Re: [PATCH-next] scsi: fix use-after-free problem in scsi_remove_target

[zhongjinghua]

在 2023/3/2 3:46, Bart Van Assche 写道:
> On 2/12/23 19:43, Zhong Jinghua wrote:
> > T0                            T1
> >   sdev_store_delete
> >    scsi_remove_device
> >     device_remove_file
> >      __scsi_remove_device
> >                              __iscsi_unbind_session
> >                               scsi_remove_target
> >                           spin_lock_irqsave
> >                                list_for_each_entry
> >       scsi_target_reap // starget->reaf 1 -> 0
>
> What is "reaf"? Did you perhaps want to write "reap_ref"?
Yes, I will modify late.
> > diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> > index e7893835b99a..0ad357ff4c59 100644
> > --- a/drivers/scsi/scsi_sysfs.c
> > +++ b/drivers/scsi/scsi_sysfs.c
> > @@ -1561,7 +1561,17 @@ void scsi_remove_target(struct device *dev)
> >               starget->state == STARGET_CREATED_REMOVE)
> >               continue;
> >           if (starget->dev.parent == dev || &starget->dev == dev) {
> > -            kref_get(&starget->reap_ref);
> > +
> > +            /*
> > +             * If starget->reap_ref is reduced to 0, it means
> > +             * that other processes are releasing it and
> > +             * there is no need to delete it again
> > +             */
> > +            if (!kref_get_unless_zero(&starget->reap_ref)) {
> > +                spin_unlock_irqrestore(shost->host_lock, flags);
> > +                goto restart;
> > +            }
> > +
> >               if (starget->state == STARGET_CREATED)
> >                   starget->state = STARGET_CREATED_REMOVE;
> >               else
>
> The above comment should be made more clear, e.g. as follows: "If the 
> reference count is already zero, skip this target. Calling 
> kref_get_unless_zero() if the reference count is zero is safe because 
> scsi_target_destroy() will wait until the host lock has been released 
> before freeing starget."

Agree. Thanks for your e.g.

I will send the v2 late.

> Otherwise this patch looks fine to me.
>
> Thanks,
>
> Bart.
Thanks,

Jinghua