Re: [PATCH v2 3/7] loop: use ns_capable for some loop operations

["Serge E. Hallyn" <serge@hallyn.com>]

On Wed, Apr 22, 2020 at 04:54:33PM +0200, Christian Brauner wrote:
> The following  LOOP_GET_STATUS, LOOP_SET_STATUS, and LOOP_SET_BLOCK_SIZE
> operations are now allowed in non-initial namespaces. Most other
> operations were already possible before.
> 
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Seth Forshee <seth.forshee@canonical.com>
> Cc: Tom Gundersen <teg@jklm.no>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Christian Kellner <ckellner@redhat.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: David Rheinsberg <david.rheinsberg@gmail.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Reviewed-by: Serge Hallyn <serge@hallyn.com>

> ---
> /* v2 */
> - Christian Brauner <christian.brauner@ubuntu.com>:
>   - Adapated loop_capable() based on changes in the loopfs
>     implementation patchset. Otherwise it is functionally equivalent to
>     the v1 version.
> ---
>  drivers/block/loop.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 52f7583dd17d..8e21d4b33e01 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1352,6 +1352,16 @@ void loopfs_evict_locked(struct loop_device *lo)
>  	}
>  	mutex_unlock(&loop_ctl_mutex);
>  }
> +
> +static bool loop_capable(const struct loop_device *lo, int cap)
> +{
> +	return ns_capable(loopfs_ns(lo), cap);
> +}
> +#else /* !CONFIG_BLK_DEV_LOOPFS */
> +static inline bool loop_capable(const struct loop_device *lo, int cap)
> +{
> +	return capable(cap);
> +}
>  #endif /* CONFIG_BLK_DEV_LOOPFS */
>  
>  static int
> @@ -1368,7 +1378,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>  		return err;
>  	if (lo->lo_encrypt_key_size &&
>  	    !uid_eq(lo->lo_key_owner, uid) &&
> -	    !capable(CAP_SYS_ADMIN)) {
> +	    !loop_capable(lo, CAP_SYS_ADMIN)) {
>  		err = -EPERM;
>  		goto out_unlock;
>  	}
> @@ -1499,7 +1509,7 @@ loop_get_status(struct loop_device *lo, struct loop_info64 *info)
>  	memcpy(info->lo_crypt_name, lo->lo_crypt_name, LO_NAME_SIZE);
>  	info->lo_encrypt_type =
>  		lo->lo_encryption ? lo->lo_encryption->number : 0;
> -	if (lo->lo_encrypt_key_size && capable(CAP_SYS_ADMIN)) {
> +	if (lo->lo_encrypt_key_size && loop_capable(lo, CAP_SYS_ADMIN)) {
>  		info->lo_encrypt_key_size = lo->lo_encrypt_key_size;
>  		memcpy(info->lo_encrypt_key, lo->lo_encrypt_key,
>  		       lo->lo_encrypt_key_size);
> @@ -1723,7 +1733,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
>  		return loop_clr_fd(lo);
>  	case LOOP_SET_STATUS:
>  		err = -EPERM;
> -		if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) {
> +		if ((mode & FMODE_WRITE) || loop_capable(lo, CAP_SYS_ADMIN)) {
>  			err = loop_set_status_old(lo,
>  					(struct loop_info __user *)arg);
>  		}
> @@ -1732,7 +1742,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
>  		return loop_get_status_old(lo, (struct loop_info __user *) arg);
>  	case LOOP_SET_STATUS64:
>  		err = -EPERM;
> -		if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) {
> +		if ((mode & FMODE_WRITE) || loop_capable(lo, CAP_SYS_ADMIN)) {
>  			err = loop_set_status64(lo,
>  					(struct loop_info64 __user *) arg);
>  		}
> @@ -1742,7 +1752,7 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
>  	case LOOP_SET_CAPACITY:
>  	case LOOP_SET_DIRECT_IO:
>  	case LOOP_SET_BLOCK_SIZE:
> -		if (!(mode & FMODE_WRITE) && !capable(CAP_SYS_ADMIN))
> +		if (!(mode & FMODE_WRITE) && !loop_capable(lo, CAP_SYS_ADMIN))
>  			return -EPERM;
>  		/* Fall through */
>  	default:
> -- 
> 2.26.1