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

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Date:   Wed, 20 Apr 2022 12:13:50 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.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

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)


> +		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; ?


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


-boris