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SubjectRe: [PATCH] posix-timers: Prevent broadcast signals
Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:

> From: Thomas Gleixner <tglx@linutronix.de>
>
> Posix timers should not send broadcast signals and kernel only
> signals. Prevent it.

You are not adding prevention of ``broadcast'' signals by preventing
sig_kernel_only and sig_kernel_coredump so your change description does
not make sense.

Second we are sending the signal to ourselves. It may be silly to use
a timer to send SIGKILL or SIGSTOP but I can imagine some reasons.

For signals that might coredump if you setup a handler they won't
coredump so preventing those seems even sillier.

So what is the reason for changing which signals posix timers send?

If SIGEV_THREAD_ID is specificied I can understand not wanting
to send signals that could affect more than just a thread.

if SIGEV_THREAD is specified I can understand not wanting signals
that will do more than wake up the thread. I presume glibc precreates
the thread.

Neither of those cases should apply to everything passing through
good_sigevent. So your code is wrong if those are your justification.

Further the kernel is perfectly capable of delivering all types of
signal through send_sigqueue so there is no techincal reason for
preventing these signals.

Eric


> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> kernel/time/posix-timers.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
> index b6899b5060bd..4c4cbebb0d71 100644
> --- a/kernel/time/posix-timers.c
> +++ b/kernel/time/posix-timers.c
> @@ -435,6 +435,7 @@ static enum hrtimer_restart posix_timer_fn(struct hrtimer *timer)
> static struct pid *good_sigevent(sigevent_t * event)
> {
> struct task_struct *rtn = current->group_leader;
> + int sig = event->sigev_signo;
>
> switch (event->sigev_notify) {
> case SIGEV_SIGNAL | SIGEV_THREAD_ID:
> @@ -444,7 +445,8 @@ static struct pid *good_sigevent(sigevent_t * event)
> /* FALLTHRU */
> case SIGEV_SIGNAL:
> case SIGEV_THREAD:
> - if (event->sigev_signo <= 0 || event->sigev_signo > SIGRTMAX)
> + if (sig <= 0 || sig > SIGRTMAX ||
> + sig_kernel_only(sig) || sig_kernel_coredump(sig))
> return NULL;
> /* FALLTHRU */
> case SIGEV_NONE:

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