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Date: Sat, 21 Dec 2013 19:53:56 +0400 From: Vladimir Davydov <vdavydov@...allels.com> To: <mhocko@...e.cz> CC: <glommer@...il.com>, <akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, <cgroups@...r.kernel.org>, <devel@...nvz.org>, Johannes Weiner <hannes@...xchg.org>, Balbir Singh <bsingharora@...il.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Subject: [PATCH 05/11] memcg: fix possible NULL deref while traversing memcg_slab_caches list 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 <vdavydov@...allels.com> Cc: Michal Hocko <mhocko@...e.cz> Cc: Glauber Costa <glommer@...il.com> Cc: Johannes Weiner <hannes@...xchg.org> Cc: Balbir Singh <bsingharora@...il.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Cc: Andrew Morton <akpm@...ux-foundation.org> --- 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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