linux-kernel - Re: NAK: [PATCH][mtd-next] mtd: sharpslpart: fix overflow on block

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Date:   Wed, 08 Nov 2017 17:01:23 +0100
From:   Richard Weinberger <richard@....at>
To:     Colin Ian King <colin.king@...onical.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Andrea Adami <andrea.adami@...il.com>,
        linux-mtd@...ts.infradead.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: NAK: [PATCH][mtd-next] mtd: sharpslpart: fix overflow on block_adr calculation

Colin,

Am Mittwoch, 8. November 2017, 16:57:57 CET schrieb Colin Ian King:
> On 08/11/17 15:46, Colin King wrote:
> > From: Colin Ian King <colin.king@...onical.com>
> > 
> > Multiplying block_num and mtd->erasesize may potentially overflow
> > as they are both unsigned ints and so the multiplication is evaluated
> > in unsigned int arithmetic .  Cast block_adr to off_t to ensure
> > multiplication is off_t sized to avoid any potential overflow.
> > 
> > Detected by CoverityScan, CID#1461264 ("Unintentional integer overflow")
> > 
> > Fixes: fff1e32a50c0 ("mtd: sharpslpart: Add sharpslpart partition parser")
> > Signed-off-by: Colin Ian King <colin.king@...onical.com>
> > ---
> > 
> >  drivers/mtd/parsers/sharpslpart.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/mtd/parsers/sharpslpart.c
> > b/drivers/mtd/parsers/sharpslpart.c index 5fe0079ea5ed..b1d97aa3bac4
> > 100644
> > --- a/drivers/mtd/parsers/sharpslpart.c
> > +++ b/drivers/mtd/parsers/sharpslpart.c
> > @@ -244,7 +244,7 @@ static int sharpsl_nand_read_laddr(struct mtd_info
> > *mtd,> 
> >  		return -EINVAL;
> >  	
> >  	block_num = ftl->log2phy[log_num];
> > 
> > -	block_adr = block_num * mtd->erasesize;
> > +	block_adr = (loff_t)block_num * mtd->erasesize;
> > 
> >  	block_ofs = mtd_mod_by_eb((u32)from, mtd);
> >  	
> >  	err = mtd_read(mtd, block_adr + block_ofs, len, &retlen, buf);
> 
> Sorry, ignore this, there is another place that does this that needs
> some attention. I'll sent V2 shortly.

No need to hurry. :)
I agree that such overflows should be addressed, although they are purely 
theoretical. MTD is being used on small devices only.

Thanks,
//richard