linux-kernel - Re: [PATCH v2 1/8] drm/mipi-dsi: Fix theoretical int overflow in mipi_dsi_dcs_write

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Date: Sat, 27 Apr 2024 08:22:02 +0200
From: Sam Ravnborg <sam@...nborg.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Douglas Anderson <dianders@...omium.org>
Cc: Douglas Anderson <dianders@...omium.org>,
	dri-devel@...ts.freedesktop.org,
	Linus Walleij <linus.walleij@...aro.org>,
	lvzhaoxiong@...qin.corp-partner.google.com,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Hsin-Yi Wang <hsinyi@...gle.com>,
	Javier Martinez Canillas <javierm@...hat.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Joel Selvaraj <jo@...amily.in>,
	Cong Yang <yangcong5@...qin.corp-partner.google.com>,
	Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...il.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/8] drm/mipi-dsi: Fix theoretical int overflow in
 mipi_dsi_dcs_write_seq()

On Sat, Apr 27, 2024 at 04:44:33AM +0300, Dmitry Baryshkov wrote:
> On Sat, 27 Apr 2024 at 02:59, Douglas Anderson <dianders@...omium.org> wrote:
> >
> > The mipi_dsi_dcs_write_seq() macro makes a call to
> > mipi_dsi_dcs_write_buffer() which returns a type ssize_t. The macro
> > then stores it in an int and checks to see if it's negative. This
> > could theoretically be a problem if "ssize_t" is larger than "int".
> >
> > To see the issue, imagine that "ssize_t" is 32-bits and "int" is
> > 16-bits, you could see a problem if there was some code out there that
> > looked like:
> >
> >   mipi_dsi_dcs_write_seq(dsi, cmd, <32767 bytes as arguments>);
> >
> > ...since we'd get back that 32768 bytes were transferred and 32768
> > stored in a 16-bit int would look negative.
> >
> > Though there are no callsites where we'd actually hit this (even if
> > "int" was only 16-bit), it's cleaner to make the types match so let's
> > fix it.
> >
> > Fixes: 2a9e9daf7523 ("drm/mipi-dsi: Introduce mipi_dsi_dcs_write_seq macro")
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > ---
> >
> > Changes in v2:
> > - New
> >
> >  include/drm/drm_mipi_dsi.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
> > index 82b1cc434ea3..b3576be22bfa 100644
> > --- a/include/drm/drm_mipi_dsi.h
> > +++ b/include/drm/drm_mipi_dsi.h
> > @@ -337,12 +337,12 @@ int mipi_dsi_dcs_get_display_brightness_large(struct mipi_dsi_device *dsi,
> >         do {                                                               \
> >                 static const u8 d[] = { cmd, seq };                        \
> >                 struct device *dev = &dsi->dev;                            \
> > -               int ret;                                                   \
> > +               ssize_t ret;                                               \
> >                 ret = mipi_dsi_dcs_write_buffer(dsi, d, ARRAY_SIZE(d));    \
> >                 if (ret < 0) {                                             \
> >                         dev_err_ratelimited(                               \
> >                                 dev, "sending command %#02x failed: %d\n", \
> > -                               cmd, ret);                                 \
> > +                               cmd, (int)ret);                            \
> 
> Please consider using %zd instead

Hi Douglas,
please consider the above for all the pathces, there are more places
where a cast can be dropped.

	Sam