[PATCH] mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook()

From: Wang Hai <wanghai38@huawei.com>
To: <cl@linux.com>, <penberg@kernel.org>, <rientjes@google.com>,
	<iamjoonsoo.kim@lge.com>, <akpm@linux-foundation.org>,
	<vbabka@suse.cz>, <hannes@cmpxchg.org>, <shakeelb@google.com>,
	<ast@kernel.org>, <wangkefeng.wang@huawei.com>
Cc: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: [PATCH] mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook()
Date: Wed, 28 Jul 2021 17:13:48 +0800	[thread overview]
Message-ID: <20210728091348.272714-1-wanghai38@huawei.com> (raw)

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.

So in this case, there is no need to do anything with this large
page in memcg_slab_free_hook(), just skip it.

Fixes: 270c6a71460e ("mm: memcontrol/slab: Use helpers to access slab page's memcg_data")
Signed-off-by: Wang Hai <wanghai38@huawei.com>
---
 mm/slab.h | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/mm/slab.h b/mm/slab.h
index 67e06637ff2e..247d3f9c21f7 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -339,15 +339,20 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s_orig,
 			continue;
 
 		page = virt_to_head_page(p[i]);
+		if (!s_orig) {
+			if (unlikely(!PageSlab(page))) {
+				BUG_ON(!PageCompound(page));
+				continue;
+			}
+			s = page->slab_cache;
+		} else {
+			s = s_orig;
+		}
+
 		objcgs = page_objcgs(page);
 		if (!objcgs)
 			continue;
 
-		if (!s_orig)
-			s = page->slab_cache;
-		else
-			s = s_orig;
-
 		off = obj_to_index(s, page, p[i]);
 		objcg = objcgs[off];
 		if (!objcg)
-- 
2.17.1

