mm: slab: fix potential double free in ___cache_free

With the commit faa69fb579fc ("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: faa69fb579fc ("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>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ted Ts'o <tytso@mit.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/slab.c b/mm/slab.c
index 3160dff6fd76729d2573e8a3680fd12fcaba10d0..f658e86ec8ceeee6567829d48345c7fa9260a237 100644 (file)
--- 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);
 }
 
 /*