f2fs: fix to do sanity check in is_alive()

In fuzzed image, SSA table may indicate that a data block belongs to
invalid node, which node ID is out-of-range (0, 1, 2 or max_nid), in
order to avoid migrating inconsistent data in such corrupted image,
let's do sanity check anyway before data block migration.

Cc: stable@vger.kernel.org
Signed-off-by: NChao Yu <chao@kernel.org>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -1026,6 +1026,9 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 		set_sbi_flag(sbi, SBI_NEED_FSCK);
 	}
 
+	if (f2fs_check_nid_range(sbi, dni->ino))
+		return false;
+
 	*nofs = ofs_of_node(node_page);
 	source_blkaddr = data_blkaddr(NULL, node_page, ofs_in_node);
 	f2fs_put_page(node_page, 1);