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Message-Id: <62BBC2A6-D6C3-48B8-B049-932E3BC16F31@linux.dev>
Date: Wed, 24 Jul 2024 10:23:43 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Muchun Song <songmuchun@...edance.com>,
Johannes Weiner <hannes@...xchg.org>,
Nhat Pham <nphamcs@...il.com>,
Linux Memory Management List <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: list_lru: fix UAF for memory cgroup
> On Jul 24, 2024, at 08:45, Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Thu, 18 Jul 2024 16:36:07 +0800 Muchun Song <songmuchun@...edance.com> 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.
>
> "or others" is rather vague. What others?
Like objcg_lock. I have added this one into obj_cgroup_memcg().
>
>> @@ -109,14 +110,20 @@ EXPORT_SYMBOL_GPL(list_lru_add);
>>
>> bool list_lru_add_obj(struct list_lru *lru, struct list_head *item)
>> {
>> + bool ret;
>> int nid = page_to_nid(virt_to_page(item));
>> - struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ?
>> - mem_cgroup_from_slab_obj(item) : NULL;
>> + struct mem_cgroup *memcg;
>>
>> - return list_lru_add(lru, item, nid, memcg);
>> + rcu_read_lock();
>> + memcg = list_lru_memcg_aware(lru) ? mem_cgroup_from_slab_obj(item) : NULL;
>> + ret = list_lru_add(lru, item, nid, memcg);
>> + rcu_read_unlock();
>
> We don't need rcu_read_lock() to evaluate NULL.
>
> memcg = NULL;
> if (list_lru_memcg_aware(lru)) {
> rcu_read_lock();
> memcg = mem_cgroup_from_slab_obj(item);
> rcu_read_unlock();
Actually, the access to memcg is in list_lru_add(), so the rcu lock should
also cover this function rather than only mem_cgroup_from_slab_obj().
Something like:
memcg = NULL;
if (list_lru_memcg_aware(lru)) {
rcu_read_lock();
memcg = mem_cgroup_from_slab_obj(item);
}
ret = list_lru_add(lru, item, nid, memcg);
if (list_lru_memcg_aware(lru))
rcu_read_unlock();
Not concise. I don't know if this is good.
> }
>
> Seems worthwhile?
>
>
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