Re: [PATCH v2 3/3] xen/blkfront: don't trust the backend response data blindly

[Juergen Gross <jgross@xxxxxxxx>]

On 08.07.21 15:11, Jan Beulich wrote:
> On 08.07.2021 14:43, Juergen Gross wrote:
> > Today blkfront will trust the backend to send only sane response data.
> > In order to avoid privilege escalations or crashes in case of malicious
> > backends verify the data to be within expected limits. Especially make
> > sure that the response always references an outstanding request.
> >
> > Introduce a new state of the ring BLKIF_STATE_ERROR which will be
> > switched to in case an inconsistency is being detected. Recovering from
> > this state is possible only via removing and adding the virtual device
> > again (e.g. via a suspend/resume cycle).
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> albeit ...
>
> > @@ -1602,7 +1628,8 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
> >                 case BLKIF_OP_DISCARD:
> >                         if (unlikely(bret.status == BLKIF_RSP_EOPNOTSUPP)) {
> >                                 struct request_queue *rq = info->rq;
> > -                               printk(KERN_WARNING "blkfront: %s: %s op 
> > failed\n",
> > +
> > +                               pr_warn_ratelimited("blkfront: %s: %s op 
> > failed\n",
> >                                            info->gd->disk_name, 
> > op_name(bret.operation));
> >                                 blkif_req(req)->error = BLK_STS_NOTSUPP;
> >                                 info->feature_discard = 0;
> > @@ -1614,13 +1641,13 @@ static irqreturn_t blkif_interrupt(int irq, void 
> > *dev_id)
> >                 case BLKIF_OP_FLUSH_DISKCACHE:
> >                 case BLKIF_OP_WRITE_BARRIER:
> >                         if (unlikely(bret.status == BLKIF_RSP_EOPNOTSUPP)) {
> > -                               printk(KERN_WARNING "blkfront: %s: %s op 
> > failed\n",
> > +                               pr_warn_ratelimited("blkfront: %s: %s op 
> > failed\n",
> >                                        info->gd->disk_name, 
> > op_name(bret.operation));
> >                                 blkif_req(req)->error = BLK_STS_NOTSUPP;
> >                         }
> >                         if (unlikely(bret.status == BLKIF_RSP_ERROR &&
> >                                      rinfo->shadow[id].req.u.rw.nr_segments == 
> > 0)) {
> > -                               printk(KERN_WARNING "blkfront: %s: empty %s op 
> > failed\n",
> > +                               pr_warn_ratelimited("blkfront: %s: empty %s op 
> > failed\n",
> >                                        info->gd->disk_name, 
> > op_name(bret.operation));
> >                                 blkif_req(req)->error = BLK_STS_NOTSUPP;
> >                         }
> > @@ -1635,8 +1662,8 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
> >                 case BLKIF_OP_READ:
> >                 case BLKIF_OP_WRITE:
> >                         if (unlikely(bret.status != BLKIF_RSP_OKAY))
> > -                               dev_dbg(&info->xbdev->dev, "Bad return from blkdev 
> > data "
> > -                                       "request: %x\n", bret.status);
> > +                               dev_dbg_ratelimited(&info->xbdev->dev,
> > +                                       "Bad return from blkdev data request: 
> > %x\n", bret.status);
> >   
> >   			break;
> >                 default:
> ... all of these look kind of unrelated to the topic of the patch,
> and the conversion also isn't mentioned as on-purpose in the
> description.
Hmm, yes, I'll add a sentence to the commit message.


Juergen

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