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 --- mm/slab_common.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'mm/slab_common.c') diff --git a/mm/slab_common.c b/mm/slab_common.c index 23ff74e61838..09d0e849b07f 100644 --- 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--; -- cgit v1.2.3