[PATCH RESEND] 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 | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-mt7621.c b/drivers/i2c/busses/i2c-mt7621.c
index 0a288c998419..9ea5e3f9a763 100644
--- a/drivers/i2c/busses/i2c-mt7621.c
+++ b/drivers/i2c/busses/i2c-mt7621.c
@@ -144,7 +144,6 @@ static int mtk_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
 	u16 addr;
 	int i, j, ret, len, page_len;
 	u32 cmd;
-	u32 data[2];
 
 	i2c = i2c_get_adapdata(adap);
 
@@ -186,6 +185,8 @@ static int mtk_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
 
 		/* transfer data */
 		for (len = pmsg->len, j = 0; len > 0; len -= 8, j += 8) {
+			u32 data[2] = { };
+
 			page_len = (len >= 8) ? 8 : len;
 
 			if (pmsg->flags & I2C_M_RD) {
@@ -194,7 +195,8 @@ static int mtk_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
 			} else {
 				memcpy(data, &pmsg->buf[j], page_len);
 				iowrite32(data[0], i2c->base + REG_SM0D0_REG);
-				iowrite32(data[1], i2c->base + REG_SM0D1_REG);
+				if (page_len > 4)
+					iowrite32(data[1], i2c->base + REG_SM0D1_REG);
 				cmd = SM0CTL1_WRITE;
 			}
 
@@ -204,7 +206,8 @@ static int mtk_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
 
 			if (pmsg->flags & I2C_M_RD) {
 				data[0] = ioread32(i2c->base + REG_SM0D0_REG);
-				data[1] = ioread32(i2c->base + REG_SM0D1_REG);
+				if (page_len > 4)
+					data[1] = ioread32(i2c->base + REG_SM0D1_REG);
 				memcpy(&pmsg->buf[j], data, page_len);
 			} else {
 				if (!(pmsg->flags & I2C_M_IGNORE_NAK)) {
-- 
2.55.0