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#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
  36MODULE_AUTHOR("Stephen Hemminger <shemminger@linux-foundation.org>");
  37MODULE_DESCRIPTION("TCP cwnd snooper");
  38MODULE_LICENSE("GPL");
  39MODULE_VERSION("1.1");
  40
  41static int port __read_mostly = 0;
  42MODULE_PARM_DESC(port, "Port to match (0=all)");
  43module_param(port, int, 0);
  44
  45static unsigned int bufsize __read_mostly = 4096;
  46MODULE_PARM_DESC(bufsize, "Log buffer size in packets (4096)");
  47module_param(bufsize, uint, 0);
  48
  49static int full __read_mostly;
  50MODULE_PARM_DESC(full, "Full log (1=every ack packet received,  0=only cwnd changes)");
  51module_param(full, int, 0);
  52
  53static const char procname[] = "tcpprobe";
  54
  55struct 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
  68static 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
  79static inline int tcp_probe_used(void)
  80{
  81        return (tcp_probe.head - tcp_probe.tail) & (bufsize - 1);
  82}
  83
  84static 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 */
  93static 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
 134static struct jprobe tcp_jprobe = {
 135        .kp = {
 136                .symbol_name    = "tcp_rcv_established",
 137        },
 138        .entry  = jtcp_rcv_established,
 139};
 140
 141static 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
 152static 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
 169static 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
 215static const struct file_operations tcpprobe_fops = {
 216        .owner   = THIS_MODULE,
 217        .open    = tcpprobe_open,
 218        .read    = tcpprobe_read,
 219        .llseek  = noop_llseek,
 220};
 221
 222static __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}
 252module_init(tcpprobe_init);
 253
 254static __exit void tcpprobe_exit(void)
 255{
 256        proc_net_remove(&init_net, procname);
 257        unregister_jprobe(&tcp_jprobe);
 258        kfree(tcp_probe.log);
 259}
 260module_exit(tcpprobe_exit);
 261
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