kasan: drain quarantine of memcg slab objects

Per memcg slab accounting and kasan have a problem with kmem_cache
destruction.
 - kmem_cache_create() allocates a kmem_cache, which is used for
   allocations from processes running in root (top) memcg.
 - Processes running in non root memcg and allocating with either
   __GFP_ACCOUNT or from a SLAB_ACCOUNT cache use a per memcg
   kmem_cache.
 - Kasan catches use-after-free by having kfree() and kmem_cache_free()
   defer freeing of objects. Objects are placed in a quarantine.
 - kmem_cache_destroy() destroys root and non root kmem_caches. It takes
   care to drain the quarantine of objects from the root memcg's
   kmem_cache, but ignores objects associated with non root memcg. This
   causes leaks because quarantined per memcg objects refer to per memcg
   kmem cache being destroyed.

To see the problem:

 1) create a slab cache with kmem_cache_create(,,,SLAB_ACCOUNT,)
 2) from non root memcg, allocate and free a few objects from cache
 3) dispose of the cache with kmem_cache_destroy() kmem_cache_destroy()
    will trigger a "Slab cache still has objects" warning indicating
    that the per memcg kmem_cache structure was leaked.

Fix the leak by draining kasan quarantined objects allocated from non
root memcg.

Racing memcg deletion is tricky, but handled.  kmem_cache_destroy() =>
shutdown_memcg_caches() => __shutdown_memcg_cache() => shutdown_cache()
flushes per memcg quarantined objects, even if that memcg has been
rmdir'd and gone through memcg_deactivate_kmem_caches().

This leak only affects destroyed SLAB_ACCOUNT kmem caches when kasan is
enabled.  So I don't think it's worth patching stable kernels.

Link: http://lkml.kernel.org/r/1482257462-36948-1-git-send-email-gthelen@google.com
Signed-off-by: Greg Thelen <gthelen@google.com>
Reviewed-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 820c0ad54a0117596e63bae6845b1ebd771c3412..c908b25bf5a558bf7b07abb050cd5a148ed62780 100644 (file)
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -52,7 +52,7 @@ void kasan_free_pages(struct page *page, unsigned int order);
 void kasan_cache_create(struct kmem_cache *cache, size_t *size,
                        unsigned long *flags);
 void kasan_cache_shrink(struct kmem_cache *cache);
-void kasan_cache_destroy(struct kmem_cache *cache);
+void kasan_cache_shutdown(struct kmem_cache *cache);
 
 void kasan_poison_slab(struct page *page);
 void kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
@@ -98,7 +98,7 @@ static inline void kasan_cache_create(struct kmem_cache *cache,
                                      size_t *size,
                                      unsigned long *flags) {}
 static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
-static inline void kasan_cache_destroy(struct kmem_cache *cache) {}
+static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
 
 static inline void kasan_poison_slab(struct page *page) {}
 static inline void kasan_unpoison_object_data(struct kmem_cache *cache,

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index b2a0cff2bb351ae94e4115c0c3920cd2ae0fbbca..25f0e6521f36c66e349804355aac536662e11257 100644 (file)
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -435,7 +435,7 @@ void kasan_cache_shrink(struct kmem_cache *cache)
        quarantine_remove_cache(cache);
 }
 
-void kasan_cache_destroy(struct kmem_cache *cache)
+void kasan_cache_shutdown(struct kmem_cache *cache)
 {
        quarantine_remove_cache(cache);
 }

diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index dae929c02bbb991cd0f50493a431af2ea6c36c29..6f1ed16308736918730ea836b5fecafc908e487b 100644 (file)
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -274,6 +274,7 @@ static void per_cpu_remove_cache(void *arg)
        qlist_free_all(&to_free, cache);
 }
 
+/* Free all quarantined objects belonging to cache. */
 void quarantine_remove_cache(struct kmem_cache *cache)
 {
        unsigned long flags, i;

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 23ff74e618388508e359a5317d93ae284778f779..09d0e849b07f47d82f5d9a5cda4862517d297cb2 100644 (file)
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -528,6 +528,9 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
 
 static int shutdown_cache(struct kmem_cache *s)
 {
+       /* free asan quarantined objects */
+       kasan_cache_shutdown(s);
+
        if (__kmem_cache_shutdown(s) != 0)
                return -EBUSY;
 
@@ -816,7 +819,6 @@ void kmem_cache_destroy(struct kmem_cache *s)
        get_online_cpus();
        get_online_mems();
 
-       kasan_cache_destroy(s);
        mutex_lock(&slab_mutex);
 
        s->refcount--;