使用ptrace()取消系统调用

Question

出于某些安全目的,我使用ptrace来获取系统调用号码,如果这是一个危险的调用(例如10 for unlink),我想取消这个系统调用.

这是测试程序的源代码del.c.编译gcc -o del del.c.

#include <stdio.h>
#include <stdlib.h>
int main()
{
    remove("/root/abc.out");
    return 0;
}

这是安全管理器源代码test.c.编译gcc -o test test.c.

#include <signal.h>
#include <syscall.h>
#include <sys/ptrace.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <errno.h>
#include <sys/user.h>
#include <sys/reg.h>
#include <sys/syscall.h>

int main()
{
    int i;
    pid_t child;
    int status;
    long orig_eax;
    child = fork();
    if(child == 0) {
        ptrace(PTRACE_TRACEME, 0, NULL, NULL);
        execl("/root/del", "del",  NULL);
    }
    else {
        i = 0;
        while(1){
            wait(&status);
            if (WIFEXITED(status) || WIFSIGNALED(status) )break;

            orig_eax = ptrace(PTRACE_PEEKUSER,
                          child, 4 * ORIG_EAX,
                          NULL);
            if (orig_eax == 10){
                fprintf(stderr, "Got it\n");
                kill(child, SIGKILL);
            }
            printf("%d time,"
               "system call %ld\n", i++, orig_eax);
            ptrace(PTRACE_SYSCALL, child, NULL, NULL);
        }
    }
    return 0;
}

创建abc.out文件,然后运行测试程序:

cd /root
touch abc.out
./test

该文件/root/abc.out应该仍然存在.

我该如何实现这个要求？

Answer 1

好吧似乎有时PTRACE_KILL效果不好,你可以kill改用:

if (orig_eax == 10)
{
    kill(pid, SIGKILL);
}

编辑:我用我的程序测试我的机器(Ubuntu内核3.4),一切正常:

#include <sys/ptrace.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <sys/reg.h>
#include <stdio.h>

int main(int argc, char **argv)
{   
    pid_t child;
    long orig_eax;
    int status;

    child = fork();
    if(child == 0) 
    {
        ptrace(PTRACE_TRACEME, 0, NULL, NULL);
        execl("/bin/ls", "ls", NULL);
    }
    else 
    {
        /* Both wait and waitpid works */
        //wait(NULL);
        waitpid(child, &status, 0);
        orig_eax = ptrace(PTRACE_PEEKUSER, child, 4 * ORIG_EAX, NULL);
        /* Tracking execve syscall */
        if (orig_eax == 11)
        {
            /* Both PTRACE_KILL and kill() works on my 3.4.4 Kernel */
            fprintf(stdout, "GOT IT\n");
            //ptrace(PTRACE_KILL, child, NULL, NULL);
            kill(child, SIGKILL);
        }
    }

    return 0;
}

更新:问题是您正在使用10跟踪系统调用而不是11(因为您正在执行execve命令),此代码将与您的rm命令一起使用:

if (orig_eax == 11)
{
    /* Both PTRACE_KILL and kill() works on my 3.4.4 Kernel */
    fprintf(stdout, "INSIDE THE TRAP, FILE WILL NOT BE REMOVED\n");
    ptrace(PTRACE_KILL, child, NULL, NULL);
    //kill(child, SIGKILL);
}

编辑:我尝试这个代码和所有wroks罚款(该文件abc.out执行后仍然存在CALL_REMOVE)

/*
 * REMOVE.c
 * gcc -Wall REMOVE.c -o REMOVE
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char **argv)
{
        /* Both calls work */
        //remove("/root/abc.out");
        unlink("/root/abc.out");

        return 0;
}

/*
 * CALL_REMOVE.c
 * gcc -Wall CALL_REMOVE.c -o CALL_REMOVE
 */

#include <signal.h>
#include <syscall.h>
#include <sys/ptrace.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <errno.h>
#include <sys/user.h>
#include <sys/reg.h>
#include <sys/syscall.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char **argv)
{
        int i;
        pid_t child;
        int status;
        long orig_eax;
        int kill_ret = 0;

        child = fork();

        if(child == 0)
        {
                ptrace(PTRACE_TRACEME, 0, NULL, NULL);
                execl("/root/REMOVE", "REMOVE",  NULL);
        }
        else
        {
                i = 0;
                while(1)
                {
                        wait(&status);
                        if (WIFEXITED(status) || WIFSIGNALED(status) )
                                break;

                        orig_eax = ptrace(PTRACE_PEEKUSER, child, 4 * ORIG_EAX, NULL);
                        if (orig_eax == 10)
                        {
                                fprintf(stderr, "Got it\n");
                                kill_ret = kill(child, SIGKILL);
                                if (kill_ret == -1)
                                {
                                    fprintf(stderr, "Failed to kill ---> %s\n", strerror(errno));
                                }
                        }
                        printf("%d time, system call %ld\n", i++, orig_eax);
                        ptrace(PTRACE_SYSCALL, child, NULL, NULL);
                }
        }

        return 0;
}

我们得到了这个输出:

root@UnixServer:/root# ll
total 28K
-rw-r--r-- 1 root root    6 2012-08-18 19:37 abc.out
-rw-r--r-- 1 root root 1023 2012-08-18 19:39 CALL_REMOVE.c
-rw-r--r-- 1 root root  213 2012-08-18 19:39 REMOVE.c
-rwxr-xr-x 1 root root 7,3K 2012-08-18 19:39 CALL_REMOVE
-rwxr-xr-x 1 root root 7,0K 2012-08-18 19:39 REMOVE
root@UnixServer:/root# ./CALL_REMOVE 
0 time, system call 11
1 time, system call 45
2 time, system call 45
3 time, system call 33
4 time, system call 33
5 time, system call 192
6 time, system call 192
7 time, system call 33
8 time, system call 33
9 time, system call 5
10 time, system call 5
11 time, system call 197
12 time, system call 197
13 time, system call 192
14 time, system call 192
15 time, system call 6
16 time, system call 6
17 time, system call 33
18 time, system call 33
19 time, system call 5
20 time, system call 5
21 time, system call 3
22 time, system call 3
23 time, system call 197
24 time, system call 197
25 time, system call 192
26 time, system call 192
27 time, system call 192
28 time, system call 192
29 time, system call 192
30 time, system call 192
31 time, system call 6
32 time, system call 6
33 time, system call 192
34 time, system call 192
35 time, system call 243
36 time, system call 243
37 time, system call 125
38 time, system call 125
39 time, system call 125
40 time, system call 125
41 time, system call 125
42 time, system call 125
43 time, system call 91
44 time, system call 91
Got it
45 time, system call 10
root@UnixServer:/root# ll
total 28K
-rw-r--r-- 1 root root    6 2012-08-18 19:37 abc.out
-rw-r--r-- 1 root root 1023 2012-08-18 19:39 CALL_REMOVE.c
-rw-r--r-- 1 root root  213 2012-08-18 19:39 REMOVE.c
-rwxr-xr-x 1 root root 7,3K 2012-08-18 19:39 CALL_REMOVE
-rwxr-xr-x 1 root root 7,0K 2012-08-18 19:39 REMOVE
root@UnixServer:/root#