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Message-ID: <df87b66cc9de4f4c8e3b555278533b0d@AcuMS.aculab.com>
Date: Mon, 17 Jul 2023 13:17:34 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Jason-JH Lin (林睿祥)'
<Jason-JH.Lin@...iatek.com>,
CK Hu (胡俊光) <ck.hu@...iatek.com>,
"amergnat@...libre.com" <amergnat@...libre.com>,
"chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
"angelogioacchino.delregno@...labora.com"
<angelogioacchino.delregno@...labora.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mediatek@...ts.infradead.org"
<linux-mediatek@...ts.infradead.org>,
Singo Chang (張興國)
<Singo.Chang@...iatek.com>,
Johnson Wang (王聖鑫)
<Johnson.Wang@...iatek.com>,
Jason-ch Chen (陳建豪)
<Jason-ch.Chen@...iatek.com>,
Shawn Sung (宋孝謙)
<Shawn.Sung@...iatek.com>,
Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>,
"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
Project_Global_Chrome_Upstream_Group
<Project_Global_Chrome_Upstream_Group@...iatek.com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"matthias.bgg@...il.com" <matthias.bgg@...il.com>
Subject: RE: [PATCH v3 3/4] drm/mediatek: Add casting before assign
From: Jason-JH Lin
> Sent: 14 July 2023 07:46
>
> Hi CK,
>
> Thanks for the reviews.
>
> On Fri, 2023-07-14 at 05:45 +0000, CK Hu (胡俊光) wrote:
> > Hi, Jason:
> >
> > On Wed, 2023-06-21 at 18:22 +0800, Jason-JH.Lin wrote:
> > > 1. Add casting before assign to avoid the unintentional integer
> > > overflow or unintended sign extension.
> > > 2. Add a int varriable for multiplier calculation instead of
> > > calculating
> > > different types multiplier with dma_addr_t varriable directly.
> >
> > I agree with these modification, but the title does not match the
> > modification.
> >
> > Regards,
> > CK
>
> I'll change the title and commit msg at the next version below:
>
> Fix unintentional integer overflow in multiplying different types
>
> 1. Instead of multiplying 2 variable of different types. Change to
> assign a value of one variable and then multiply the other variable.
>
> 2. Add a int variable for multiplier calculation instead of calculating
> different types multiplier with dma_addr_t variable directly.
I'm pretty sure the patch makes absolutely no difference.
In C all arithmetic is done with char/short (inc. unsigned)
promoted to int.
So the only likely overflow is if the values exceed 2^31.
Since the temporaries you are using are 'int' this isn't true.
David
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