linux/net/ipv4/tcp_probe.c
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   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
  34MODULE_AUTHOR("Stephen Hemminger <shemminger@linux-foundation.org>");
  35MODULE_DESCRIPTION("TCP cwnd snooper");
  36MODULE_LICENSE("GPL");
  37MODULE_VERSION("1.1");
  38
  39static int port __read_mostly = 0;
  40MODULE_PARM_DESC(port, "Port to match (0=all)");
  41module_param(port, int, 0);
  42
  43static unsigned int bufsize __read_mostly = 4096;
  44MODULE_PARM_DESC(bufsize, "Log buffer size in packets (4096)");
  45module_param(bufsize, uint, 0);
  46
  47static int full __read_mostly;
  48MODULE_PARM_DESC(full, "Full log (1=every ack packet received,  0=only cwnd changes)");
  49module_param(full, int, 0);
  50
  51static const char procname[] = "tcpprobe";
  52
  53struct 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
  66static 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
  77static inline int tcp_probe_used(void)
  78{
  79        return (tcp_probe.head - tcp_probe.tail) & (bufsize - 1);
  80}
  81
  82static 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 */
  91static 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
 132static struct jprobe tcp_jprobe = {
 133        .kp = {
 134                .symbol_name    = "tcp_rcv_established",
 135        },
 136        .entry  = jtcp_rcv_established,
 137};
 138
 139static 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
 150static 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 scnprintf(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
 167static 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[164];
 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
 213static const struct file_operations tcpprobe_fops = {
 214        .owner   = THIS_MODULE,
 215        .open    = tcpprobe_open,
 216        .read    = tcpprobe_read,
 217        .llseek  = noop_llseek,
 218};
 219
 220static __init int tcpprobe_init(void)
 221{
 222        int ret = -ENOMEM;
 223
 224        init_waitqueue_head(&tcp_probe.wait);
 225        spin_lock_init(&tcp_probe.lock);
 226
 227        if (bufsize == 0)
 228                return -EINVAL;
 229
 230        bufsize = roundup_pow_of_two(bufsize);
 231        tcp_probe.log = kcalloc(bufsize, sizeof(struct tcp_log), GFP_KERNEL);
 232        if (!tcp_probe.log)
 233                goto err0;
 234
 235        if (!proc_net_fops_create(&init_net, procname, S_IRUSR, &tcpprobe_fops))
 236                goto err0;
 237
 238        ret = register_jprobe(&tcp_jprobe);
 239        if (ret)
 240                goto err1;
 241
 242        pr_info("TCP probe registered (port=%d) bufsize=%u\n", port, bufsize);
 243        return 0;
 244 err1:
 245        proc_net_remove(&init_net, procname);
 246 err0:
 247        kfree(tcp_probe.log);
 248        return ret;
 249}
 250module_init(tcpprobe_init);
 251
 252static __exit void tcpprobe_exit(void)
 253{
 254        proc_net_remove(&init_net, procname);
 255        unregister_jprobe(&tcp_jprobe);
 256        kfree(tcp_probe.log);
 257}
 258module_exit(tcpprobe_exit);
 259
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