mm: swap: fix potential buffer overflow in setup_clusters()

JIRA: https://issues.redhat.com/browse/RHEL-114865
CVE: CVE-2025-39727

commit 152c133
Author: Kemeng Shi <shikemeng@huaweicloud.com>
Date:   Thu May 22 20:25:53 2025 +0800

    mm: swap: fix potential 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.

    Link: https://lkml.kernel.org/r/20250522122554.12209-4-shikemeng@huaweicloud.com
    Fixes: b843786 ("mm: swapfile: fix SSD detection with swapfile on btrfs")
    Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
    Reviewed-by: Baoquan He <bhe@redhat.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Kairui Song <kasong@tencent.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

mm/swapfile.c

@@ -3322,9 +3322,13 @@ 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);