btrfs: fix use after free iterating extrefs

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@fb.com>
cc: stable@vger.kernel.org # v3.7+
cc: Mark Fasheh <mfasheh@suse.de>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Mark Fasheh <mfasheh@suse.de>

1 files changed, 3 insertions, 5 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index ecbc63d3143e..9a2ec79e8cfb 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -1828,7 +1828,6 @@ static int iterate_inode_extrefs(u64 inum, struct btrfs_root *fs_root,
         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;
@@ -1856,9 +1855,8 @@ static int iterate_inode_extrefs(u64 inum, struct btrfs_root *fs_root,
                 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) {
@@ -1872,7 +1870,7 @@ static int iterate_inode_extrefs(u64 inum, struct btrfs_root *fs_root,
                         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);