Re: [PATCH v2] mm: list_lru: fix UAF for memory cgroup

[Vlastimil Babka <vbabka@suse.cz>]

On 8/1/24 04:46, 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.
> 
> Fixes: 0a97c01cd20b ("list_lru: allow explicit memcg and NUMA node selection")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> Cc: <stable@vger.kernel.org>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> v2:
>  Only grab rcu lock when necessary (Vlastimil Babka)
> 
>  mm/list_lru.c | 28 ++++++++++++++++++++++------
>  1 file changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index a29d96929d7c7..9b7ff06e9d326 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 */
>  
> +/* 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 +110,22 @@ 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;
>  
> -	return list_lru_add(lru, item, nid, memcg);
> +	if (list_lru_memcg_aware(lru)) {
> +		rcu_read_lock();
> +		ret = list_lru_add(lru, item, nid, mem_cgroup_from_slab_obj(item));
> +		rcu_read_unlock();
> +	} else {
> +		ret = list_lru_add(lru, item, nid, NULL);
> +	}
> +
> +	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 +148,18 @@ 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;
>  
> -	return list_lru_del(lru, item, nid, memcg);
> +	if (list_lru_memcg_aware(lru)) {
> +		rcu_read_lock();
> +		ret = list_lru_del(lru, item, nid, mem_cgroup_from_slab_obj(item));
> +		rcu_read_unlock();
> +	} else {
> +		ret = list_lru_del(lru, item, nid, NULL);
> +	}
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL_GPL(list_lru_del_obj);
>