tcp_probe.c

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/*
 * tcpprobe - Observe the TCP flow with kprobes.
 *
 * The idea for this came from Werner Almesberger's umlsim
 * Copyright (C) 2004, Stephen Hemminger <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/socket.h>
#include <linux/tcp.h>
#include <linux/slab.h>
#include <linux/proc_fs.h>
#include <linux/module.h>
#include <linux/ktime.h>
#include <linux/time.h>
#include <net/net_namespace.h>

#include <net/tcp.h>

MODULE_AUTHOR("Stephen Hemminger <[email protected]>");
MODULE_DESCRIPTION("TCP cwnd snooper");
MODULE_LICENSE("GPL");
MODULE_VERSION("1.1");

static int port __read_mostly = 0;
MODULE_PARM_DESC(port, "Port to match (0=all)");
module_param(port, int, 0);

static unsigned int bufsize __read_mostly = 4096;
MODULE_PARM_DESC(bufsize, "Log buffer size in packets (4096)");
module_param(bufsize, uint, 0);

static int full __read_mostly;
MODULE_PARM_DESC(full, "Full log (1=every ack packet received,  0=only cwnd changes)");
module_param(full, int, 0);

static const char procname[] = "tcpprobe";

struct tcp_log {
    ktime_t tstamp;
    __be32  saddr, daddr;
    __be16  sport, dport;
    u16 length;
    u32 snd_nxt;
    u32 snd_una;
    u32 snd_wnd;
    u32 snd_cwnd;
    u32 ssthresh;
    u32 srtt;
};

static struct {
    spinlock_t  lock;
    wait_queue_head_t wait;
    ktime_t     start;
    u32     lastcwnd;

    unsigned long   head, tail;
    struct tcp_log  *log;
} tcp_probe;


static inline int tcp_probe_used(void)
{
    return (tcp_probe.head - tcp_probe.tail) & (bufsize - 1);
}

static inline int tcp_probe_avail(void)
{
    return bufsize - tcp_probe_used() - 1;
}

/*
 * Hook inserted to be called before each receive packet.
 * Note: arguments must match tcp_rcv_established()!
 */
static int jtcp_rcv_established(struct sock *sk, struct sk_buff *skb,
                   struct tcphdr *th, unsigned int len)
{
    const struct tcp_sock *tp = tcp_sk(sk);
    const struct inet_sock *inet = inet_sk(sk);

    /* Only update if port matches */
    if ((port == 0 || ntohs(inet->inet_dport) == port ||
         ntohs(inet->inet_sport) == port) &&
        (full || tp->snd_cwnd != tcp_probe.lastcwnd)) {

        spin_lock(&tcp_probe.lock);
        /* If log fills, just silently drop */
        if (tcp_probe_avail() > 1) {
            struct tcp_log *p = tcp_probe.log + tcp_probe.head;

            p->tstamp = ktime_get();
            p->saddr = inet->inet_saddr;
            p->sport = inet->inet_sport;
            p->daddr = inet->inet_daddr;
            p->dport = inet->inet_dport;
            p->length = skb->len;
            p->snd_nxt = tp->snd_nxt;
            p->snd_una = tp->snd_una;
            p->snd_cwnd = tp->snd_cwnd;
            p->snd_wnd = tp->snd_wnd;
            p->ssthresh = tcp_current_ssthresh(sk);
            p->srtt = tp->srtt >> 3;

            tcp_probe.head = (tcp_probe.head + 1) & (bufsize - 1);
        }
        tcp_probe.lastcwnd = tp->snd_cwnd;
        spin_unlock(&tcp_probe.lock);

        wake_up(&tcp_probe.wait);
    }

    jprobe_return();
    return 0;
}

static struct jprobe tcp_jprobe = {
    .kp = {
        .symbol_name    = "tcp_rcv_established",
    },
    .entry  = jtcp_rcv_established,
};

static int tcpprobe_open(struct inode *inode, struct file *file)
{
    /* Reset (empty) log */
    spin_lock_bh(&tcp_probe.lock);
    tcp_probe.head = tcp_probe.tail = 0;
    tcp_probe.start = ktime_get();
    spin_unlock_bh(&tcp_probe.lock);

    return 0;
}

static int tcpprobe_sprint(char *tbuf, int n)
{
    const struct tcp_log *p
        = tcp_probe.log + tcp_probe.tail;
    struct timespec tv
        = ktime_to_timespec(ktime_sub(p->tstamp, tcp_probe.start));

    return scnprintf(tbuf, n,
            "%lu.%09lu %pI4:%u %pI4:%u %d %#x %#x %u %u %u %u\n",
            (unsigned long) tv.tv_sec,
            (unsigned long) tv.tv_nsec,
            &p->saddr, ntohs(p->sport),
            &p->daddr, ntohs(p->dport),
            p->length, p->snd_nxt, p->snd_una,
            p->snd_cwnd, p->ssthresh, p->snd_wnd, p->srtt);
}

static ssize_t tcpprobe_read(struct file *file, char __user *buf,
                 size_t len, loff_t *ppos)
{
    int error = 0;
    size_t cnt = 0;

    if (!buf)
        return -EINVAL;

    while (cnt < len) {
        char tbuf[164];
        int width;

        /* Wait for data in buffer */
        error = wait_event_interruptible(tcp_probe.wait,
                         tcp_probe_used() > 0);
        if (error)
            break;

        spin_lock_bh(&tcp_probe.lock);
        if (tcp_probe.head == tcp_probe.tail) {
            /* multiple readers race? */
            spin_unlock_bh(&tcp_probe.lock);
            continue;
        }

        width = tcpprobe_sprint(tbuf, sizeof(tbuf));

        if (cnt + width < len)
            tcp_probe.tail = (tcp_probe.tail + 1) & (bufsize - 1);

        spin_unlock_bh(&tcp_probe.lock);

        /* if record greater than space available
           return partial buffer (so far) */
        if (cnt + width >= len)
            break;

        if (copy_to_user(buf + cnt, tbuf, width))
            return -EFAULT;
        cnt += width;
    }

    return cnt == 0 ? error : cnt;
}

static const struct file_operations tcpprobe_fops = {
    .owner   = THIS_MODULE,
    .open    = tcpprobe_open,
    .read    = tcpprobe_read,
    .llseek  = noop_llseek,
};

static __init int tcpprobe_init(void)
{
    int ret = -ENOMEM;

    init_waitqueue_head(&tcp_probe.wait);
    spin_lock_init(&tcp_probe.lock);

    if (bufsize == 0)
        return -EINVAL;

    bufsize = roundup_pow_of_two(bufsize);
    tcp_probe.log = kcalloc(bufsize, sizeof(struct tcp_log), GFP_KERNEL);
    if (!tcp_probe.log)
        goto err0;

    if (!proc_net_fops_create(&init_net, procname, S_IRUSR, &tcpprobe_fops))
        goto err0;

    ret = register_jprobe(&tcp_jprobe);
    if (ret)
        goto err1;

    pr_info("probe registered (port=%d) bufsize=%u\n", port, bufsize);
    return 0;
 err1:
    proc_net_remove(&init_net, procname);
 err0:
    kfree(tcp_probe.log);
    return ret;
}
module_init(tcpprobe_init);

static __exit void tcpprobe_exit(void)
{
    proc_net_remove(&init_net, procname);
    unregister_jprobe(&tcp_jprobe);
    kfree(tcp_probe.log);
}
module_exit(tcpprobe_exit);