btrfs: Fix use-after-free when cleaning up fs_devs with a single stale device

commit fd649f10c3d21ee9d7542c609f29978bdf73ab94 upstream.

Commit 4fde46f0cc71 ("Btrfs: free the stale device") introduced
btrfs_free_stale_device which iterates the device lists for all
registered btrfs filesystems and deletes those devices which aren't
mounted. In a btrfs_devices structure has only 1 device attached to it
and it is unused then btrfs_free_stale_devices will proceed to also free
the btrfs_fs_devices struct itself. Currently this leads to a use after
free since list_for_each_entry will try to perform a check on the
already freed memory to see if it has to terminate the loop.

The fix is to use 'break' when we know we are freeing the current
fs_devs.

Fixes: 4fde46f0cc71 ("Btrfs: free the stale device")
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 87890c7d4b5e6f819ab5899e8cf5aa4086199ec3..8bd34024744c54cd5a8bb9611657269cf88626f9 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -589,6 +589,7 @@ void btrfs_free_stale_device(struct btrfs_device *cur_dev)
                                btrfs_sysfs_remove_fsid(fs_devs);
                                list_del(&fs_devs->list);
                                free_fs_devices(fs_devs);
+                               break;
                        } else {
                                fs_devs->num_devices--;
                                list_del(&dev->dev_list);