From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f175.google.com (mail-lb0-f175.google.com [209.85.217.175]) by kanga.kvack.org (Postfix) with ESMTP id 5967C6B003B for ; Mon, 6 Jan 2014 03:45:35 -0500 (EST) Received: by mail-lb0-f175.google.com with SMTP id w6so9655076lbh.34 for ; Mon, 06 Jan 2014 00:45:34 -0800 (PST) Received: from relay.parallels.com (relay.parallels.com. [195.214.232.42]) by mx.google.com with ESMTPS id rc10si35757242lbb.89.2014.01.06.00.45.34 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Mon, 06 Jan 2014 00:45:34 -0800 (PST) From: Vladimir Davydov Subject: [PATCH RESEND 05/11] memcg: fix possible NULL deref while traversing memcg_slab_caches list Date: Mon, 6 Jan 2014 12:44:56 +0400 Message-ID: In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: mhocko@suse.cz, akpm@linux-foundation.org Cc: glommer@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, devel@openvz.org, Johannes Weiner , Balbir Singh , KAMEZAWA Hiroyuki All caches of the same memory cgroup are linked in the memcg_slab_caches list via kmem_cache::memcg_params::list. This list is traversed, for example, when we read memory.kmem.slabinfo. Since the list actually consists of memcg_cache_params objects, we have to convert an element of the list to a kmem_cache object using memcg_params_to_cache(), which obtains the pointer to the cache from the memcg_params::memcg_caches array of the corresponding root cache. That said the pointer to a kmem_cache in its parent's memcg_params must be initialized before adding the cache to the list, and cleared only after it has been unlinked. Currently it is vice-versa, which can result in a NULL ptr dereference while traversing the memcg_slab_caches list. This patch restores the correct order. Signed-off-by: Vladimir Davydov Cc: Michal Hocko Cc: Glauber Costa Cc: Johannes Weiner Cc: Balbir Singh Cc: KAMEZAWA Hiroyuki Cc: Andrew Morton --- mm/memcontrol.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 999e7d4..d918626 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3234,9 +3234,6 @@ void memcg_register_cache(struct kmem_cache *s) css_get(&memcg->css); - mutex_lock(&memcg->slab_caches_mutex); - list_add(&s->memcg_params->list, &memcg->memcg_slab_caches); - mutex_unlock(&memcg->slab_caches_mutex); /* * Since readers won't lock (see cache_from_memcg_idx()), we need a @@ -3245,7 +3242,16 @@ void memcg_register_cache(struct kmem_cache *s) */ smp_wmb(); + /* + * Initialize the pointer to this cache in its parent's memcg_params + * before adding it to the memcg_slab_caches list, otherwise we can + * fail to convert memcg_params_to_cache() while traversing the list. + */ root->memcg_params->memcg_caches[id] = s; + + mutex_lock(&memcg->slab_caches_mutex); + list_add(&s->memcg_params->list, &memcg->memcg_slab_caches); + mutex_unlock(&memcg->slab_caches_mutex); } void memcg_unregister_cache(struct kmem_cache *s) @@ -3257,16 +3263,21 @@ void memcg_unregister_cache(struct kmem_cache *s) if (is_root_cache(s)) return; - memcg = s->memcg_params->memcg; - id = memcg_cache_id(memcg); - root = s->memcg_params->root_cache; - root->memcg_params->memcg_caches[id] = NULL; + memcg = s->memcg_params->memcg; + id = memcg_cache_id(memcg); mutex_lock(&memcg->slab_caches_mutex); list_del(&s->memcg_params->list); mutex_unlock(&memcg->slab_caches_mutex); + /* + * Clear the pointer to this cache in its parent's memcg_params only + * after removing it from the memcg_slab_caches list, otherwise we can + * fail to convert memcg_params_to_cache() while traversing the list. + */ + root->memcg_params->memcg_caches[id] = NULL; + css_put(&memcg->css); } -- 1.7.10.4 -- 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