[Devel] [PATCH RHEL7 COMMIT] mm/mempool: avoid KASAN marking mempool poison checks as use-after-free

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.1.1.vz7.37.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.1.1.vz7.37.4
------>
commit 3a378120ff664e80662d0b2ab0c4bf468739cc0c
Author: Matthew Dawson <matthew at mjdsystems.ca>
Date:   Fri Sep 15 17:14:47 2017 +0300

    mm/mempool: avoid KASAN marking mempool poison checks as use-after-free
    
    When removing an element from the mempool, mark it as unpoisoned in KASAN
    before verifying its contents for SLUB/SLAB debugging.  Otherwise KASAN
    will flag the reads checking the element use-after-free writes as
    use-after-free reads.
    
    Signed-off-by: Matthew Dawson <matthew at mjdsystems.ca>
    Acked-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    https://jira.sw.ru/browse/PSBM-69081
    (cherry picked from commit 7640131032db9118a78af715ac77ba2debeeb17c)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/mempool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mempool.c b/mm/mempool.c
index d9fa60d..791ec8a 100644
--- a/mm/mempool.c
+++ b/mm/mempool.c
@@ -135,8 +135,8 @@ static void *remove_element(mempool_t *pool)
 	void *element = pool->elements[--pool->curr_nr];
 
 	BUG_ON(pool->curr_nr < 0);
-	check_element(pool, element);
 	kasan_unpoison_element(pool, element);
+	check_element(pool, element);
 	return element;
 }