linux-kernel - [PATCH] mm: list_lru: Fix NULL pointer dereference in list_lru

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Message-Id: <20240712032554.444823-1-youling.tang@linux.dev>
Date: Fri, 12 Jul 2024 11:25:54 +0800
From: Youling Tang <youling.tang@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Youling Tang <tangyouling@...inos.cn>
Subject: [PATCH] mm: list_lru: Fix NULL pointer dereference in list_lru_add()

From: Youling Tang <tangyouling@...inos.cn>

Note that list_lru_from_memcg_idx() may return NULL, so it is necessary
to error handle the return value to avoid triggering NULL pointer
dereference BUG.

The issue was triggered for discussion [1],
Link [1]: https://lore.kernel.org/linux-bcachefs/84de6cb1-57bd-42f7-8029-4203820ef0b4@linux.dev/T/#m901bb26cdb1d9d4bacebf0d034f0a5a712cc93a6

Signed-off-by: Youling Tang <tangyouling@...inos.cn>
---
 mm/list_lru.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 3fd64736bc45..ee7424c3879d 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -94,6 +94,9 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
 	spin_lock(&nlru->lock);
 	if (list_empty(item)) {
 		l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
+		if (!l)
+			goto out;
+
 		list_add_tail(item, &l->list);
 		/* Set shrinker bit if the first element was added */
 		if (!l->nr_items++)
@@ -102,6 +105,7 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
 		spin_unlock(&nlru->lock);
 		return true;
 	}
+out:
 	spin_unlock(&nlru->lock);
 	return false;
 }
-- 
2.34.1