From: Oleg Nesterov <oleg@xxxxxxxxxx>
-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
If you see a problem with using this for longterm, please comment.
-------------------
commit 0666fb51b1483f27506e212cc7f7b2645b5c7acc upstream.
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@xxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
kernel/ptrace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index b7b491e6c25b..9450ec22e5a6 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -507,7 +507,7 @@ 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;
}
--
1.8.5.2
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