linux-kernel - Re: [PATCH 4/8] xen/blkfront: don't trust the backend response data blindly

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Message-ID: <315ad8b9-8a98-8d3e-f66c-ab32af2731a8@suse.com>
Date:   Mon, 17 May 2021 16:11:05 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Roger Pau Monné <roger.pau@...rix.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Jens Axboe <axboe@...nel.dk>, xen-devel@...ts.xenproject.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] xen/blkfront: don't trust the backend response data
 blindly

On 13.05.2021 12:02, Juergen Gross wrote:
> @@ -1574,10 +1580,16 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
>  	spin_lock_irqsave(&rinfo->ring_lock, flags);
>   again:
>  	rp = rinfo->ring.sring->rsp_prod;
> +	if (RING_RESPONSE_PROD_OVERFLOW(&rinfo->ring, rp)) {
> +		pr_alert("%s: illegal number of responses %u\n",
> +			 info->gd->disk_name, rp - rinfo->ring.rsp_cons);
> +		goto err;
> +	}
>  	rmb(); /* Ensure we see queued responses up to 'rp'. */

I think you want to insert after the barrier.

> @@ -1680,6 +1707,11 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
>  	spin_unlock_irqrestore(&rinfo->ring_lock, flags);
>  
>  	return IRQ_HANDLED;
> +
> + err:
> +	info->connected = BLKIF_STATE_ERROR;
> +	pr_alert("%s disabled for further use\n", info->gd->disk_name);
> +	return IRQ_HANDLED;
>  }

Am I understanding that a suspend (and then resume) can be used to
recover from error state? If so - is this intentional? If so in turn,
would it make sense to spell this out in the description?

Jan