linux-kernel - Re: [PATCH] zram: Fix buffer size passed to strlcpy()

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Message-ID: <20170802235905.GI84665@google.com>
Date:   Wed, 2 Aug 2017 16:59:05 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Doug Anderson <dianders@...omium.org>,
        Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] zram: Fix buffer size passed to strlcpy()

El Thu, Aug 03, 2017 at 08:44:37AM +0900 Minchan Kim ha dit:

> Hi Doug,
> 
> On Wed, Aug 02, 2017 at 03:54:32PM -0700, Doug Anderson wrote:
> > Hi,
> > 
> > On Fri, Jul 28, 2017 at 10:12 AM, Matthias Kaehlcke <mka@...omium.org> wrote:
> > > comp_algorithm_store() passes the size of the source buffer to strlcpy()
> > > instead of the destination buffer size, fix this.
> > 
> > This was introduced in commit 415403be37e2 ("zram: use crypto api to
> > check alg availability"), but probably don't need a "Fixes" since
> > there's not really a bug (see below)
> > 
> > > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> > > ---
> > >  drivers/block/zram/zram_drv.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > > index 856d5dc02451..7d2ddffad361 100644
> > > --- a/drivers/block/zram/zram_drv.c
> > > +++ b/drivers/block/zram/zram_drv.c
> > > @@ -327,7 +327,7 @@ static ssize_t comp_algorithm_store(struct device *dev,
> > >                 return -EBUSY;
> > >         }
> > >
> > > -       strlcpy(zram->compressor, compressor, sizeof(compressor));
> > > +       strlcpy(zram->compressor, compressor, sizeof(zram->compressor));
> > 
> > As far as I can tell the two sizes are identical.  In struct zram:
> > 
> > char compressor[CRYPTO_MAX_ALG_NAME];
> > 
> > Locally here:
> > 
> > char compressor[CRYPTO_MAX_ALG_NAME];
> > 
> > ...so there is no bug per say unless there's a hidden "#undef".
> > ...but your change does make it a little clearer, plus if someone ever
> > changed one of these arrays it would be safer.  Thus:
> > 
> > Reviewed-by: Douglas Anderson <dianders@...omium.org>
> > 
> > 
> > I suppose another option would be to define the local array based on
> > the size of the structure.  AKA locally in the function:
> > 
> >   char compressor[ARRAY_SIZE(zram->compressor)];
> > 
> > ...if you did that you could replace the strlcpy() below with a simple
> > strcpy() since you'd be guaranteed that there's be enough space.
> > ...but I'm probably overthinking it too much. ;-P
> 
> First of all, Thanks for the patch, Matthias. You are correct and you
> patch doesn't have any problem. However, I think Doug's suggestion
> looks better. Could you mind resending?

Sure, I can rework the patch.