[PATCH] media: imx274: fix stack corruption in imx274_read_reg

[Luca Ceresoli]

imx274_read_reg() takes a u8 pointer ("reg") and casts it to pass it
to regmap_read(), which takes an unsigned int pointer. This results in
a corrupted stack and random crashes.

Fixes: 0985dd306f72 ("media: imx274: V4l2 driver for Sony imx274 CMOS sensor")
Cc: stable@xxxxxxxxxxxxxxx # 4.15.x
Signed-off-by: Luca Ceresoli <luca@xxxxxxxxxxxxxxxx>

---

Notes!

I have no evidence of this bug showing up in the mainline driver. It
appeared on a modified version where imx274_read_reg() is used,
unmodified, in a different way than it does in mainline (passing a
pointer to a single u8 instead of a pointer to an element of a u8
array).

Also the bug is only present in versions v4.15 (where the driver was
added) to v4.19. The offending function is unused since commit
ca017467c78b ("media: imx274: add helper to read multibyte
registers"), merged in v4.20-rc1, thus master is not affected. I'm
sending this bugfix patch anyway for easier integration in the stable
branches. Later I plan to send a patch against master to entirely
remove the function. Or somebody might want to use this function
again, so better having a fixed version out anyway.

I'm not 100% sure this qualifies this commit for stable trees.
---
 drivers/media/i2c/imx274.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/media/i2c/imx274.c b/drivers/media/i2c/imx274.c
index e1b0395a657f..40c717f13eb8 100644
--- a/drivers/media/i2c/imx274.c
+++ b/drivers/media/i2c/imx274.c
@@ -619,16 +619,19 @@ static int imx274_write_table(struct stimx274 *priv, const struct reg_8 table[])
 
 static inline int imx274_read_reg(struct stimx274 *priv, u16 addr, u8 *val)
 {
+	unsigned int uint_val;
 	int err;
 
-	err = regmap_read(priv->regmap, addr, (unsigned int *)val);
+	err = regmap_read(priv->regmap, addr, &uint_val);
 	if (err)
 		dev_err(&priv->client->dev,
 			"%s : i2c read failed, addr = %x\n", __func__, addr);
 	else
 		dev_dbg(&priv->client->dev,
 			"%s : addr 0x%x, val=0x%x\n", __func__,
-			addr, *val);
+			addr, uint_val);
+
+	*val = uint_val;
 	return err;
 }
 
-- 
2.17.1