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authorVladimir Davydov <vdavydov@parallels.com>2014-12-12 16:56:38 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-12-13 12:42:49 -0800
commit8135be5a8012f4c7e95218563855e16c09a8271b (patch)
tree49e85409f82f5973a0cbf21e3e3eac382daa515b /mm/slab.c
parentae6e71d3d900c398bdb346ac25733b2efa9b3752 (diff)
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memcg: fix possible use-after-free in memcg_kmem_get_cache()
Suppose task @t that belongs to a memory cgroup @memcg is going to allocate an object from a kmem cache @c. The copy of @c corresponding to @memcg, @mc, is empty. Then if kmem_cache_alloc races with the memory cgroup destruction we can access the memory cgroup's copy of the cache after it was destroyed: CPU0 CPU1 ---- ---- [ current=@t @mc->memcg_params->nr_pages=0 ] kmem_cache_alloc(@c): call memcg_kmem_get_cache(@c); proceed to allocation from @mc: alloc a page for @mc: ... move @t from @memcg destroy @memcg: mem_cgroup_css_offline(@memcg): memcg_unregister_all_caches(@memcg): kmem_cache_destroy(@mc) add page to @mc We could fix this issue by taking a reference to a per-memcg cache, but that would require adding a per-cpu reference counter to per-memcg caches, which would look cumbersome. Instead, let's take a reference to a memory cgroup, which already has a per-cpu reference counter, in the beginning of kmem_cache_alloc to be dropped in the end, and move per memcg caches destruction from css offline to css free. As a side effect, per-memcg caches will be destroyed not one by one, but all at once when the last page accounted to the memory cgroup is freed. This doesn't sound as a high price for code readability though. Note, this patch does add some overhead to the kmem_cache_alloc hot path, but it is pretty negligible - it's just a function call plus a per cpu counter decrement, which is comparable to what we already have in memcg_kmem_get_cache. Besides, it's only relevant if there are memory cgroups with kmem accounting enabled. I don't think we can find a way to handle this race w/o it, because alloc_page called from kmem_cache_alloc may sleep so we can't flush all pending kmallocs w/o reference counting. Signed-off-by: Vladimir Davydov <vdavydov@parallels.com> Acked-by: Christoph Lameter <cl@linux.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.cz> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/slab.c')
-rw-r--r--mm/slab.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/mm/slab.c b/mm/slab.c
index fee275b5b6b7..6042fe57cc60 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3182,6 +3182,7 @@ slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
memset(ptr, 0, cachep->object_size);
}
+ memcg_kmem_put_cache(cachep);
return ptr;
}
@@ -3247,6 +3248,7 @@ slab_alloc(struct kmem_cache *cachep, gfp_t flags, unsigned long caller)
memset(objp, 0, cachep->object_size);
}
+ memcg_kmem_put_cache(cachep);
return objp;
}