[PATCH 5/5] btrfs-progs: tune: do not remove owner refs from tree blocks

[Siddharth Mishra]

[BUG]
On a filesystem without skinny-metadata, "btrfstune --remove-simple-quota"
can corrupt the extent items of tree blocks:

  before:
	item 31 key (30756864 EXTENT_ITEM 4096) itemoff 2363 itemsize 51
		refs 1 gen 6 flags TREE_BLOCK
		tree block key (940 INODE_ITEM 0) level 0
		(176 0x5) tree block backref root FS_TREE
  after:
	item 31 key (30756864 EXTENT_ITEM 4096) itemoff 2372 itemsize 42
		refs 1 gen 6 flags TREE_BLOCK
		tree block key (0 UNKNOWN.0 1456) level 0
		^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

and "btrfs check" then reports "backpointer mismatch" for each of them.

[CAUSE]
remove_owner_refs() takes the first inline ref right after the
btrfs_extent_item of every EXTENT_ITEM. For a tree block without
skinny-metadata that is the btrfs_tree_block_info. If the lowest byte of
its first key objectid is BTRFS_EXTENT_OWNER_REF_KEY (172, here inode
940 = 0x3ac), the tree block info is taken as an owner ref and 9 bytes of
it are removed.

The check for an extent item without inline refs is also off by one: it
reads the type byte when ptr == item_end.

[FIX]
Owner refs are only added to data extents, so skip extent items with the
TREE_BLOCK flag, and skip the item when ptr >= item_end.

Fixes: 2336a7b921ff ("btrfs-progs: btrfstune: add ability to remove squotas")
Signed-off-by: Siddharth Mishra <smish149@xxxxxxx>
---
 tune/quota.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tune/quota.c b/tune/quota.c
index a5f7fb40..187ba4f6 100644
--- a/tune/quota.c
+++ b/tune/quota.c
@@ -132,10 +132,12 @@ search_slot:
 		if (found_key.type != BTRFS_EXTENT_ITEM_KEY)
 			goto next;
 		ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);
+		if (btrfs_extent_flags(leaf, ei) & BTRFS_EXTENT_FLAG_TREE_BLOCK)
+			goto next;
 		ptr = (unsigned long)(ei + 1);
 		item_end = (unsigned long)ei + btrfs_item_size(leaf, slot);
 		/* No inline extent references; accessing type is invalid. */
-		if (ptr > item_end)
+		if (ptr >= item_end)
 			goto next;
 		iref = (struct btrfs_extent_inline_ref *)ptr;
 		type = btrfs_extent_inline_ref_type(leaf, iref);
-- 
2.54.0