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>

1 files changed, 22 insertions, 1 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 474209f50844..70e76ad11fbf 100644
--- 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) !=