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mm: slab: fix potential double free in ___cache_free

Message ID 20200926141341.785180-1-shakeelb@google.com (mailing list archive)
State New, archived
Headers show
Series mm: slab: fix potential double free in ___cache_free | expand

Commit Message

Shakeel Butt Sept. 26, 2020, 2:13 p.m. UTC
With the commit 10befea91b61 ("mm: memcg/slab: use a single set of
kmem_caches for all allocations"), it becomes possible to call kfree()
from the slabs_destroy(). The functions cache_flusharray() and
do_drain() calls slabs_destroy() on array_cache of the local CPU without
updating the size of the array_cache. This enables the kfree() call from
the slabs_destroy() to recursively call cache_flusharray() which can
potentially call free_block() on the same elements of the array_cache of
the local CPU and causing double free and memory corruption.

To fix the issue, simply update the local CPU array_cache cache before
calling slabs_destroy().

Fixes: 10befea91b61 ("mm: memcg/slab: use a single set of kmem_caches for all allocations")
Signed-off-by: Shakeel Butt <shakeelb@google.com>
Reviewed-by: Roman Gushchin <guro@fb.com>
Tested-by: Ming Lei <ming.lei@redhat.com>
Reported-by: kernel test robot <rong.a.chen@intel.com>
 mm/slab.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
diff mbox series


diff --git a/mm/slab.c b/mm/slab.c
index 3160dff6fd76..f658e86ec8ce 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1632,6 +1632,10 @@  static void slab_destroy(struct kmem_cache *cachep, struct page *page)
 		kmem_cache_free(cachep->freelist_cache, freelist);
+ * Update the size of the caches before calling slabs_destroy as it may
+ * recursively call kfree.
+ */
 static void slabs_destroy(struct kmem_cache *cachep, struct list_head *list)
 	struct page *page, *n;
@@ -2153,8 +2157,8 @@  static void do_drain(void *arg)
 	free_block(cachep, ac->entry, ac->avail, node, &list);
-	slabs_destroy(cachep, &list);
 	ac->avail = 0;
+	slabs_destroy(cachep, &list);
 static void drain_cpu_caches(struct kmem_cache *cachep)
@@ -3402,9 +3406,9 @@  static void cache_flusharray(struct kmem_cache *cachep, struct array_cache *ac)
-	slabs_destroy(cachep, &list);
 	ac->avail -= batchcount;
 	memmove(ac->entry, &(ac->entry[batchcount]), sizeof(void *)*ac->avail);
+	slabs_destroy(cachep, &list);