From 678ff6a7afccc43d352c1b8c94b6d8c0ee1464ad Mon Sep 17 00:00:00 2001 From: Shakeel Butt Date: Sat, 26 Sep 2020 07:13:41 -0700 Subject: [PATCH] mm: slab: fix potential double free in ___cache_free 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 Reviewed-by: Roman Gushchin Tested-by: Ming Lei Reported-by: kernel test robot Cc: Andrew Morton Cc: Ted Ts'o Signed-off-by: Linus Torvalds --- mm/slab.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) 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) spin_lock(&n->list_lock); free_block(cachep, ac->entry, ac->avail, node, &list); spin_unlock(&n->list_lock); - slabs_destroy(cachep, &list); ac->avail = 0; + slabs_destroy(cachep, &list); } static void drain_cpu_caches(struct kmem_cache *cachep) @@ -3402,9 +3406,9 @@ free_done: } #endif spin_unlock(&n->list_lock); - slabs_destroy(cachep, &list); ac->avail -= batchcount; memmove(ac->entry, &(ac->entry[batchcount]), sizeof(void *)*ac->avail); + slabs_destroy(cachep, &list); } /*