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Subject: Re: [PATCH v2 3/3] xen/blkfront: don't trust the backend response
 data blindly
To:     Jan Beulich <jbeulich@suse.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>,
        Jens Axboe <axboe@kernel.dk>, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org, linux-block@vger.kernel.org
References: <20210708124345.10173-1-jgross@suse.com>
 <20210708124345.10173-4-jgross@suse.com>
 <c33d7570-d986-749d-1e4f-85829a11babb@suse.com>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <49aa4ddb-ca58-e0df-0675-daa72866d3db@suse.com>
Date:   Thu, 8 Jul 2021 15:14:24 +0200
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From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
 Stefano Stabellini <sstabellini@kernel.org>,
 Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
 =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>,
 Jens Axboe <axboe@kernel.dk>, xen-devel@lists.xenproject.org,
 linux-kernel@vger.kernel.org, linux-block@vger.kernel.org
Message-ID: <49aa4ddb-ca58-e0df-0675-daa72866d3db@suse.com>
Subject: Re: [PATCH v2 3/3] xen/blkfront: don't trust the backend response
 data blindly
References: <20210708124345.10173-1-jgross@suse.com>
 <20210708124345.10173-4-jgross@suse.com>
 <c33d7570-d986-749d-1e4f-85829a11babb@suse.com>
In-Reply-To: <c33d7570-d986-749d-1e4f-85829a11babb@suse.com>

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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 maliciou=
s
>> 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 fro=
m
>> 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@suse.com>
>=20
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> albeit ...
>=20
>> @@ -1602,7 +1628,8 @@ static irqreturn_t blkif_interrupt(int irq, void=
 *dev_id)
>>   		case BLKIF_OP_DISCARD:
>>   			if (unlikely(bret.status =3D=3D BLKIF_RSP_EOPNOTSUPP)) {
>>   				struct request_queue *rq =3D 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 =3D BLK_STS_NOTSUPP;
>>   				info->feature_discard =3D 0;
>> @@ -1614,13 +1641,13 @@ static irqreturn_t blkif_interrupt(int irq, vo=
id *dev_id)
>>   		case BLKIF_OP_FLUSH_DISKCACHE:
>>   		case BLKIF_OP_WRITE_BARRIER:
>>   			if (unlikely(bret.status =3D=3D 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 =3D BLK_STS_NOTSUPP;
>>   			}
>>   			if (unlikely(bret.status =3D=3D BLKIF_RSP_ERROR &&
>>   				     rinfo->shadow[id].req.u.rw.nr_segments =3D=3D 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 =3D 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 !=3D 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);
>>  =20
>>   			break;
>>   		default:
>=20
> ... 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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