Re: [PATCH] mm: list_lru: fix UAF for memory cgroup

[Muchun Song <muchun.song@linux.dev>]

> On Jul 18, 2024, at 19:20, Muchun Song <muchun.song@linux.dev> wrote:
> 
> 
> 
>> On Jul 18, 2024, at 18:30, Vlastimil Babka <vbabka@suse.cz> wrote:
>> 
>> On 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.
>> 
>> Was the UAF ever observed, or is this due to code review?
> 
> Just code review.
> 
> Thanks.
> 
>> Should there be some lockdep_assert somwhere?
>> 
> 
> It’s a good option to improve this. Maybe mem_cgroup_from_slab_obj() is a good place.

I added it to obj_cgroup_memcg() [1]. And CC memory cgroup maintainers to this thread.


[1] https://lore.kernel.org/linux-mm/20859F67-A80C-4FD0-990C-40C70905E55B@linux.dev/T/

> 
>>> Fixes: 0a97c01cd20bb ("list_lru: allow explicit memcg and NUMA node selection)
>>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>>> ---
>>> mm/list_lru.c | 24 ++++++++++++++++++------
>>> 1 file changed, 18 insertions(+), 6 deletions(-)
>>> 
>>> 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, int idx)
>>> }
>>> #endif /* CONFIG_MEMCG_KMEM */
>>> 
>>> +/* 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);
>>> 
>>> 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();
>>> +
>>> +    return ret;
>>> }
>>> EXPORT_SYMBOL_GPL(list_lru_add_obj);
>>> 
>>> +/* 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);
>>> 
>>> bool list_lru_del_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_del(lru, item, nid, memcg);
>>> +    rcu_read_lock();
>>> +    memcg = list_lru_memcg_aware(lru) ? mem_cgroup_from_slab_obj(item) : NULL;
>>> +    ret = list_lru_del(lru, item, nid, memcg);
>>> +    rcu_read_unlock();
>>> +
>>> +    return ret;
>>> }
>>> EXPORT_SYMBOL_GPL(list_lru_del_obj);
>>> 
>>