Btrfs: detect corruption when non-root leaf has zero item

Right now we treat leaf which has zero item as a valid one
because we could have an empty tree, that is, a root that is
also a leaf without any item, however, in the same case but
when the leaf is not a root, we can end up with hitting the
BUG_ON(1) in btrfs_extend_item() called by
setup_inline_extent_backref().

This makes us check the situation as a corruption if leaf is
not its own root.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 474209f50844a546c2d9572a603f4dc3549e7692..70e76ad11fbf5ef2c69649dba8036b4f5f6fda70 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -560,8 +560,29 @@ static noinline int check_leaf(struct btrfs_root *root,
        u32 nritems = btrfs_header_nritems(leaf);
        int slot;
 
-       if (nritems == 0)
+       if (nritems == 0) {
+               struct btrfs_root *check_root;
+
+               key.objectid = btrfs_header_owner(leaf);
+               key.type = BTRFS_ROOT_ITEM_KEY;
+               key.offset = (u64)-1;
+
+               check_root = btrfs_get_fs_root(root->fs_info, &key, false);
+               /*
+                * The only reason we also check NULL here is that during
+                * open_ctree() some roots has not yet been set up.
+                */
+               if (!IS_ERR_OR_NULL(check_root)) {
+                       /* if leaf is the root, then it's fine */
+                       if (leaf->start !=
+                           btrfs_root_bytenr(&check_root->root_item)) {
+                               CORRUPT("non-root leaf's nritems is 0",
+                                       leaf, root, 0);
+                               return -EIO;
+                       }
+               }
                return 0;
+       }
 
        /* Check the 0 item */
        if (btrfs_item_offset_nr(leaf, 0) + btrfs_item_size_nr(leaf, 0) !=