Re: [PATCH v2] ublk: fix ublksrv pid handling for pid namespaces

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

On Mon, Jan 12, 2026 at 02:56:14PM -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
> 
>  drivers/block/ublk_drv.c | 30 +++++++++++++++++++++++++++++-
>  1 file changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 79847e0b9e88..4a4673e64668 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -2922,6 +2922,10 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub,
>  	if (wait_for_completion_interruptible(&ub->completion) != 0)
>  		return -EINTR;
>  
> +	rcu_read_lock();
> +	ublksrv_pid = pid_nr(find_vpid(ublksrv_pid));
> +	rcu_read_unlock();
> +

`ublksrv_pid` is from userspace, so it may be invalid, then you may have to
check result of find_vpid().

>  	if (ub->ublksrv_tgid != ublksrv_pid)
>  		return -EINVAL;

Please add one helper of ublk_validate_ublksrv_pid() by moving all above
change into the helper, then two code paths can use the single helper.


Otherwise, this patch looks fine.

Thanks, 
Ming