From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wj0-f199.google.com (mail-wj0-f199.google.com [209.85.210.199]) by kanga.kvack.org (Postfix) with ESMTP id BA2F76B03F8 for ; Thu, 22 Dec 2016 03:55:11 -0500 (EST) Received: by mail-wj0-f199.google.com with SMTP id iq1so2887832wjb.1 for ; Thu, 22 Dec 2016 00:55:11 -0800 (PST) Received: from smtp24.mail.ru (smtp24.mail.ru. [94.100.181.179]) by mx.google.com with ESMTPS id us1si30989439wjc.102.2016.12.22.00.55.09 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 22 Dec 2016 00:55:10 -0800 (PST) Date: Thu, 22 Dec 2016 11:54:58 +0300 From: Vladimir Davydov Subject: Re: [PATCH 1/2] kasan: drain quarantine of memcg slab objects Message-ID: <20161222085458.GA3494@esperanza> References: <1482257462-36948-1-git-send-email-gthelen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1482257462-36948-1-git-send-email-gthelen@google.com> Sender: owner-linux-mm@kvack.org List-ID: To: Greg Thelen Cc: Andrew Morton , Andrey Ryabinin , Alexander Potapenko , Dmitry Vyukov , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, Dec 20, 2016 at 10:11:01AM -0800, Greg Thelen wrote: > 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. > > Signed-off-by: Greg Thelen Reviewed-by: Vladimir Davydov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org