linux-kernel - Re: [Xen-devel] [PATCH v6 2/2] xen/blkback: rework connect_ring() to avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront

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Date:   Tue, 15 Jan 2019 09:20:36 +0100
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>
CC:     <xen-devel@...ts.xenproject.org>, <linux-block@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <axboe@...nel.dk>,
        <Paul.Durrant@...rix.com>, <konrad.wilk@...cle.com>
Subject: Re: [Xen-devel] [PATCH v6 2/2] xen/blkback: rework connect_ring() to
 avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront

On Tue, Jan 15, 2019 at 12:41:44AM +0800, Dongli Zhang wrote:
> The xenstore 'ring-page-order' is used globally for each blkback queue and
> therefore should be read from xenstore only once. However, it is obtained
> in read_per_ring_refs() which might be called multiple times during the
> initialization of each blkback queue.
> 
> If the blkfront is malicious and the 'ring-page-order' is set in different
> value by blkfront every time before blkback reads it, this may end up at
> the "WARN_ON(i != (XEN_BLKIF_REQS_PER_PAGE * blkif->nr_ring_pages));" in
> xen_blkif_disconnect() when frontend is destroyed.
> 
> This patch reworks connect_ring() to read xenstore 'ring-page-order' only
> once.
> 
> Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>

LGTM:

Reviewed-by: Roger Pau Monné <roger.pau@...rix.com>

Thanks!