btrfs: btrfs_shrink_device should call commit transaction at the end

Test case btrfs/164 reports use-after-free:

[ 6712.084324] general protection fault: 0000 [#1] PREEMPT SMP
..
[ 6712.195423]  btrfs_update_commit_device_size+0x75/0xf0 [btrfs]
[ 6712.201424]  btrfs_commit_transaction+0x57d/0xa90 [btrfs]
[ 6712.206999]  btrfs_rm_device+0x627/0x850 [btrfs]
[ 6712.211800]  btrfs_ioctl+0x2b03/0x3120 [btrfs]

Reason for this is that btrfs_shrink_device adds the resized device to
the fs_devices::resized_devices after it has called the last commit
transaction.

So the list fs_devices::resized_devices is not empty when
btrfs_shrink_device returns.  Now the parent function
btrfs_rm_device calls:

        btrfs_close_bdev(device);
        call_rcu(&device->rcu, free_device_rcu);

and then does the transactio ncommit. It goes through the
fs_devices::resized_devices in btrfs_update_commit_device_size and
leads to use-after-free.

Fix this by making sure btrfs_shrink_device calls the last needed
btrfs_commit_transaction before the return. This is consistent with what
the grow counterpart does and this makes sure the on-disk state is
persistent when the function returns.

Reported-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
Tested-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index da86706123ffa4d85ce19148be2157edb9d7d3a4..f4405e430da6e003306e1a4d471731e1a13c9230 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4491,7 +4491,12 @@ again:
 
        /* Now btrfs_update_device() will change the on-disk size. */
        ret = btrfs_update_device(trans, device);
-       btrfs_end_transaction(trans);
+       if (ret < 0) {
+               btrfs_abort_transaction(trans, ret);
+               btrfs_end_transaction(trans);
+       } else {
+               ret = btrfs_commit_transaction(trans);
+       }
 done:
        btrfs_free_path(path);
        if (ret) {