On 03/20/2018 07:45 AM, Misono, Tomohiro wrote:
> Deletion of subvolume by non-privileged user is completely restricted
> by default because we can delete a subvolume even if it is not empty
> and may cause data loss. In other words, when user_subvol_rm_allowed
> mount option is used, a user can delete a subvolume containing the
> directory which cannot be deleted directly by the user.
>
> However, there should be no harm to allow users to delete empty subvolumes
> when rmdir(2) would have been allowed if they were normal directories.
> This patch allows deletion of empty subvolume by default.
Instead of modifying the ioctl, what about allowing rmdir(2) to work for an
_empty_ subvolume (and all the permission check are satisfied) ?
>
> Note that user_subvol_rm_allowed option requires write+exec permission
> of the subvolume to be deleted, but they are not required for empty
> subvolume.
>
> The comment in the code is also updated accordingly.
>
> Signed-off-by: Tomohiro Misono <misono.tomoh...@jp.fujitsu.com>
> ---
> fs/btrfs/ioctl.c | 55 +++++++++++++++++++++++++++++++------------------------
> 1 file changed, 31 insertions(+), 24 deletions(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 111ee282b777..838406a7a7f5 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2366,36 +2366,43 @@ static noinline int btrfs_ioctl_snap_destroy(struct
> file *file,
> dest = BTRFS_I(inode)->root;
> if (!capable(CAP_SYS_ADMIN)) {
> /*
> - * Regular user. Only allow this with a special mount
> - * option, when the user has write+exec access to the
> - * subvol root, and when rmdir(2) would have been
> - * allowed.
> + * By default, regular user is only allowed to delete
> + * empty subvols when rmdir(2) would have been allowed
> + * if they were normal directories.
> *
> - * Note that this is _not_ check that the subvol is
> - * empty or doesn't contain data that we wouldn't
> + * If the mount option 'user_subvol_rm_allowed' is set,
> + * it allows users to delete non-empty subvols when the
> + * user has write+exec access to the subvol root and when
> + * rmdir(2) would have been allowed (except the emptiness
> + * check).
> + *
> + * Note that this option does _not_ check that if the subvol
> + * is empty or doesn't contain data that the user wouldn't
> * otherwise be able to delete.
> *
> - * Users who want to delete empty subvols should try
> - * rmdir(2).
> + * Users who want to delete empty subvols created by
> + * snapshot (ino number == 2) can use rmdir(2).
> */
> - err = -EPERM;
> - if (!btrfs_test_opt(fs_info, USER_SUBVOL_RM_ALLOWED))
> - goto out_dput;
> + err = -ENOTEMPTY;
> + if (inode->i_size != BTRFS_EMPTY_DIR_SIZE) {
> + if (!btrfs_test_opt(fs_info, USER_SUBVOL_RM_ALLOWED))
> + goto out_dput;
>
> - /*
> - * Do not allow deletion if the parent dir is the same
> - * as the dir to be deleted. That means the ioctl
> - * must be called on the dentry referencing the root
> - * of the subvol, not a random directory contained
> - * within it.
> - */
> - err = -EINVAL;
> - if (root == dest)
> - goto out_dput;
> + /*
> + * Do not allow deletion if the parent dir is the same
> + * as the dir to be deleted. That means the ioctl
> + * must be called on the dentry referencing the root
> + * of the subvol, not a random directory contained
> + * within it.
> + */
> + err = -EINVAL;
> + if (root == dest)
> + goto out_dput;
>
> - err = inode_permission(inode, MAY_WRITE | MAY_EXEC);
> - if (err)
> - goto out_dput;
> + err = inode_permission(inode, MAY_WRITE | MAY_EXEC);
> + if (err)
> + goto out_dput;
> + }
> }
>
> /* check if subvolume may be deleted by a user */
>
--
gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it>
Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5
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