Commit 26b7c0ac authored Aug 23, 2022 by Filipe Manana Committed by Greg Kroah-Hartman Oct 26, 2022

btrfs: fix race between quota enable and quota rescan ioctl



commit 331cd9461412e103d07595a10289de90004ac890 upstream.

When enabling quotas, at btrfs_quota_enable(), after committing the
transaction, we change fs_info->quota_root to point to the quota root we
created and set BTRFS_FS_QUOTA_ENABLED at fs_info->flags. Then we try
to start the qgroup rescan worker, first by initializing it with a call
to qgroup_rescan_init() - however if that fails we end up freeing the
quota root but we leave fs_info->quota_root still pointing to it, this
can later result in a use-after-free somewhere else.

We have previously set the flags BTRFS_FS_QUOTA_ENABLED and
BTRFS_QGROUP_STATUS_FLAG_ON, so we can only fail with -EINPROGRESS at
btrfs_quota_enable(), which is possible if someone already called the
quota rescan ioctl, and therefore started the rescan worker.

So fix this by ignoring an -EINPROGRESS and asserting we can't get any
other error.

Reported-by: Ye Bin <yebin10@huawei.com>
Link: https://lore.kernel.org/linux-btrfs/20220823015931.421355-1-yebin10@huawei.com/


CC: stable@vger.kernel.org # 4.19+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 3742e9fd

fs/btrfs/qgroup.c

+15 −0

Original line number	Diff line number	Diff line
		@@ -1075,6 +1075,21 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info)
		fs_info->qgroup_rescan_running = true;
		btrfs_queue_work(fs_info->qgroup_rescan_workers,
		&fs_info->qgroup_rescan_work);
		} else {
		/*
		* We have set both BTRFS_FS_QUOTA_ENABLED and
		* BTRFS_QGROUP_STATUS_FLAG_ON, so we can only fail with
		* -EINPROGRESS. That can happen because someone started the
		* rescan worker by calling quota rescan ioctl before we
		* attempted to initialize the rescan worker. Failure due to
		* quotas disabled in the meanwhile is not possible, because
		* we are holding a write lock on fs_info->subvol_sem, which
		* is also acquired when disabling quotas.
		* Ignore such error, and any other error would need to undo
		* everything we did in the transaction we just committed.
		*/
		ASSERT(ret == -EINPROGRESS);
		ret = 0;
		}

		out_free_path: