linux-kernel - Re: [PATCH] mptsas: fix undefined behaviour of a shift of an int by more than 31 places

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Date:   Thu, 9 May 2019 17:30:39 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     James Bottomley <James.Bottomley@...senPartnership.com>,
        Colin Ian King <colin.king@...onical.com>,
        Sathya Prakash <sathya.prakash@...adcom.com>,
        Chaitra P B <chaitra.basappa@...adcom.com>,
        Suganath Prabu Subramani 
        <suganath-prabu.subramani@...adcom.com>,
        MPT-FusionLinux.pdl@...adcom.com, linux-scsi@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mptsas: fix undefined behaviour of a shift of an int by
 more than 31 places

On 5/8/19 4:24 PM, James Bottomley wrote:
> On Wed, 2019-05-08 at 14:07 +0100, Colin Ian King wrote:
>> On 05/05/2019 04:34, James Bottomley wrote:
>>> On Sat, 2019-05-04 at 17:40 +0100, Colin King wrote:
>>>> From: Colin Ian King <colin.king@...onical.com>
>>>>
>>>> Currently the shift of int value 1 by more than 31 places can
>>>> result in undefined behaviour. Fix this by making the 1 a ULL
>>>> value before the shift operation.
>>>
>>> Fusion SAS is pretty ancient.  I thought the largest one ever
>>> produced had four phys, so how did you produce the overflow?
>>
>> This was an issue found by static analysis with Coverity; so I guess
>> won't happen in the wild, in which case the patch could be ignored.
> 
> The point I was more making is that if we thought this could ever
> happen in practice, we'd need more error handling than simply this:
> we'd be setting the phy_bitmap to zero which would be every bit as bad
> as some random illegal value.
> 
Thing is, mptsas is used as the default emulation in VMWare, and that 
does allow you to do some pretty weird configurations (I've found myself 
fixing a bug with SATA hotplug on mptsas once ...).
So I wouldn't discard this issue out of hand.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke            Teamlead Storage & Networking
hare@...e.de                              +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)