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

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Message-ID: <1557325468.3196.2.camel@HansenPartnership.com>
Date:   Wed, 08 May 2019 07:24:28 -0700
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     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 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.

James