linux-kernel - [PATCH v3 1/9] drm/mipi-dsi: Fix theoretical int overflow in mipi_dsi_dcs_write

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Date: Wed,  1 May 2024 08:41:04 -0700
From: Douglas Anderson <dianders@...omium.org>
To: dri-devel@...ts.freedesktop.org
Cc: Linus Walleij <linus.walleij@...aro.org>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Cong Yang <yangcong5@...qin.corp-partner.google.com>,
	Hsin-Yi Wang <hsinyi@...gle.com>,
	Brian Norris <briannorris@...omium.org>,
	Sam Ravnborg <sam@...nborg.org>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Javier Martinez Canillas <javierm@...hat.com>,
	Joel Selvaraj <jo@...amily.in>,
	lvzhaoxiong@...qin.corp-partner.google.com,
	Douglas Anderson <dianders@...omium.org>,
	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: [PATCH v3 1/9] drm/mipi-dsi: Fix theoretical int overflow in mipi_dsi_dcs_write_seq()

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 v3:
- Use %zd in print instead of casting errors to int.

Changes in v2:
- New

 include/drm/drm_mipi_dsi.h | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
index 82b1cc434ea3..70ce0b8cbc68 100644
--- a/include/drm/drm_mipi_dsi.h
+++ b/include/drm/drm_mipi_dsi.h
@@ -333,18 +333,18 @@ int mipi_dsi_dcs_get_display_brightness_large(struct mipi_dsi_device *dsi,
  * @cmd: Command
  * @seq: buffer containing data to be transmitted
  */
-#define mipi_dsi_dcs_write_seq(dsi, cmd, seq...)                           \
-	do {                                                               \
-		static const u8 d[] = { cmd, seq };                        \
-		struct device *dev = &dsi->dev;                            \
-		int 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);                                 \
-			return ret;                                        \
-		}                                                          \
+#define mipi_dsi_dcs_write_seq(dsi, cmd, seq...)                            \
+	do {                                                                \
+		static const u8 d[] = { cmd, seq };                         \
+		struct device *dev = &dsi->dev;                             \
+		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: %zd\n", \
+				cmd, ret);                                  \
+			return ret;                                         \
+		}                                                           \
 	} while (0)
 
 /**
-- 
2.45.0.rc0.197.gbae5840b3b-goog