From: Jan Beulich <jbeulich@suse.com>
To: Paul Durrant <paul@xen.org>
Cc: "Paul Durrant" <pdurrant@amazon.com>,
"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
"Roger Pau Monné" <roger.pau@citrix.com>,
"Jens Axboe" <axboe@kernel.dk>,
"Dongli Zhang" <dongli.zhang@oracle.com>,
linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH] xen-blkback: fix compatibility bug with single page rings
Date: Wed, 27 Jan 2021 11:56:56 +0100 [thread overview]
Message-ID: <cd70ae5e-a389-7521-8caf-15650a276152@suse.com> (raw)
In-Reply-To: <20210127103034.2559-1-paul@xen.org>
On 27.01.2021 11:30, Paul Durrant wrote:
> From: Paul Durrant <pdurrant@amazon.com>
>
> Prior to commit 4a8c31a1c6f5 ("xen/blkback: rework connect_ring() to avoid
> inconsistent xenstore 'ring-page-order' set by malicious blkfront"), the
> behaviour of xen-blkback when connecting to a frontend was:
>
> - read 'ring-page-order'
> - if not present then expect a single page ring specified by 'ring-ref'
> - else expect a ring specified by 'ring-refX' where X is between 0 and
> 1 << ring-page-order
>
> This was correct behaviour, but was broken by the afforementioned commit to
> become:
>
> - read 'ring-page-order'
> - if not present then expect a single page ring
> - expect a ring specified by 'ring-refX' where X is between 0 and
> 1 << ring-page-order
> - if that didn't work then see if there's a single page ring specified by
> 'ring-ref'
>
> This incorrect behaviour works most of the time but fails when a frontend
> that sets 'ring-page-order' is unloaded and replaced by one that does not
> because, instead of reading 'ring-ref', xen-blkback will read the stale
> 'ring-ref0' left around by the previous frontend will try to map the wrong
> grant reference.
>
> This patch restores the original behaviour.
Isn't this only the 2nd of a pair of fixes that's needed, the
first being the drivers, upon being unloaded, to fully clean up
after itself? Any stale key left may lead to confusion upon
re-use of the containing directory.
Jan
next prev parent reply other threads:[~2021-01-27 11:02 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-27 10:30 [PATCH] xen-blkback: fix compatibility bug with single page rings Paul Durrant
2021-01-27 10:56 ` Jan Beulich [this message]
2021-01-27 11:09 ` Paul Durrant
2021-01-27 11:20 ` Jan Beulich
2021-01-27 11:33 ` Paul Durrant
2021-01-27 11:37 ` Jan Beulich
2021-01-27 19:57 ` Dongli Zhang
2021-01-28 8:30 ` Paul Durrant
2021-01-28 12:55 Paul Durrant
2021-01-28 13:04 ` Paul Durrant
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