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

Greg Kroah-Hartman
2015-10-23T17:47:14Z

From: Chris Mason <clm@fb.com>

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@fb.com>
cc: Mark Fasheh <mfasheh@suse.de>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Mark Fasheh <mfasheh@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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);