linux-kernel - [PATCH v2 2/2] drm/bridge: ti-sn65dsi86: Never store more than msg->size bytes in AUX xfer

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Message-ID: <20231214123205.v2.2.I7b83c0f31aeedc6b1dc98c7c741d3e1f94f040f8@changeid>
Date: Thu, 14 Dec 2023 12:32:06 -0800
From: Douglas Anderson <dianders@...omium.org>
To: dri-devel@...ts.freedesktop.org
Cc: Guenter Roeck <groeck@...omium.org>,
	Douglas Anderson <dianders@...omium.org>,
	Andrzej Hajda <andrzej.hajda@...el.com>,
	Daniel Vetter <daniel@...ll.ch>,
	David Airlie <airlied@...il.com>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Jonas Karlman <jonas@...boo.se>,
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Robert Foss <rfoss@...nel.org>,
	Sam Ravnborg <sam@...nborg.org>,
	Stephen Boyd <swboyd@...omium.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] drm/bridge: ti-sn65dsi86: Never store more than msg->size bytes in AUX xfer

For aux reads, the value `msg->size` indicates the size of the buffer
provided by `msg->buffer`. We should never in any circumstances write
more bytes to the buffer since it may overflow the buffer.

In the ti-sn65dsi86 driver there is one code path that reads the
transfer length from hardware. Even though it's never been seen to be
a problem, we should make extra sure that the hardware isn't
increasing the length since doing so would cause us to overrun the
buffer.

Fixes: 982f589bde7a ("drm/bridge: ti-sn65dsi86: Update reply on aux failures")
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---

Changes in v2:
- Updated patch subject to match ps8640 patch.

 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 9095d1453710..62cc3893dca5 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -527,6 +527,7 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
 	u32 request_val = AUX_CMD_REQ(msg->request);
 	u8 *buf = msg->buffer;
 	unsigned int len = msg->size;
+	unsigned int short_len;
 	unsigned int val;
 	int ret;
 	u8 addr_len[SN_AUX_LENGTH_REG + 1 - SN_AUX_ADDR_19_16_REG];
@@ -600,7 +601,8 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
 	}
 
 	if (val & AUX_IRQ_STATUS_AUX_SHORT) {
-		ret = regmap_read(pdata->regmap, SN_AUX_LENGTH_REG, &len);
+		ret = regmap_read(pdata->regmap, SN_AUX_LENGTH_REG, &short_len);
+		len = min(len, short_len);
 		if (ret)
 			goto exit;
 	} else if (val & AUX_IRQ_STATUS_NAT_I2C_FAIL) {
-- 
2.43.0.472.g3155946c3a-goog