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From: Krzysztof Kozlowski <krzk@kernel.org>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Colin King <colin.king@canonical.com>,
	Roger Quadros <rogerq@kernel.org>,
	Tony Lindgren <tony@atomide.com>,
	linux-omap@vger.kernel.org, kernel-janitors@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memory: gpmc: fix out of bounds read and dereference on gpmc_cs[]
Date: Wed, 24 Feb 2021 09:11:04 +0100	[thread overview]
Message-ID: <20210224081104.rw6amjl6p5so5cq7@kozik-lap> (raw)
In-Reply-To: <20210224075552.GS2087@kadam>

On Wed, Feb 24, 2021 at 10:55:52AM +0300, Dan Carpenter wrote:
> On Tue, Feb 23, 2021 at 07:38:21PM +0000, Colin King wrote:
> > From: Colin Ian King <colin.king@canonical.com>
> > 
> > Currently the array gpmc_cs is indexed by cs before it cs is range checked
> > and the pointer read from this out-of-index read is dereferenced. Fix this
> > by performing the range check on cs before the read and the following
> > pointer dereference.
> > 
> > Addresses-Coverity: ("Negative array index read")
> > Fixes: 186401937927 ("memory: gpmc: Move omap gpmc code to live under drivers")
> > Signed-off-by: Colin Ian King <colin.king@canonical.com>
> > ---
> >  drivers/memory/omap-gpmc.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/memory/omap-gpmc.c b/drivers/memory/omap-gpmc.c
> > index cfa730cfd145..f80c2ea39ca4 100644
> > --- a/drivers/memory/omap-gpmc.c
> > +++ b/drivers/memory/omap-gpmc.c
> > @@ -1009,8 +1009,8 @@ EXPORT_SYMBOL(gpmc_cs_request);
> >  
> >  void gpmc_cs_free(int cs)
> >  {
> > -	struct gpmc_cs_data *gpmc = &gpmc_cs[cs];
> > -	struct resource *res = &gpmc->mem;
> 
> There is no actual dereferencing going on here, it just taking the
> addresses.  But the patch is also harmless and improves readability.

Hm, in the second line indeed the compiler will just calculate the
offset of "mem" field against the "gpmc_cs+cs" and return it's probable
address.

To me still the code is a little bit non-obvious or obfuscated - first
you play with the array[index] and then you check the validity of index.

Best regards,
Krzysztof


  reply	other threads:[~2021-02-24  8:12 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-23 19:38 Colin King
2021-02-23 19:52 ` Krzysztof Kozlowski
2021-02-24  7:55 ` Dan Carpenter
2021-02-24  8:11   ` Krzysztof Kozlowski [this message]
2021-02-25 12:37     ` Tony Lindgren
2021-02-24  8:46   ` Colin Ian King
2021-03-02  8:44 ` Krzysztof Kozlowski
2021-03-02  8:54   ` Colin Ian King

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