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@mjdsystems.ca>
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mempool.c b/mm/mempool.c
index 004d42b1dfaf928ab174e057696afa580447f3d9..7924f4f58a6d48ae5335fdedb1c2e2dd93a56d88 100644 (file)
--- 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;
 }