UPSTREAM: posix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del()
commit f90fff1e152dedf52b932240ebbd670d83330eca upstream.
If an exiting non-autoreaping task has already passed exit_notify() and
calls handle_posix_cpu_timers() from IRQ, it can be reaped by its parent
or debugger right after unlock_task_sighand().
If a concurrent posix_cpu_timer_del() runs at that moment, it won't be
able to detect timer->it.cpu.firing != 0: cpu_timer_task_rcu() and/or
lock_task_sighand() will fail.
Add the tsk->exit_state check into run_posix_cpu_timers() to fix this.
This fix is not needed if CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y, because
exit_task_work() is called before exit_notify(). But the check still
makes sense, task_work_add(&tsk->posix_cputimers_work.work) will fail
anyway in this case.
Bug: 425282960
Cc: stable@vger.kernel.org
Reported-by: Benoît Sevens <bsevens@google.com>
Fixes: 0bdd2ed4138e ("sched: run_posix_cpu_timers: Don't check ->exit_state, use lock_task_sighand()")
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit c29d5318708e67ac13c1b6fc1007d179fb65b4d7)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I2a9b8114abf2647c346e763edee1d424a07e86fe
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 6b62713..995e632 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1432,6 +1432,15 @@ void run_posix_cpu_timers(void)
lockdep_assert_irqs_disabled();
/*
+ * Ensure that release_task(tsk) can't happen while
+ * handle_posix_cpu_timers() is running. Otherwise, a concurrent
+ * posix_cpu_timer_del() may fail to lock_task_sighand(tsk) and
+ * miss timer->it.cpu.firing != 0.
+ */
+ if (tsk->exit_state)
+ return;
+
+ /*
* If the actual expiry is deferred to task work context and the
* work is already scheduled there is no point to do anything here.
*/
