Re: [PATCH 1/3] signal: In get_signal test for signal_group_exit every time through the loop

Eric W. Biederman
2021-11-17T16:31:38Z

Kees Cook <keescook@chromium.org> writes:

> On Mon, Nov 15, 2021 at 11:32:50PM -0600, Eric W. Biederman wrote:
>>
>> Recently while investigating a problem with rr and signals I noticed
>> that siglock is dropped in ptrace_signal and get_signal does not jump
>> to relock.
>>
>> Looking farther to see if the problem is anywhere else I see that
>> do_signal_stop also returns if signal_group_exit is true. I believe
>> that test can now never be true, but it is a bit hard to trace
>> through and be certain.
>>
>> Testing signal_group_exit is not expensive, so move the test for
>> signal_group_exit into the for loop inside of get_signal to ensure
>> the test is never skipped improperly.
>
> Seems reasonable.
>
>>
>> This has been a potential since I added the test for signal_group_exit
>
> nit: missing word after "potential"? "bug", "problem"?

Yes. Potential problem. I will update the comment.

>> was added.
>>
>> Fixes: 35634ffa1751 ("signal: Always notice exiting tasks")
>> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
>
> Reviewed-by: Kees Cook <keescook@chromium.org>
>
>> ---
>> kernel/signal.c | 20 ++++++++++----------
>> 1 file changed, 10 insertions(+), 10 deletions(-)
>>
>> diff --git a/kernel/signal.c b/kernel/signal.c
>> index 7c4b7ae714d4..986fa69c15c5 100644
>> --- a/kernel/signal.c
>> +++ b/kernel/signal.c
>> @@ -2662,19 +2662,19 @@ bool get_signal(struct ksignal *ksig)
>> goto relock;
>> }
>>
>> - /* Has this task already been marked for death? */
>> - if (signal_group_exit(signal)) {
>> - ksig->info.si_signo = signr = SIGKILL;
>> - sigdelset(&current->pending.signal, SIGKILL);
>> - trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,
>> - &sighand->action[SIGKILL - 1]);
>> - recalc_sigpending();
>> - goto fatal;
>> - }
>> -
>> for (;;) {
>> struct k_sigaction *ka;
>>
>> + /* Has this task already been marked for death? */
>> + if (signal_group_exit(signal)) {
>> + ksig->info.si_signo = signr = SIGKILL;
>> + sigdelset(&current->pending.signal, SIGKILL);
>> + trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,
>> + &sighand->action[SIGKILL - 1]);
>> + recalc_sigpending();
>> + goto fatal;
>> + }
>> +
>> if (unlikely(current->jobctl & JOBCTL_STOP_PENDING) &&
>> do_signal_stop(0))
>> goto relock;
>> --
>> 2.20.1
>>