From 885b49b4f31fdec212e6c5e9ad0845fab266d3cf Mon Sep 17 00:00:00 2001
From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Date: Fri, 13 Oct 2017 15:58:22 -0700
Subject: kmemleak: clear stale pointers from task stacks

commit ca182551857cc2c1e6a2b7f1e72090a137a15008 upstream.

Kmemleak considers any pointers on task stacks as references.  This
patch clears newly allocated and reused vmap stacks.

Link: http://lkml.kernel.org/r/150728990124.744199.8403409836394318684.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[ Srivatsa: Backported to 4.9.y ]
Signed-off-by: Srivatsa S. Bhat <srivatsa@csail.mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/fork.c | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'kernel')

diff --git a/kernel/fork.c b/kernel/fork.c
index 70e10cb49be0..c19e6d48d57d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -184,6 +184,10 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
 			continue;
 		this_cpu_write(cached_stacks[i], NULL);
 
+#ifdef CONFIG_DEBUG_KMEMLEAK
+		/* Clear stale pointers from reused stack. */
+		memset(s->addr, 0, THREAD_SIZE);
+#endif
 		tsk->stack_vm_area = s;
 		local_irq_enable();
 		return s->addr;
-- 
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