linux-kernel - Re: [PATCH 4/4] xen/scsifront: harden driver against malicious backend

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Date:   Thu, 21 Apr 2022 12:13:14 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH 4/4] xen/scsifront: harden driver against malicious
 backend

On 20.04.22 18:13, Boris Ostrovsky wrote:
> Just a couple of nits.
> 
> 
> On 4/20/22 5:25 AM, Juergen Gross wrote:
>> -static int scsifront_ring_drain(struct vscsifrnt_info *info)
>> +static int scsifront_ring_drain(struct vscsifrnt_info *info,
>> +                unsigned int *eoiflag)
>>   {
>> -    struct vscsiif_response *ring_rsp;
>> +    struct vscsiif_response ring_rsp;
>>       RING_IDX i, rp;
>>       int more_to_do = 0;
>> -    rp = info->ring.sring->rsp_prod;
>> -    rmb();    /* ordering required respective to dom0 */
>> +    rp = READ_ONCE(info->ring.sring->rsp_prod);
>> +    virt_rmb();    /* ordering required respective to backend */
>> +    if (RING_RESPONSE_PROD_OVERFLOW(&info->ring, rp)) {
>> +        scsifront_set_error(info, "illegal number of responses");
> 
> 
> In net and block drivers we report number of such responses. (But not in usb)
I'm not sure the specific value is of any interest.

>> +        return 0;
>> +    }
>>       for (i = info->ring.rsp_cons; i != rp; i++) {
>> -        ring_rsp = RING_GET_RESPONSE(&info->ring, i);
>> -        scsifront_do_response(info, ring_rsp);
>> +        RING_COPY_RESPONSE(&info->ring, i, &ring_rsp);
>> +        scsifront_do_response(info, &ring_rsp);
>> +        if (info->host_active == STATE_ERROR)
>> +            return 0;
>> +        *eoiflag = 0;
> 
> 
> *eoiflags &= ~XEN_EOI_FLAG_SPURIOUS; ?

Yes, probably better.

> We also use eoi_flags name in other instances in this file.

I'll unify the name.


Juergen

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