Re: [PATCH RESEND] scsi: qedi: Fix use after free bug in qedi_remove due to race condition

[Zheng Hacker]

Mike Christie <michael.christie@xxxxxxxxxx> 于2023年3月21日周二 00:11写道：
>
> On 3/18/23 3:13 AM, Zheng Wang wrote:
> > In qedi_probe, it calls __qedi_probe, which bound &qedi->recovery_work
> > with qedi_recovery_handler and bound &qedi->board_disable_work
> > with qedi_board_disable_work.
> >
> > When it calls qedi_schedule_recovery_handler, it will finally
> > call schedule_delayed_work to start the work.
> >
> > When we call qedi_remove to remove the driver, there
> > may be a sequence as follows:
> >
> > Fix it by finishing the work before cleanup in qedi_remove.
> >
> > CPU0                  CPU1
> >
> >                      |qedi_recovery_handler
> > qedi_remove          |
> >   __qedi_remove      |
> > iscsi_host_free      |
> > scsi_host_put        |
> > //free shost         |
> >                      |iscsi_host_for_each_session
> >                      |//use qedi->shost
> >
> > Fixes: 4b1068f5d74b ("scsi: qedi: Add MFW error recovery process")
> > Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
> > ---
> >  drivers/scsi/qedi/qedi_main.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/scsi/qedi/qedi_main.c b/drivers/scsi/qedi/qedi_main.c
> > index f2ee49756df8..25223f6f5344 100644
> > --- a/drivers/scsi/qedi/qedi_main.c
> > +++ b/drivers/scsi/qedi/qedi_main.c
> > @@ -2414,6 +2414,10 @@ static void __qedi_remove(struct pci_dev *pdev, int mode)
> >       int rval;
> >       u16 retry = 10;
> >
> > +     /*cancel work*/
>
> This comment is not needed. The name of the functions you are calling have
> "cancel" and "work" in them so we know. If you want to add a comment explain
> why the cancel calls are needed here.
>

Hi,

Sorry for my late reply and thanks for your advice. Will remove it in
the next version of patch.

>
> > +     cancel_delayed_work_sync(&qedi->recovery_work);
> > +     cancel_delayed_work_sync(&qedi->board_disable_work);
>
>
> How do you know after you have called cancel_delayed_work_sync that
> schedule_recovery_handler or schedule_hw_err_handler can't be called?
> I don't know the qed driver well, but it looks like you could have
> operations still running, so after you cancel here one of those ops
> could lead to them scheduling the work again.
>

Sorry I didn't know how to make sure there's no more schedule. But I do think
this is important. Maybe there're someone else who can give us advice.

Best regards,
Zheng
>
> > +
> >       if (mode == QEDI_MODE_NORMAL)
> >               iscsi_host_remove(qedi->shost, false);
> >       else if (mode == QEDI_MODE_SHUTDOWN)
>