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POCancel a system call with ptrace()
 

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    <p>For some security purpose, I use ptrace to get the syscall number, and if it's a dangerous call (like 10 for unlink), I want to cancel this syscall.</p> <p>Here's the source code for the test program <code>del.c</code>. Compile with <code>gcc -o del del.c</code>.</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; int main() { remove("/root/abc.out"); return 0; } </code></pre> <p>Here's the security manager source code <code>test.c</code>. Compile with <code>gcc -o test test.c</code>.</p> <pre><code>#include &lt;signal.h&gt; #include &lt;syscall.h&gt; #include &lt;sys/ptrace.h&gt; #include &lt;sys/types.h&gt; #include &lt;sys/wait.h&gt; #include &lt;unistd.h&gt; #include &lt;errno.h&gt; #include &lt;sys/user.h&gt; #include &lt;sys/reg.h&gt; #include &lt;sys/syscall.h&gt; 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(&amp;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; } </code></pre> <p>Create the <code>abc.out</code> file, then run the test program:</p> <pre class="lang-sh prettyprint-override"><code>cd /root touch abc.out ./test </code></pre> <p>The file <code>/root/abc.out</code> should still exist.</p> <p>How do I implement this requirement?</p>
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    1. COAre you doing anything to force the forked process to wait to see whether or not your security manager is going to kill it? As I understand it, `waitpid()` is going to make the current process wait until the forked process terminates. So of course you will not be able to stop the system-call. By the time you're able to get the system-call code, the forked process has already executed it.
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    2. CO@aroth, I sure `waitpid()` works, My problem is how to cancel the sys_call?
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