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author | Oleg Nesterov <oleg@redhat.com> | 2011-05-25 19:20:21 +0200 |
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committer | Oleg Nesterov <oleg@redhat.com> | 2011-05-25 19:20:21 +0200 |
commit | 0666fb51b1483f27506e212cc7f7b2645b5c7acc (patch) | |
tree | ceb625d70f0c730a46e2d954b74d687cc36b0030 | |
parent | 22e12bbc9bc38c6d0bd541d061a0f547596fc19d (diff) | |
download | linux-0666fb51b1483f27506e212cc7f7b2645b5c7acc.tar.gz linux-0666fb51b1483f27506e212cc7f7b2645b5c7acc.tar.bz2 linux-0666fb51b1483f27506e212cc7f7b2645b5c7acc.zip |
ptrace: ptrace_resume() shouldn't wake up !TASK_TRACED thread
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 ptrace
to not use ->exit_code.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
-rw-r--r-- | kernel/ptrace.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 7a81fc071344..2df115790cd9 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -562,7 +562,7 @@ static int ptrace_resume(struct task_struct *child, long request, } child->exit_code = data; - wake_up_process(child); + wake_up_state(child, __TASK_TRACED); return 0; } |