linux-kernel - Re: [PATCH] mmc: mmc_spi: fix snprintf() output buffer size

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Message-ID: <CAPDyKFpNuKMQhqiWhOz2j+9Ubj_FaBb54x-GincD6m2n6UbH0Q@mail.gmail.com>
Date: Tue, 8 Oct 2024 16:16:24 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Christophe JAILLET <christophe.jaillet@...adoo.fr>, linux-mmc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH] mmc: mmc_spi: fix snprintf() output buffer size

On Tue, 8 Oct 2024 at 09:13, Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> On Mon, Oct 7, 2024 at 8:09 PM Christophe JAILLET
> <christophe.jaillet@...adoo.fr> wrote:
> >
> > Le 07/10/2024 à 13:45, Bartosz Golaszewski a écrit :
> > > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > >
> > > GCC 13 complains about the truncated output of snprintf():
> > >
> > > drivers/mmc/host/mmc_spi.c: In function ‘mmc_spi_response_get’:
> > > drivers/mmc/host/mmc_spi.c:227:64: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
> > >    227 |         snprintf(tag, sizeof(tag), "  ... CMD%d response SPI_%s",
> > >        |                                                                ^
> > > drivers/mmc/host/mmc_spi.c:227:9: note: ‘snprintf’ output between 26 and 43 bytes into a destination of size 32
> > >    227 |         snprintf(tag, sizeof(tag), "  ... CMD%d response SPI_%s",
> > >        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >    228 |                 cmd->opcode, maptype(cmd));
> > >
> > > Increase the size of the target buffer.
> > >
> > > Fixes: 15a0580ced08 ("mmc_spi host driver")
> > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > > ---
> > >   drivers/mmc/host/mmc_spi.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
> > > index 8fee7052f2ef..fa1d1a1b3142 100644
> > > --- a/drivers/mmc/host/mmc_spi.c
> > > +++ b/drivers/mmc/host/mmc_spi.c
> > > @@ -222,7 +222,7 @@ static int mmc_spi_response_get(struct mmc_spi_host *host,
> > >       u8      leftover = 0;
> > >       unsigned short rotator;
> > >       int     i;
> > > -     char    tag[32];
> > > +     char    tag[43];
> > >
> > >       snprintf(tag, sizeof(tag), "  ... CMD%d response SPI_%s",
> > >               cmd->opcode, maptype(cmd));
> >
> > 'tag' is only used in a dev_dbg() at the end of the function.
> >
> > Maybe "  ... CMD%d response SPI_%s" could me moved directly within the
> > dev_dbg(). This would save a few bytes on the stack, save a snprintf()
> > in the normal path and fix the warning without the need of magic number.
> >
> > just my 2c.
> >
> > CJ
>
> I would be hesitant to change this logic here. The cmd struct is
> manipulated pretty extensively later in the function which leads me to
> believe that this snprintf() here was done on purpose.

The cmd->opcode and cmd->flags aren't really something a host driver
should need to change. It's the core that sets them to inform the host
driver about the command.

I looked closer and it seems to be correct in this case too.

Kind regards
Uffe