[PATCH] i2c: mt7621: fix copying uninitialized kernel stack with reduced page_len

[Christian Marangi <ansuelsmth@gmail.com>]

When a page_len is less than 5 bytes in mtk_i2c_xfer, uninitialized kernel
stack data is copied and written to REG_SM0D1_REG. Equally on the read
part, an unnecessary read is done.

Guard these extra copy/write and read for the page_len to fix leaking
uninitialized stack memory.

Fixes: d04913ec5f89 ("i2c: mt7621: Add MediaTek MT7621/7628/7688 I2C driver")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
---
 drivers/i2c/busses/i2c-mt7621.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-mt7621.c b/drivers/i2c/busses/i2c-mt7621.c
index 19dde7c4069e..b4d2f9c5514d 100644
--- a/drivers/i2c/busses/i2c-mt7621.c
+++ b/drivers/i2c/busses/i2c-mt7621.c
@@ -96,7 +96,8 @@ static void mtk_i2c_reset(struct mtk_i2c *i2c)
 	 * configure open-drain mode, this bit needs to be cleared.
 	 */
 	reg = ((i2c->clk_div << 16) & SM0CTL0_CLK_DIV_MASK) | SM0CTL0_EN;
-	if (i2c->have_scl_stretch)
+	/* Set SCL_STRETCH only for Mediatek SoC */
+	if (device_is_compatible(i2c->dev, "mediatek,mt7621-i2c"))
 		reg |= SM0CTL0_SCL_STRETCH;
 
 	iowrite32(reg, i2c->base + REG_SM0CTL0_REG);
@@ -302,9 +303,8 @@ static int mtk_i2c_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	/* Set SCL_STRETCH only for Mediatek SoC */
 	if (device_is_compatible(i2c->dev, "mediatek,mt7621-i2c"))
-		i2c->have_scl_stretch = true;
+		i2c->have_scl_stretch
 
 	adap = &i2c->adap;
 	adap->owner = THIS_MODULE;
-- 
2.55.0