bcachefs: Check for journal entries overruning end of sb clean section

Fix a missing bounds check in superblock validation.

Note that we don't yet have repair code for this case - repair code for
individual items is generally low priority, since the whole superblock
is checksummed, validated prior to write, and we have backups.

Reported-by: lei lu <llfamsec@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Author: Kent Overstreet

fs/bcachefs/sb-clean.c

@@ -29,6 +29,14 @@ int bch2_sb_clean_validate_late(struct bch_fs *c, struct bch_sb_field_clean *cle
 	for (entry = clean->start;
 	     entry < (struct jset_entry *) vstruct_end(&clean->field);
 	     entry = vstruct_next(entry)) {
+		if (vstruct_end(entry) > vstruct_end(&clean->field)) {
+			bch_err(c, "journal entry (u64s %u) overran end of superblock clean section (u64s %u) by %zu",
+				le16_to_cpu(entry->u64s), le32_to_cpu(clean->field.u64s),
+				(u64 *) vstruct_end(entry) - (u64 *) vstruct_end(&clean->field));
+			bch2_sb_error_count(c, BCH_FSCK_ERR_sb_clean_entry_overrun);
+			return -BCH_ERR_fsck_repair_unimplemented;
+		}
+
 		ret = bch2_journal_entry_validate(c, NULL, entry,
 						  le16_to_cpu(c->disk_sb.sb->version),
 						  BCH_SB_BIG_ENDIAN(c->disk_sb.sb),

fs/bcachefs/sb-errors_types.h

@@ -271,7 +271,8 @@
 	x(btree_root_unreadable_and_scan_found_nothing,		263)	\
 	x(snapshot_node_missing,				264)	\
 	x(dup_backpointer_to_bad_csum_extent,			265)	\
-	x(btree_bitmap_not_marked,				266)
+	x(btree_bitmap_not_marked,				266)	\
+	x(sb_clean_entry_overrun,				267)
 
 enum bch_sb_error_id {
 #define x(t, n) BCH_FSCK_ERR_##t = n,