btrfs: handle chunk tree lookup error in btrfs_relocate_sys_chunks()

The unhandled case in btrfs_relocate_sys_chunks() loop is a corruption,
as it could be caused only by two impossible conditions:

- at first the search key is set up to look for a chunk tree item, with
  offset -1, this is an inexact search and the key->offset will contain
  the correct offset upon a successful search, a valid chunk tree item
  cannot have an offset -1

- after first successful search, the found_key corresponds to a chunk
  item, the offset is decremented by 1 before the next loop, it's
  impossible to find a chunk item there due to alignment and size
  constraints

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 224345658ea556ac1e945743e6d8078dc5c13dad..56b0b167e3867b5c51fb00744820613076733397 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3391,7 +3391,17 @@ again:
                        mutex_unlock(&fs_info->reclaim_bgs_lock);
                        goto error;
                }
-               BUG_ON(ret == 0); /* Corruption */
+               if (ret == 0) {
+                       /*
+                        * On the first search we would find chunk tree with
+                        * offset -1, which is not possible. On subsequent
+                        * loops this would find an existing item on an invalid
+                        * offset (one less than the previous one, wrong
+                        * alignment and size).
+                        */
+                       ret = -EUCLEAN;
+                       goto error;
+               }
 
                ret = btrfs_previous_item(chunk_root, path, key.objectid,
                                          key.type);