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Commit 96403da2 authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds
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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: default avatarVladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 959c8963
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