mm, swap: consolidate bad slots setup and make it more robust

In preparation for using the swap table to track bad slots directly, move
the bad slot setup to one place, set up the swap_map mark, and cluster
counter update together.

While at it, provide more informative logs and a more robust fallback if
any bad slot info looks incorrect.

Fixes a potential issue that a malformed swap file may cause the cluster
to be unusable upon swapon, and provides a more verbose warning on a
malformed swap file

Link: https://lkml.kernel.org/r/20260218-swap-table-p3-v3-4-f4e34be021a7@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Chris Li <chrisl@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 38 insertions, 30 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 650eae8545f1..f195e90c6e8b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -743,13 +743,37 @@ static void relocate_cluster(struct swap_info_struct *si,
  * slot. The cluster will not be added to the free cluster list, and its
  * usage counter will be increased by 1. Only used for initialization.
  */
-static int swap_cluster_setup_bad_slot(struct swap_cluster_info *cluster_info,
-				       unsigned long offset)
+static int swap_cluster_setup_bad_slot(struct swap_info_struct *si,
+				       struct swap_cluster_info *cluster_info,
+				       unsigned int offset, bool mask)
 {
 	unsigned long idx = offset / SWAPFILE_CLUSTER;
 	struct swap_table *table;
 	struct swap_cluster_info *ci;
 
+	/* si->max may got shrunk by swap swap_activate() */
+	if (offset >= si->max && !mask) {
+		pr_debug("Ignoring bad slot %u (max: %u)\n", offset, si->max);
+		return 0;
+	}
+	/*
+	 * Account it, skip header slot: si->pages is initiated as
+	 * si->max - 1. Also skip the masking of last cluster,
+	 * si->pages doesn't include that part.
+	 */
+	if (offset && !mask)
+		si->pages -= 1;
+	if (!si->pages) {
+		pr_warn("Empty swap-file\n");
+		return -EINVAL;
+	}
+	/* Check for duplicated bad swap slots. */
+	if (si->swap_map[offset]) {
+		pr_warn("Duplicated bad slot offset %d\n", offset);
+		return -EINVAL;
+	}
+
+	si->swap_map[offset] = SWAP_MAP_BAD;
 	ci = cluster_info + idx;
 	if (!ci->table) {
 		table = swap_table_alloc(GFP_KERNEL);
@@ -3220,30 +3244,12 @@ static int setup_swap_map(struct swap_info_struct *si,
 			  union swap_header *swap_header,
 			  unsigned long maxpages)
 {
-	unsigned long i;
 	unsigned char *swap_map;
 
 	swap_map = vzalloc(maxpages);
 	si->swap_map = swap_map;
 	if (!swap_map)
 		return -ENOMEM;
-
-	swap_map[0] = SWAP_MAP_BAD; /* omit header page */
-	for (i = 0; i < swap_header->info.nr_badpages; i++) {
-		unsigned int page_nr = swap_header->info.badpages[i];
-		if (page_nr == 0 || page_nr > swap_header->info.last_page)
-			return -EINVAL;
-		if (page_nr < maxpages) {
-			swap_map[page_nr] = SWAP_MAP_BAD;
-			si->pages--;
-		}
-	}
-
-	if (!si->pages) {
-		pr_warn("Empty swap-file\n");
-		return -EINVAL;
-	}
-
 	return 0;
 }
 
@@ -3273,26 +3279,28 @@ static int setup_swap_clusters_info(struct swap_info_struct *si,
 	}
 
 	/*
-	 * Mark unusable pages as unavailable. The clusters aren't
-	 * marked free yet, so no list operations are involved yet.
-	 *
-	 * See setup_swap_map(): header page, bad pages,
-	 * and the EOF part of the last cluster.
+	 * Mark unusable pages (header page, bad pages, and the EOF part of
+	 * the last cluster) as unavailable. The clusters aren't marked free
+	 * yet, so no list operations are involved yet.
 	 */
-	err = swap_cluster_setup_bad_slot(cluster_info, 0);
+	err = swap_cluster_setup_bad_slot(si, cluster_info, 0, false);
 	if (err)
 		goto err;
 	for (i = 0; i < swap_header->info.nr_badpages; i++) {
 		unsigned int page_nr = swap_header->info.badpages[i];
 
-		if (page_nr >= maxpages)
-			continue;
-		err = swap_cluster_setup_bad_slot(cluster_info, page_nr);
+		if (!page_nr || page_nr > swap_header->info.last_page) {
+			pr_warn("Bad slot offset is out of border: %d (last_page: %d)\n",
+				page_nr, swap_header->info.last_page);
+			err = -EINVAL;
+			goto err;
+		}
+		err = swap_cluster_setup_bad_slot(si, cluster_info, page_nr, false);
 		if (err)
 			goto err;
 	}
 	for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++) {
-		err = swap_cluster_setup_bad_slot(cluster_info, i);
+		err = swap_cluster_setup_bad_slot(si, cluster_info, i, true);
 		if (err)
 			goto err;
 	}