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

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Date:   Thu, 3 Aug 2017 08:44:37 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Matthias Kaehlcke <mka@...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()

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?

Thanks.