linux-kernel - [PATCH] ksm: Fix potential NULL pointer dereference

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Message-ID: <20250925031358.80983-1-wangfushuai@baidu.com>
Date: Thu, 25 Sep 2025 11:13:58 +0800
From: Fushuai Wang <wangfushuai@...du.com>
To: <akpm@...ux-foundation.org>, <david@...hat.com>, <xu.xin16@....com.cn>,
	<chengming.zhou@...ux.dev>
CC: <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<cuigaosheng1@...wei.com>, Fushuai Wang <wangfushuai@...du.com>
Subject: [PATCH] ksm: Fix potential NULL pointer dereference

The stable_tree_search() function may return an error pointer
(NULL or ERR_PTR(...)). The current code does not check for
these cases before dereferencing the returned value.

Gaosheng once added the necessary check in commit 98c3ca0015b8
("ksm: convert cmp_and_merge_page() to use a folio"), but it seems
the check was lost during the process of being merged into the
mainline.

Fixes: 98c3ca0015b8 ("ksm: convert cmp_and_merge_page() to use a folio")
Signed-off-by: Fushuai Wang <wangfushuai@...du.com>
---
 mm/ksm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 160787bb121c..7aa9b2829a7b 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2272,7 +2272,8 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
 
 	/* Start by searching for the folio in the stable tree */
 	kfolio = stable_tree_search(page);
-	if (&kfolio->page == page && rmap_item->head == stable_node) {
+	if (!IS_ERR_OR_NULL(kfolio) && &kfolio->page == page &&
+	    rmap_item->head == stable_node) {
 		folio_put(kfolio);
 		return;
 	}
-- 
2.36.1