linux-kernel - Re: [PATCH v2] mtd: blktrans: fix multiplication overflow

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Message-ID: <20150929002855.GR31505@google.com>
Date:	Mon, 28 Sep 2015 17:28:55 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Peng Fan <van.freenix@...il.com>
Cc:	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v2] mtd: blktrans: fix multiplication overflow

On Fri, Sep 11, 2015 at 09:41:47PM +0800, Peng Fan wrote:
> In drivers/mtd/mtd_blkdevs.c:
> 406	set_capacity(gd, (new->size * tr->blksize) >> 9);
> The type of new->size is unsigned long and the type of tr->blksize is int,
> the result of 'new->size * tr->blksize' may exceed ULONG_MAX on 32bit
> machines.
> 
> I use nand chip MT29F32G08CBADBWP which is 4GB and the parameters passed
> to kernel is 'mtdparts=gpmi-nand:-(user)', the whole nand chip will be
> treated as a 4GB mtd partition. new->size is 0x800000 and tr->blksize is
> 0x200, 'new->size * tr->blksize' however is 0. This is what we do not want
> to see.
> 
> Using type cast u64 to fix the multiplication overflow issue.
> 
> Signed-off-by: Peng Fan <van.freenix@...il.com>
> Cc: David Woodhouse <dwmw2@...radead.org>
> Cc: Brian Norris <computersforpeace@...il.com>
> ---
> 
> Changes V2:
>  use type cast to avoid build break for platforms which does not support 64 bit multilplication.

Thanks, pushed to l2-mtd.git
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