[PATCH 4.2 27/54] btrfs: fix use after free iterating extrefs

[Greg Kroah-Hartman]

4.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chris Mason <clm@xxxxxx>

commit dc6c5fb3b514221f2e9d21ee626a9d95d3418dff upstream.

The code for btrfs inode-resolve has never worked properly for
files with enough hard links to trigger extrefs.  It was trying to
get the leaf out of a path after freeing the path:

	btrfs_release_path(path);
	leaf = path->nodes[0];
	item_size = btrfs_item_size_nr(leaf, slot);

The fix here is to use the extent buffer we cloned just a little higher
up to avoid deadlocks caused by using the leaf in the path.

Signed-off-by: Chris Mason <clm@xxxxxx>
cc: Mark Fasheh <mfasheh@xxxxxxx>
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Reviewed-by: Mark Fasheh <mfasheh@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/btrfs/backref.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -1809,7 +1809,6 @@ static int iterate_inode_extrefs(u64 inu
 	int found = 0;
 	struct extent_buffer *eb;
 	struct btrfs_inode_extref *extref;
-	struct extent_buffer *leaf;
 	u32 item_size;
 	u32 cur_offset;
 	unsigned long ptr;
@@ -1837,9 +1836,8 @@ static int iterate_inode_extrefs(u64 inu
 		btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
 		btrfs_release_path(path);
 
-		leaf = path->nodes[0];
-		item_size = btrfs_item_size_nr(leaf, slot);
-		ptr = btrfs_item_ptr_offset(leaf, slot);
+		item_size = btrfs_item_size_nr(eb, slot);
+		ptr = btrfs_item_ptr_offset(eb, slot);
 		cur_offset = 0;
 
 		while (cur_offset < item_size) {
@@ -1853,7 +1851,7 @@ static int iterate_inode_extrefs(u64 inu
 			if (ret)
 				break;
 
-			cur_offset += btrfs_inode_extref_name_len(leaf, extref);
+			cur_offset += btrfs_inode_extref_name_len(eb, extref);
 			cur_offset += sizeof(*extref);
 		}
 		btrfs_tree_read_unlock_blocking(eb);


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