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/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
  33MODULE_AUTHOR("Stephen Hemminger <shemminger@linux-foundation.org>");
  34MODULE_DESCRIPTION("TCP cwnd snooper");
  35MODULE_LICENSE("GPL");
  36MODULE_VERSION("1.1");
  37
  38static int port __read_mostly = 0;
  39MODULE_PARM_DESC(port, "Port to match (0=all)");
  40module_param(port, int, 0);
  41
  42static int bufsize __read_mostly = 4096;
  43MODULE_PARM_DESC(bufsize, "Log buffer size in packets (4096)");
  44module_param(bufsize, int, 0);
  45
  46static int full __read_mostly;
  47MODULE_PARM_DESC(full, "Full log (1=every ack packet received,  0=only cwnd changes)");
  48module_param(full, int, 0);
  49
  50static const char procname[] = "tcpprobe";
  51
  52struct 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
  65static 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
  76static inline int tcp_probe_used(void)
  77{
  78        return (tcp_probe.head - tcp_probe.tail) % bufsize;
  79}
  80
  81static inline int tcp_probe_avail(void)
  82{
  83        return bufsize - tcp_probe_used();
  84}
  85
  86/*
  87 * Hook inserted to be called before each receive packet.
  88 * Note: arguments must match tcp_rcv_established()!
  89 */
  90static 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->dport) == port || ntohs(inet->sport) == port)
  98            && (full || tp->snd_cwnd != tcp_probe.lastcwnd)) {
  99
 100                spin_lock(&tcp_probe.lock);
 101                /* If log fills, just silently drop */
 102                if (tcp_probe_avail() > 1) {
 103                        struct tcp_log *p = tcp_probe.log + tcp_probe.head;
 104
 105                        p->tstamp = ktime_get();
 106                        p->saddr = inet->saddr;
 107                        p->sport = inet->sport;
 108                        p->daddr = inet->daddr;
 109                        p->dport = inet->dport;
 110                        p->length = skb->len;
 111                        p->snd_nxt = tp->snd_nxt;
 112                        p->snd_una = tp->snd_una;
 113                        p->snd_cwnd = tp->snd_cwnd;
 114                        p->snd_wnd = tp->snd_wnd;
 115                        p->ssthresh = tcp_current_ssthresh(sk);
 116                        p->srtt = tp->srtt >> 3;
 117
 118                        tcp_probe.head = (tcp_probe.head + 1) % bufsize;
 119                }
 120                tcp_probe.lastcwnd = tp->snd_cwnd;
 121                spin_unlock(&tcp_probe.lock);
 122
 123                wake_up(&tcp_probe.wait);
 124        }
 125
 126        jprobe_return();
 127        return 0;
 128}
 129
 130static struct jprobe tcp_jprobe = {
 131        .kp = {
 132                .symbol_name    = "tcp_rcv_established",
 133        },
 134        .entry  = jtcp_rcv_established,
 135};
 136
 137static int tcpprobe_open(struct inode * inode, struct file * file)
 138{
 139        /* Reset (empty) log */
 140        spin_lock_bh(&tcp_probe.lock);
 141        tcp_probe.head = tcp_probe.tail = 0;
 142        tcp_probe.start = ktime_get();
 143        spin_unlock_bh(&tcp_probe.lock);
 144
 145        return 0;
 146}
 147
 148static int tcpprobe_sprint(char *tbuf, int n)
 149{
 150        const struct tcp_log *p
 151                = tcp_probe.log + tcp_probe.tail % bufsize;
 152        struct timespec tv
 153                = ktime_to_timespec(ktime_sub(p->tstamp, tcp_probe.start));
 154
 155        return snprintf(tbuf, n,
 156                        "%lu.%09lu " NIPQUAD_FMT ":%u " NIPQUAD_FMT ":%u"
 157                        " %d %#x %#x %u %u %u %u\n",
 158                        (unsigned long) tv.tv_sec,
 159                        (unsigned long) tv.tv_nsec,
 160                        NIPQUAD(p->saddr), ntohs(p->sport),
 161                        NIPQUAD(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
 166static ssize_t tcpprobe_read(struct file *file, char __user *buf,
 167                             size_t len, loff_t *ppos)
 168{
 169        int error = 0, cnt = 0;
 170
 171        if (!buf || len < 0)
 172                return -EINVAL;
 173
 174        while (cnt < len) {
 175                char tbuf[128];
 176                int width;
 177
 178                /* Wait for data in buffer */
 179                error = wait_event_interruptible(tcp_probe.wait,
 180                                                 tcp_probe_used() > 0);
 181                if (error)
 182                        break;
 183
 184                spin_lock_bh(&tcp_probe.lock);
 185                if (tcp_probe.head == tcp_probe.tail) {
 186                        /* multiple readers race? */
 187                        spin_unlock_bh(&tcp_probe.lock);
 188                        continue;
 189                }
 190
 191                width = tcpprobe_sprint(tbuf, sizeof(tbuf));
 192
 193                if (cnt + width < len)
 194                        tcp_probe.tail = (tcp_probe.tail + 1) % bufsize;
 195
 196                spin_unlock_bh(&tcp_probe.lock);
 197
 198                /* if record greater than space available
 199                   return partial buffer (so far) */
 200                if (cnt + width >= len)
 201                        break;
 202
 203                if (copy_to_user(buf + cnt, tbuf, width))
 204                        return -EFAULT;
 205                cnt += width;
 206        }
 207
 208        return cnt == 0 ? error : cnt;
 209}
 210
 211static const struct file_operations tcpprobe_fops = {
 212        .owner   = THIS_MODULE,
 213        .open    = tcpprobe_open,
 214        .read    = tcpprobe_read,
 215};
 216
 217static __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(bufsize, sizeof(struct tcp_log), GFP_KERNEL);
 228        if (!tcp_probe.log)
 229                goto err0;
 230
 231        if (!proc_net_fops_create(&init_net, 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(&init_net, procname);
 242 err0:
 243        kfree(tcp_probe.log);
 244        return ret;
 245}
 246module_init(tcpprobe_init);
 247
 248static __exit void tcpprobe_exit(void)
 249{
 250        proc_net_remove(&init_net, procname);
 251        unregister_jprobe(&tcp_jprobe);
 252        kfree(tcp_probe.log);
 253}
 254module_exit(tcpprobe_exit);
 255
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