Subject: [PATCH 2/2] sched: BUG when stack end location is over written

From: Aaron Tomlin <[email-masked]>
Date: Thu, 4 Sep 2014 15:50:24 +0100

Currently in the event of a stack overrun a call to schedule()
does not check for this type of corruption. This corruption is
often silent and can go unnoticed. However once the corrupted
region is examined at a later stage, the outcome is undefined
and often results in a sporadic page fault which cannot be
handled.

This patch checks for a stack overrun and takes appropriate
action since the damage is already done, there is no point
in continuing.

Signed-off-by: Aaron Tomlin <[email-masked]>
---
 kernel/sched/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ec1a286..d6af6a0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2660,6 +2660,9 @@ static noinline void __schedule_bug(struct task_struct *prev)
  */
 static inline void schedule_debug(struct task_struct *prev)
 {
+	if (unlikely(prev != &init_task &&
+		task_stack_end_corrupted(prev)))
+		BUG();
 	/*
 	 * Test if we are atomic. Since do_exit() needs to call into
 	 * schedule() atomically, we ignore that path. Otherwise whine
-- 
1.9.3