揭穿恶作剧重建TCP连接和进程之间的关联_tcp 连接和进程

是时候将把戏揭穿了。

请先阅读下文：
https://blog.csdn.net/dog250/article/details/108113329

依照文章中所描述的把戏，我们hack一下两个进程的tcp连接的归属，首先给出hack之前的情景：

[root@localhost ~]# netstat -ntp
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 192.168.56.110:22       192.168.56.1:55287      ESTABLISHED 1344/sshd: root@pts
tcp        0      0 192.168.56.110:22       192.168.56.1:55589      ESTABLISHED 4791/sshd: root@pts

然后，在实施hack之后，进程所属的tcp连接被交换了：

[root@localhost ~]# netstat -ntp
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 192.168.56.110:22       192.168.56.1:55287      ESTABLISHED 4791/sshd: root@pts
tcp        0      0 192.168.56.110:22       192.168.56.1:55589      ESTABLISHED 1344/sshd: root@pts

如果系统运维或者其它管理员遇到这样的情况，他们到底要瞄准哪个进程来debug呢？

注意⚠️，我们要抛弃事后的预设，事实上，他们根本无法意识到连接被交换了，等到拉了一大堆人一起开完会后很久，他们或许才能意识到事情哪里有点不对劲。

如果有我在，这种事情就不会发生，作为手艺人，我更喜欢直接面对本质，而不是使用工具迂回，在我看来，通过procfs来查找tcp连接和进程之间的关联，就是迂回。

何不直接点儿呢？

来看下面的图：

如果通过那条 不可拆除的线索 来关联tcp_sock和socket，岂不是无需迂回？

OK，下面的代码描述了如何做：

#!/usr/bin/stap -g
// tcpstat(.stp)

%{
#include <net/tcp.h>
#include <linux/fdtable.h>

struct result {
    char laddr[16];
    char raddr[16];
    unsigned short    lport;
    unsigned short    rport;
    unsigned long ino;
    int pid;
    char comm[32];
};

static inline void ip2str(char *to, unsigned int from)
{
    int size = snprintf(to, 16, "%pI4", &from);
    to[size] = '\0';
}

void traverse(struct sock *sk, unsigned long ino, struct result *ret)
{
    struct task_struct *tsk;
    int i;

    for_each_process(tsk) {
        struct file *file;
        for (i = 0; i < tsk->files->fdt->max_fds; i++) {
            file = tsk->files->fdt->fd[i];
            if (file == NULL) {
                continue;
            }
            if (file->f_inode->i_ino == ino) {
                char laddr[16], raddr[16];

                ip2str(laddr, inet_sk(sk)->inet_rcv_saddr);
                ip2str(raddr, inet_sk(sk)->inet_daddr);

                memcpy(&ret->laddr[0], laddr, 16);
                memcpy(&ret->raddr[0], raddr, 16);
                ret->lport = sk->sk_num;
                ret->rport = htons(sk->sk_dport);
                ret->ino = ino;
                ret->pid = tsk->pid;
                memcpy(&ret->comm[0], tsk->comm, 32);
            }
        }
    }
}
%}

function dump_tcp_info()
%{
    struct task_struct *tsk;
    struct inet_hashinfo *hashinfo = &tcp_hashinfo;
    struct hlist_nulls_node *node;
    struct socket_alloc *sa;
    struct sock *sk;
    struct result ret;
    int i, ino;

    for (i = 0; i < INET_LHTABLE_SIZE; i++) {
        struct inet_listen_hashbucket *ilb;

        ilb = &hashinfo->listening_hash[i];
        sk_nulls_for_each(sk, node, &ilb->head) {
            unsigned long ino;

            sa = (struct socket_alloc *)sk->sk_socket;
            ino = sa->vfs_inode.i_ino;

            traverse(sk, ino, &ret);
            STAP_PRINTF("LISTEN %s:%d  inode:%d/[%d] %s\n",
                        ret.laddr,
                        ret.lport,
                        ret.ino,
                        ret.pid,
                        ret.comm);
        }
    }

    for (i = 0; i <= hashinfo->ehash_mask; i++) {
        struct inet_ehash_bucket *head = &hashinfo->ehash[i];

        if (hlist_nulls_empty(&head->chain)) {
            continue;
        }

        sk_nulls_for_each(sk, node, &head->chain) {
            unsigned long ino;

            sa = (struct socket_alloc *)sk->sk_socket;
            ino = sa->vfs_inode.i_ino;

            traverse(sk, ino, &ret);
            STAP_PRINTF("ESTABLISHED %s:%d  %s:%d inode:%d/[%d] %s\n",
                        ret.laddr,
                        ret.lport,
                        ret.raddr,
                        ret.rport,
                        ret.ino,
                        ret.pid,
                        ret.comm);
        }
    }
%}

probe begin
{
    dump_tcp_info();
    exit();
}

来来来，我们运行上面的脚本来试一下能不能把被hack的系统真相找出来：

[root@localhost test]# ./tcpstat
LISTEN 0.0.0.0:22  inode:22852/[1001] sshd
LISTEN 0.0.0.0:22  inode:22850/[1001] sshd
ESTABLISHED 192.168.56.110:22  192.168.56.1:55287 inode:25510/[1344] sshd
ESTABLISHED 192.168.56.110:22  192.168.56.1:55589 inode:28747/[4791] sshd

用这个结果来对比一下被hack后的情形：

[root@localhost ~]# netstat -ntp
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 192.168.56.110:22       192.168.56.1:55287      ESTABLISHED 4791/sshd: root@pts
tcp        0      0 192.168.56.110:22       192.168.56.1:55589      ESTABLISHED 1344/sshd: root@pts

哈哈，真相大白！

何为手艺人？不依赖大型工具，不依赖专业知识，小镇上修锅换底而无痕迹者是也。当然，皮鞋也能做。

浙江温州皮鞋湿，下雨进水不会胖。