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From: Muchun Song Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (1.0) Subject: Re: [PATCH] mm: list_lru: fix UAF for memory cgroup Date: Thu, 18 Jul 2024 19:20:14 +0800 Message-Id: References: <65b7d88b-af4f-4869-9322-e38910abce6d@suse.cz> Cc: Muchun Song , akpm@linux-foundation.org, hannes@cmpxchg.org, nphamcs@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko In-Reply-To: <65b7d88b-af4f-4869-9322-e38910abce6d@suse.cz> To: Vlastimil Babka X-Migadu-Flow: FLOW_OUT > On Jul 18, 2024, at 18:30, Vlastimil Babka wrote: >=20 > =EF=BB=BFOn 7/18/24 10:36 AM, Muchun Song wrote: >> The mem_cgroup_from_slab_obj() is supposed to be called under rcu >> lock or cgroup_mutex or others which could prevent returned memcg >> from being freed. Fix it by adding missing rcu read lock. >=20 > Was the UAF ever observed, or is this due to code review? Just code review. Thanks. > Should there be some lockdep_assert somwhere? >=20 It=E2=80=99s a good option to improve this. Maybe mem_cgroup_from_slab_obj()= is a good place. >> Fixes: 0a97c01cd20bb ("list_lru: allow explicit memcg and NUMA node selec= tion) >> Signed-off-by: Muchun Song >> --- >> mm/list_lru.c | 24 ++++++++++++++++++------ >> 1 file changed, 18 insertions(+), 6 deletions(-) >>=20 >> diff --git a/mm/list_lru.c b/mm/list_lru.c >> index 3fd64736bc458..225da0778a3be 100644 >> --- a/mm/list_lru.c >> +++ b/mm/list_lru.c >> @@ -85,6 +85,7 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, i= nt idx) >> } >> #endif /* CONFIG_MEMCG_KMEM */ >>=20 >> +/* The caller must ensure the memcg lifetime. */ >> bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid, >> struct mem_cgroup *memcg) >> { >> @@ -109,14 +110,20 @@ EXPORT_SYMBOL_GPL(list_lru_add); >>=20 >> bool list_lru_add_obj(struct list_lru *lru, struct list_head *item) >> { >> + bool ret; >> int nid =3D page_to_nid(virt_to_page(item)); >> - struct mem_cgroup *memcg =3D list_lru_memcg_aware(lru) ? >> - mem_cgroup_from_slab_obj(item) : NULL; >> + struct mem_cgroup *memcg; >>=20 >> - return list_lru_add(lru, item, nid, memcg); >> + rcu_read_lock(); >> + memcg =3D list_lru_memcg_aware(lru) ? mem_cgroup_from_slab_obj(item)= : NULL; >> + ret =3D list_lru_add(lru, item, nid, memcg); >> + rcu_read_unlock(); >> + >> + return ret; >> } >> EXPORT_SYMBOL_GPL(list_lru_add_obj); >>=20 >> +/* The caller must ensure the memcg lifetime. */ >> bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid, >> struct mem_cgroup *memcg) >> { >> @@ -139,11 +146,16 @@ EXPORT_SYMBOL_GPL(list_lru_del); >>=20 >> bool list_lru_del_obj(struct list_lru *lru, struct list_head *item) >> { >> + bool ret; >> int nid =3D page_to_nid(virt_to_page(item)); >> - struct mem_cgroup *memcg =3D list_lru_memcg_aware(lru) ? >> - mem_cgroup_from_slab_obj(item) : NULL; >> + struct mem_cgroup *memcg; >>=20 >> - return list_lru_del(lru, item, nid, memcg); >> + rcu_read_lock(); >> + memcg =3D list_lru_memcg_aware(lru) ? mem_cgroup_from_slab_obj(item)= : NULL; >> + ret =3D list_lru_del(lru, item, nid, memcg); >> + rcu_read_unlock(); >> + >> + return ret; >> } >> EXPORT_SYMBOL_GPL(list_lru_del_obj); >>=20 >=20