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

[Manish Rangankar]

> -----Original Message-----
> From: Zheng Hacker <hackerzheng666@xxxxxxxxx>
> Sent: Thursday, March 23, 2023 9:15 AM
> To: Mike Christie <michael.christie@xxxxxxxxxx>
> Cc: Zheng Wang <zyytlz.wz@xxxxxxx>; Nilesh Javali <njavali@xxxxxxxxxxx>;
> Manish Rangankar <mrangankar@xxxxxxxxxxx>; GR-QLogic-Storage-
> Upstream <GR-QLogic-Storage-Upstream@xxxxxxxxxxx>;
> jejb@xxxxxxxxxxxxx; martin.petersen@xxxxxxxxxx; linux-
> scsi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> 1395428693sheep@xxxxxxxxx; alex000young@xxxxxxxxx
> Subject: [EXT] Re: [PATCH RESEND] scsi: qedi: Fix use after free bug in
> qedi_remove due to race condition
> 
> External Email
> 
> ----------------------------------------------------------------------
> 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
> >

Best place to call cancel_delayed_work_sync is after qedi_ops->stop(qedi->cdev) and 
qedi_ops->ll2->stop(qedi->cdev);, after these qed calls firmware will not post any events to qedi driver.

Thanks,
Manish