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    Subject[PATCH 6.0 120/862] btrfs: fix race between quota enable and quota rescan ioctl
    Date
    From: Filipe Manana <fdmanana@suse.com>

    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>
    ---
    fs/btrfs/qgroup.c | 15 +++++++++++++++
    1 file changed, 15 insertions(+)

    --- a/fs/btrfs/qgroup.c
    +++ b/fs/btrfs/qgroup.c
    @@ -1174,6 +1174,21 @@ out_add_root:
    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:

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