exit(void)
 252 {
 253         proc_net_remove(&init_net, procname);
 254         unregister_jprobe(&tcp_jprobe);
 255         kfree(tcp_probe.log);
 256 }
 257 module_exit(tcpprobe_exit);