From f9fa1d919c696e90c887d8742198023e7639d139 Mon Sep 17 00:00:00 2001 From: Greg Thelen Date: Fri, 24 Feb 2017 15:00:05 -0800 Subject: 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 Reviewed-by: Vladimir Davydov Acked-by: Andrey Ryabinin Cc: Alexander Potapenko Cc: Dmitry Vyukov Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/kasan.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/kasan.h b/include/linux/kasan.h index 820c0ad54a01..c908b25bf5a5 100644 --- 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, -- cgit v1.2.3