Messages in this thread Patch in this message | | | Date | Mon, 23 May 2011 19:05:28 +0200 | From | Oleg Nesterov <> | Subject | [PATCH 1/2] ptrace: ptrace_resume() shouldn't wake up !TASK_TRACED thread |
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It is not clear why ptrace_resume() does wake_up_process(). Unless the caller is PTRACE_KILL the tracee should be TASK_TRACED so we can use wake_up_state(__TASK_TRACED). If sys_ptrace() races with SIGKILL we do not need the extra and potentionally spurious wakeup.
If the caller is PTRACE_KILL, wake_up_process() is even more wrong. The tracee can sleep in any state in any place, and if we have a buggy code which doesn't handle a spurious wakeup correctly PTRACE_KILL can be used to exploit it. For example:
int main(void) { int child, status;
child = fork(); if (!child) { int ret;
assert(ptrace(PTRACE_TRACEME, 0,0,0) == 0);
ret = pause(); printf("pause: %d %m\n", ret);
return 0x23; }
sleep(1); assert(ptrace(PTRACE_KILL, child, 0,0) == 0);
assert(child == wait(&status)); printf("wait: %x\n", status);
return 0; }
prints "pause: -1 Unknown error 514", -ERESTARTNOHAND leaks to the userland. In this case sys_pause() is buggy as well and should be fixed.
I do not know what was the original rationality behind PTRACE_KILL. The man page is simply wrong and afaics it was always wrong. Imho it should be deprecated, or may be it should do send_sig(SIGKILL) as Denys suggests, but in any case I do not think that the current behaviour was intentional.
Note: there is another problem, ptrace_resume() changes ->exit_code and this can race with SIGKILL too. Eventually we should change to not use ->exit_code.
Signed-off-by: Oleg Nesterov <oleg@redhat.com> ---
kernel/ptrace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- sigprocmask/kernel/ptrace.c~ptrace_resume_wakeup 2011-05-23 18:09:48.000000000 +0200 +++ sigprocmask/kernel/ptrace.c 2011-05-23 18:20:18.000000000 +0200 @@ -561,7 +561,7 @@ static int ptrace_resume(struct task_str } child->exit_code = data; - wake_up_process(child); + wake_up_state(child, __TASK_TRACED); return 0; }
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