Re: [PATCH v3] ublk: fix ublksrv pid handling for pid namespaces

[Ming Lei <ming.lei@redhat.com>]

On Wed, Jan 14, 2026 at 12:47:04PM -0800, Seamus Connor wrote:
> When ublksrv runs inside a pid namespace, START/END_RECOVERY compared
> the stored init-ns tgid against the userspace pid (getpid vnr), so the
> check failed and control ops could not proceed. Compare against the
> caller’s init-ns tgid and store that value, then translate it back to
> the caller’s pid namespace when reporting GET_DEV_INFO so ublk list
> shows a sensible pid.
> 
> Testing: start/recover in a pid namespace; `ublk list` shows
> reasonable pid values in init, child, and sibling namespaces.
> 
> Fixes: d37a224fc119 ("ublk: validate ublk server pid")
> Signed-off-by: Seamus Connor <sconnor@purestorage.com>
> Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
> ---
> Changes since v1:
>  - Updated start_dev and end_recovery to respect the user-supplied pid
> 
> Changes since v2:
>  - Moved pid translation into a helper function
> 
>  drivers/block/ublk_drv.c | 35 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 67d4a867aec4..01747d256ff5 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -2852,6 +2852,15 @@ static struct ublk_device *ublk_get_device_from_id(int idx)
>  	return ub;
>  }
>  
> +static pid_t ublk_translate_user_pid(pid_t ublksrv_pid)
> +{
> +	rcu_read_lock();
> +	ublksrv_pid = pid_nr(find_vpid(ublksrv_pid));
> +	rcu_read_unlock();
> +
> +	return ublksrv_pid;
> +}
> +
>  static int ublk_ctrl_start_dev(struct ublk_device *ub,
>  		const struct ublksrv_ctrl_cmd *header)
>  {
> @@ -2920,6 +2929,8 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub,
>  	if (wait_for_completion_interruptible(&ub->completion) != 0)
>  		return -EINTR;
>  
> +	ublksrv_pid = ublk_translate_user_pid(ublksrv_pid);
> +
>  	if (ub->ublksrv_tgid != ublksrv_pid)
>  		return -EINVAL;

The above two lines can be moved to the helper which can be renamed as ublk_validate_user_pid(),
otherwise this patch looks good:

Reviewed-by: Ming Lei <ming.lei@redhat.com>


Thanks, 
Ming