f2fs: validate orphan inode entry count

f2fs_recover_orphan_inodes() trusts the orphan block entry_count when
replaying orphan inodes from the checkpoint pack. A corrupted entry_count
larger than F2FS_ORPHANS_PER_BLOCK makes the recovery loop read past the
ino[] array and interpret footer or following data as inode numbers.

On a crafted image, mounting an unpatched kernel can drive orphan recovery
into f2fs_bug_on() and panic the kernel. Validate entry_count before
consuming entries so corrupted checkpoint data fails the mount with
-EFSCORRUPTED and requests fsck instead.

Set ERROR_INCONSISTENT_ORPHAN as well, so the corruption reason can be
recorded in the superblock s_errors[] field. This gives fsck a persistent
hint even though mount-time orphan recovery failure may leave no chance to
persist SBI_NEED_FSCK through a checkpoint.

Cc: stable@kernel.org
Fixes: 127e670abf ("f2fs: add checkpoint operations")
Signed-off-by: Wenjie Qi <qiwenjie@xiaomi.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/checkpoint.c

@@ -943,6 +943,7 @@ int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi)
 	for (i = 0; i < orphan_blocks; i++) {
 		struct folio *folio;
 		struct f2fs_orphan_block *orphan_blk;
+		unsigned int entry_count;
 
 		folio = f2fs_get_meta_folio(sbi, start_blk + i);
 		if (IS_ERR(folio)) {
@@ -951,7 +952,18 @@ int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi)
 		}
 
 		orphan_blk = folio_address(folio);
-		for (j = 0; j < le32_to_cpu(orphan_blk->entry_count); j++) {
+		entry_count = le32_to_cpu(orphan_blk->entry_count);
+		if (entry_count > F2FS_ORPHANS_PER_BLOCK) {
+			f2fs_err(sbi, "invalid orphan inode entry count %u",
+				 entry_count);
+			set_sbi_flag(sbi, SBI_NEED_FSCK);
+			f2fs_handle_error(sbi, ERROR_INCONSISTENT_ORPHAN);
+			err = -EFSCORRUPTED;
+			f2fs_folio_put(folio, true);
+			goto out;
+		}
+
+		for (j = 0; j < entry_count; j++) {
 			nid_t ino = le32_to_cpu(orphan_blk->ino[j]);
 
 			err = recover_orphan_inode(sbi, ino);

include/linux/f2fs_fs.h

@@ -107,6 +107,7 @@ enum f2fs_error {
 	ERROR_CORRUPTED_XATTR,
 	ERROR_INVALID_NODE_REFERENCE,
 	ERROR_INCONSISTENT_NAT,
+	ERROR_INCONSISTENT_ORPHAN,
 	ERROR_MAX,
 };