| Date | Tue, 04 Jun 2013 19:21:48 +0200 | From | Willy Tarreau <> | Subject | [ 018/184] ptrace: ptrace_resume() shouldnt wake up |
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2.6.32-longterm review patch. If anyone has any objections, please let me know.
------------------ !TASK_TRACED thread
From: Oleg Nesterov <oleg@redhat.com>
ptrace: ptrace_resume() shouldn't wake up !TASK_TRACED thread
CVE-2013-0871
BugLink: http://bugs.launchpad.net/bugs/1129192
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> (cherry picked from commit 0666fb51b1483f27506e212cc7f7b2645b5c7acc)
Signed-off-by: Luis Henriques <luis.henriques@canonical.com> Acked-by: Colin King <colin.king@canonical.com> Signed-off-by: Tim Gardner <tim.gardner@canonical.com> Signed-off-by: Willy Tarreau <w@1wt.eu> --- kernel/ptrace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 05625f6..d8184b5 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -506,7 +506,7 @@ static int ptrace_resume(struct task_struct *child, long request, long data) } child->exit_code = data; - wake_up_process(child); + wake_up_state(child, __TASK_TRACED); return 0; } -- 1.7.12.2.21.g234cd45.dirty
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