From: Wang Hai wanghai38@huawei.com Subject: mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook()

When I use kfree_rcu() to free a large memory allocated by kmalloc_node(), the following dump occurs.

BUG: kernel NULL pointer dereference, address: 0000000000000020 [...] Oops: 0000 [#1] SMP [...] Workqueue: events kfree_rcu_work RIP: 0010:__obj_to_index include/linux/slub_def.h:182 [inline] RIP: 0010:obj_to_index include/linux/slub_def.h:191 [inline] RIP: 0010:memcg_slab_free_hook+0x120/0x260 mm/slab.h:363 [...] Call Trace: kmem_cache_free_bulk+0x58/0x630 mm/slub.c:3293 kfree_bulk include/linux/slab.h:413 [inline] kfree_rcu_work+0x1ab/0x200 kernel/rcu/tree.c:3300 process_one_work+0x207/0x530 kernel/workqueue.c:2276 worker_thread+0x320/0x610 kernel/workqueue.c:2422 kthread+0x13d/0x160 kernel/kthread.c:313 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

When kmalloc_node() a large memory, page is allocated, not slab, so when freeing memory via kfree_rcu(), this large memory should not be used by memcg_slab_free_hook(), because memcg_slab_free_hook() is is used for slab.

Using page_objcgs_check() instead of page_objcgs() in memcg_slab_free_hook() to fix this bug.

Link: https://lkml.kernel.org/r/20210728145655.274476-1-wanghai38@huawei.com Fixes: 270c6a71460e ("mm: memcontrol/slab: Use helpers to access slab page's memcg_data") Signed-off-by: Wang Hai wanghai38@huawei.com Reviewed-by: Shakeel Butt shakeelb@google.com Acked-by: Michal Hocko mhocko@suse.com Acked-by: Roman Gushchin guro@fb.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Reviewed-by: Muchun Song songmuchun@bytedance.com Cc: Christoph Lameter cl@linux.com Cc: Pekka Enberg penberg@kernel.org Cc: David Rientjes rientjes@google.com Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Johannes Weiner hannes@cmpxchg.org Cc: Alexei Starovoitov ast@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/slab.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/slab.h~mm-memcg-fix-null-pointer-dereference-in-memcg_slab_free_hook +++ a/mm/slab.h @@ -346,7 +346,7 @@ static inline void memcg_slab_free_hook( continue;

page = virt_to_head_page(p[i]); - objcgs = page_objcgs(page); + objcgs = page_objcgs_check(page); if (!objcgs) continue;

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