Commit 834d216e authored Aug 22, 2007 by Oleg Nesterov Committed by Linus Torvalds Aug 22, 2007

signalfd: fix interaction with posix-timers



dequeue_signal:

	if (__SI_TIMER) {
		spin_unlock(&tsk->sighand->siglock);
		do_schedule_next_timer(info);
		spin_lock(&tsk->sighand->siglock);
	}

Unless tsk == curent, this is absolutely unsafe: nothing prevents tsk from
exiting. If signalfd was passed to another process, do_schedule_next_timer()
is just wrong.

Add yet another "tsk == current" check into dequeue_signal().

This patch fixes an oopsable bug, but breaks the scheduling of posix timers
if the shared __SI_TIMER signal was fetched via signalfd attached to another
sub-thread. Mostly fixed by the next patch.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Roland McGrath <roland@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent d02479bd

kernel/signal.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -378,7 +378,7 @@ int dequeue_signal(struct task_struct tsk, sigset_t mask, siginfo_t *info)
		/* We only dequeue private signals from ourselves, we don't let
		* signalfd steal them
		*/
		if (tsk == current)
		if (likely(tsk == current))
		signr = __dequeue_signal(&tsk->pending, mask, info);
		if (!signr) {
		signr = __dequeue_signal(&tsk->signal->shared_pending,
		@@ -425,7 +425,7 @@ int dequeue_signal(struct task_struct tsk, sigset_t mask, siginfo_t *info)
		if (!(tsk->signal->flags & SIGNAL_GROUP_EXIT))
		tsk->signal->flags \|= SIGNAL_STOP_DEQUEUED;
		}
		if ( signr &&
		if (signr && likely(tsk == current) &&
		((info->si_code & __SI_MASK) == __SI_TIMER) &&
		info->si_sys_private){
		/*

Admin message