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

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Date:   Thu, 8 Jul 2021 15:14:24 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Jan Beulich <jbeulich@...e.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Roger Pau Monné <roger.pau@...rix.com>,
        Jens Axboe <axboe@...nel.dk>, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH v2 3/3] xen/blkfront: don't trust the backend response
 data blindly

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@...e.com>
> 
> Reviewed-by: Jan Beulich <jbeulich@...e.com>
> 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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