linux-kernel - [PATCH 3/4] mm: swap: fix potensial buffer overflow in setup

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Message-Id: <20250522122554.12209-4-shikemeng@huaweicloud.com>
Date: Thu, 22 May 2025 20:25:53 +0800
From: Kemeng Shi <shikemeng@...weicloud.com>
To: akpm@...ux-foundation.org
Cc: kasong@...cent.com,
	bhe@...hat.com,
	hannes@...xchg.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/4] mm: swap: fix potensial buffer overflow in setup_clusters()

In setup_swap_map(), we only ensure badpages are in range (0, last_page].
As maxpages might be < last_page, setup_clusters() will encounter a
buffer overflow when a badpage is >= maxpages.
Only call inc_cluster_info_page() for badpage which is < maxpages to
fix the issue.

Fixes: b843786b0bd01 ("mm: swapfile: fix SSD detection with swapfile on btrfs")
Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
---
 mm/swapfile.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index a82f4ebefca3..63ab9f14b2c6 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3208,9 +3208,13 @@ static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
 	 * and the EOF part of the last cluster.
 	 */
 	inc_cluster_info_page(si, cluster_info, 0);
-	for (i = 0; i < swap_header->info.nr_badpages; i++)
-		inc_cluster_info_page(si, cluster_info,
-				      swap_header->info.badpages[i]);
+	for (i = 0; i < swap_header->info.nr_badpages; i++) {
+		unsigned int page_nr = swap_header->info.badpages[i];
+
+		if (page_nr >= maxpages)
+			continue;
+		inc_cluster_info_page(si, cluster_info, page_nr);
+	}
 	for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++)
 		inc_cluster_info_page(si, cluster_info, i);
 
-- 
2.30.0