mm/mempool: allow NULL `pool' pointer in mempool_destroy()

mempool_destroy() does not tolerate a NULL mempool_t pointer argument and
performs a NULL-pointer dereference.  This requires additional attention
and effort from developers/reviewers and forces all mempool_destroy()
callers to do a NULL check

    if (pool)
        mempool_destroy(pool);

Or, otherwise, be invalid mempool_destroy() users.

Tweak mempool_destroy() and NULL-check the pointer there.

Proposed by Andrew Morton.

Link: https://lkml.org/lkml/2015/6/8/583
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/mm/mempool.c b/mm/mempool.c
index 2cc08de8b1db..4c533bc51d73 100644
--- a/mm/mempool.c
+++ b/mm/mempool.c
@@ -150,6 +150,9 @@ static void *remove_element(mempool_t *pool)
  */
 void mempool_destroy(mempool_t *pool)
 {
+        if (unlikely(!pool))
+                return;
+
         while (pool->curr_nr) {
                 void *element = remove_element(pool);
                 pool->free(element, pool->pool_data);