Commit 801660b0 authored Aug 06, 2018 by Anand Jain Committed by David Sterba Aug 23, 2018

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>

parent a5b7f429

fs/btrfs/volumes.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -4491,7 +4491,12 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)

		/* Now btrfs_update_device() will change the on-disk size. */
		ret = btrfs_update_device(trans, device);
		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) {