Re: [PATCH V3 01/17] ublk: validate ublk server pid

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

On Tue, Jul 15, 2025 at 10:50:39AM -0400, Caleb Sander Mateos wrote:
> On Sun, Jul 13, 2025 at 10:34 AM Ming Lei <ming.lei@redhat.com> wrote:
> >
> > ublk server pid(the `tgid` of the process opening the ublk device) is stored
> > in `ublk_device->ublksrv_tgid`. This `tgid` is then checked against the
> > `ublksrv_pid` in `ublk_ctrl_start_dev` and `ublk_ctrl_end_recovery`.
> >
> > This ensures that correct ublk server pid is stored in device info.
> >
> > Fixes: 71f28f3136af ("ublk_drv: add io_uring based userspace block driver")
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> >  drivers/block/ublk_drv.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> > index a1a700c7e67a..2b894de29823 100644
> > --- a/drivers/block/ublk_drv.c
> > +++ b/drivers/block/ublk_drv.c
> > @@ -237,6 +237,7 @@ struct ublk_device {
> >         unsigned int            nr_privileged_daemon;
> >         struct mutex cancel_mutex;
> >         bool canceling;
> > +       pid_t   ublksrv_tgid;
> >  };
> >
> >  /* header of ublk_params */
> > @@ -1528,6 +1529,7 @@ static int ublk_ch_open(struct inode *inode, struct file *filp)
> >         if (test_and_set_bit(UB_STATE_OPEN, &ub->state))
> >                 return -EBUSY;
> >         filp->private_data = ub;
> > +       ub->ublksrv_tgid = current->tgid;
> >         return 0;
> >  }
> >
> > @@ -1542,6 +1544,7 @@ static void ublk_reset_ch_dev(struct ublk_device *ub)
> >         ub->mm = NULL;
> >         ub->nr_queues_ready = 0;
> >         ub->nr_privileged_daemon = 0;
> > +       ub->ublksrv_tgid = -1;
> 
> Should this be reset to 0? The next patch checks whether ublksrv_tgid
> is 0 in ublk_timeout().

No, swapper pid is 0.

The check in next patch just tries to double check if ublk char device
is opened.

> Also, the accesses to it should probably be
> using {READ,WRITE}_ONCE() since ublk server open/close can happen
> concurrently with ublk I/O timeout handling.

ublk_abort_queue() is called in ublk_ch_release(), and any inflight request
is either requeued or failed, so ublk I/O timeout handling won't happen
concurrently with ublk char open()/close().


Thanks, 
Ming