linux-kernel - Re: [PATCH] zram: set physical queue limits to avoid array out of bounds accesses

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Date:   Tue, 7 Mar 2017 08:00:30 +0100
From:   Hannes Reinecke <hare@...e.de>
To:     Minchan Kim <minchan@...nel.org>,
        Johannes Thumshirn <jthumshirn@...e.de>
Cc:     Jens Axboe <axboe@...com>, Nitin Gupta <ngupta@...are.org>,
        Christoph Hellwig <hch@....de>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        yizhan@...hat.com,
        Linux Block Layer Mailinglist <linux-block@...r.kernel.org>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] zram: set physical queue limits to avoid array out of
 bounds accesses

On 03/07/2017 06:22 AM, Minchan Kim wrote:
> Hello Johannes,
> 
> On Mon, Mar 06, 2017 at 11:23:35AM +0100, Johannes Thumshirn wrote:
>> zram can handle at most SECTORS_PER_PAGE sectors in a bio's bvec. When using
>> the NVMe over Fabrics loopback target which potentially sends a huge bulk of
>> pages attached to the bio's bvec this results in a kernel panic because of
>> array out of bounds accesses in zram_decompress_page().
> 
> First of all, thanks for the report and fix up!
> Unfortunately, I'm not familiar with that interface of block layer.
> 
> It seems this is a material for stable so I want to understand it clear.
> Could you say more specific things to educate me?
> 
> What scenario/When/How it is problem?  It will help for me to understand!
> 
The problem is that zram as it currently stands can only handle bios
where each bvec contains a single page (or, to be precise, a chunk of
data with a length of a page).

This is not an automatic guarantee from the block layer (who is free to
send us bios with arbitrary-sized bvecs), so we need to set the queue
limits to ensure that.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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