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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  22
  23 #include <linux/kernel.h>
  24 #include <linux/kprobes.h>
  25 #include <linux/socket.h>
  26 #include <linux/tcp.h>
  27 #include <linux/slab.h>
  28 #include <linux/proc_fs.h>
  29 #include <linux/module.h>
  30 #include <linux/ktime.h>
  31 #include <linux/time.h>
  32 #include <net/net_namespace.h>
  33
  34 #include <net/tcp.h>
  35
  36 MODULE_AUTHOR("Stephen Hemminger <shemminger@linux-foundation.org>");
  37 MODULE_DESCRIPTION("TCP cwnd snooper");
  38 MODULE_LICENSE("GPL");
  39 MODULE_VERSION("1.1");
  40
  41 static int port __read_mostly = 0;
  42 MODULE_PARM_DESC(port, "Port to match (0=all)");
  43 module_param(port, int, 0);
  44
  45 static unsigned int bufsize __read_mostly = 4096;
  46 MODULE_PARM_DESC(bufsize, "Log buffer size in packets (4096)");
  47 module_param(bufsize, uint, 0);
  48
  49 static int full __read_mostly;
  50 MODULE_PARM_DESC(full, "Full log (1=every ack packet received,  0=only cwnd changes)");
  51 module_param(full, int, 0);
  52
  53 static const char procname[] = "tcpprobe";
  54
  55 struct tcp_log {
  56         ktime_t tstamp;
  57         __be32  saddr, daddr;
  58         __be16  sport, dport;
  59         u16     length;
  60         u32     snd_nxt;
  61         u32     snd_una;
  62         u32     snd_wnd;
  63         u32     snd_cwnd;
  64         u32     ssthresh;
  65         u32     srtt;
  66 };
  67
  68 static struct {
  69         spinlock_t      lock;
  70         wait_queue_head_t wait;
  71         ktime_t         start;
  72         u32             lastcwnd;
  73
  74         unsigned long   head, tail;
  75         struct tcp_log  *log;
  76 } tcp_probe;
  77
  78
  79 static inline int tcp_probe_used(void)
  80 {
  81         return (tcp_probe.head - tcp_probe.tail) & (bufsize - 1);
  82 }
  83
  84 static inline int tcp_probe_avail(void)
  85 {
  86         return bufsize - tcp_probe_used() - 1;
  87 }
  88
  89 /*
  90  * Hook inserted to be called before each receive packet.
  91  * Note: arguments must match tcp_rcv_established()!
  92  */
  93 static int jtcp_rcv_established(struct sock *sk, struct sk_buff *skb,
  94                                struct tcphdr *th, unsigned int len)
  95 {
  96         const struct tcp_sock *tp = tcp_sk(sk);
  97         const struct inet_sock *inet = inet_sk(sk);
  98
  99         /* Only update if port matches */
 100         if ((port == 0 || ntohs(inet->inet_dport) == port ||
 101              ntohs(inet->inet_sport) == port) &&
 102             (full || tp->snd_cwnd != tcp_probe.lastcwnd)) {
 103
 104                 spin_lock(&tcp_probe.lock);
 105                 /* If log fills, just silently drop */
 106                 if (tcp_probe_avail() > 1) {
 107                         struct tcp_log *p = tcp_probe.log + tcp_probe.head;
 108
 109                         p->tstamp = ktime_get();
 110                         p->saddr = inet->inet_saddr;
 111                         p->sport = inet->inet_sport;
 112                         p->daddr = inet->inet_daddr;
 113                         p->dport = inet->inet_dport;
 114                         p->length = skb->len;
 115                         p->snd_nxt = tp->snd_nxt;
 116                         p->snd_una = tp->snd_una;
 117                         p->snd_cwnd = tp->snd_cwnd;
 118                         p->snd_wnd = tp->snd_wnd;
 119                         p->ssthresh = tcp_current_ssthresh(sk);
 120                         p->srtt = tp->srtt >> 3;
 121
 122                         tcp_probe.head = (tcp_probe.head + 1) & (bufsize - 1);
 123                 }
 124                 tcp_probe.lastcwnd = tp->snd_cwnd;
 125                 spin_unlock(&tcp_probe.lock);
 126
 127                 wake_up(&tcp_probe.wait);
 128         }
 129
 130         jprobe_return();
 131         return 0;
 132 }
 133
 134 static struct jprobe tcp_jprobe = {
 135         .kp = {
 136                 .symbol_name    = "tcp_rcv_established",
 137         },
 138         .entry  = jtcp_rcv_established,
 139 };
 140
 141 static int tcpprobe_open(struct inode *inode, struct file *file)
 142 {
 143         /* Reset (empty) log */
 144         spin_lock_bh(&tcp_probe.lock);
 145         tcp_probe.head = tcp_probe.tail = 0;
 146         tcp_probe.start = ktime_get();
 147         spin_unlock_bh(&tcp_probe.lock);
 148
 149         return 0;
 150 }
 151
 152 static int tcpprobe_sprint(char *tbuf, int n)
 153 {
 154         const struct tcp_log *p
 155                 = tcp_probe.log + tcp_probe.tail;
 156         struct timespec tv
 157                 = ktime_to_timespec(ktime_sub(p->tstamp, tcp_probe.start));
 158
 159         return scnprintf(tbuf, n,
 160                         "%lu.%09lu %pI4:%u %pI4:%u %d %#x %#x %u %u %u %u\n",
 161                         (unsigned long) tv.tv_sec,
 162                         (unsigned long) tv.tv_nsec,
 163                         &p->saddr, ntohs(p->sport),
 164                         &p->daddr, ntohs(p->dport),
 165                         p->length, p->snd_nxt, p->snd_una,
 166                         p->snd_cwnd, p->ssthresh, p->snd_wnd, p->srtt);
 167 }
 168
 169 static ssize_t tcpprobe_read(struct file *file, char __user *buf,
 170                              size_t len, loff_t *ppos)
 171 {
 172         int error = 0;
 173         size_t cnt = 0;
 174
 175         if (!buf)
 176                 return -EINVAL;
 177
 178         while (cnt < len) {
 179                 char tbuf[164];
 180                 int width;
 181
 182                 /* Wait for data in buffer */
 183                 error = wait_event_interruptible(tcp_probe.wait,
 184                                                  tcp_probe_used() > 0);
 185                 if (error)
 186                         break;
 187
 188                 spin_lock_bh(&tcp_probe.lock);
 189                 if (tcp_probe.head == tcp_probe.tail) {
 190                         /* multiple readers race? */
 191                         spin_unlock_bh(&tcp_probe.lock);
 192                         continue;
 193                 }
 194
 195                 width = tcpprobe_sprint(tbuf, sizeof(tbuf));
 196
 197                 if (cnt + width < len)
 198                         tcp_probe.tail = (tcp_probe.tail + 1) & (bufsize - 1);
 199
 200                 spin_unlock_bh(&tcp_probe.lock);
 201
 202                 /* if record greater than space available
 203                    return partial buffer (so far) */
 204                 if (cnt + width >= len)
 205                         break;
 206
 207                 if (copy_to_user(buf + cnt, tbuf, width))
 208                         return -EFAULT;
 209                 cnt += width;
 210         }
 211
 212         return cnt == 0 ? error : cnt;
 213 }
 214
 215 static const struct file_operations tcpprobe_fops = {
 216         .owner   = THIS_MODULE,
 217         .open    = tcpprobe_open,
 218         .read    = tcpprobe_read,
 219         .llseek  = noop_llseek,
 220 };
 221
 222 static __init int tcpprobe_init(void)
 223 {
 224         int ret = -ENOMEM;
 225
 226         init_waitqueue_head(&tcp_probe.wait);
 227         spin_lock_init(&tcp_probe.lock);
 228
 229         if (bufsize == 0)
 230                 return -EINVAL;
 231
 232         bufsize = roundup_pow_of_two(bufsize);
 233         tcp_probe.log = kcalloc(bufsize, sizeof(struct tcp_log), GFP_KERNEL);
 234         if (!tcp_probe.log)
 235                 goto err0;
 236
 237         if (!proc_net_fops_create(&init_net, procname, S_IRUSR, &tcpprobe_fops))
 238                 goto err0;
 239
 240         ret = register_jprobe(&tcp_jprobe);
 241         if (ret)
 242                 goto err1;
 243
 244         pr_info("probe registered (port=%d) bufsize=%u\n", port, bufsize);
 245         return 0;
 246  err1:
 247         proc_net_remove(&init_net, procname);
 248  err0:
 249         kfree(tcp_probe.log);
 250         return ret;
 251 }
 252 module_init(tcpprobe_init);
 253
 254 static __exit void tcpprobe_exit(void)
 255 {
 256         proc_net_remove(&init_net, procname);
 257         unregister_jprobe(&tcp_jprobe);
 258         kfree(tcp_probe.log);
 259 }
 260 module_exit(tcpprobe_exit);