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>

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index ecbc63d..9a2ec79 100644 (file)
--- 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);