media: dvb-usb-v2: rtl28xxu: fix null-ptr-deref in rtl28xxu_i2c_xfer

In rtl28xxu_i2c_xfer, msg is controlled by user. When msg[i].buf
is null and msg[i].len is zero, former checks on msg[i].buf would be
passed. Malicious data finally reach rtl28xxu_i2c_xfer. If accessing
msg[i].buf[0] without sanity check, null ptr deref would happen.
We add check on msg[i].len to prevent crash.

Similar commit:
commit 0ed554f
("media: dvb-usb: az6027: fix null-ptr-deref in az6027_i2c_xfer()")

Link: https://lore.kernel.org/linux-media/tencent_3623572106754AC2F266B316798B0F6CCA05@qq.com
Signed-off-by: Zhang Shurong <zhang_shurong@foxmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

Author: ZhangShurong

drivers/media/usb/dvb-usb-v2/rtl28xxu.c

@@ -176,6 +176,10 @@ static int rtl28xxu_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
 			ret = -EOPNOTSUPP;
 			goto err_mutex_unlock;
 		} else if (msg[0].addr == 0x10) {
+			if (msg[0].len < 1 || msg[1].len < 1) {
+				ret = -EOPNOTSUPP;
+				goto err_mutex_unlock;
+			}
 			/* method 1 - integrated demod */
 			if (msg[0].buf[0] == 0x00) {
 				/* return demod page from driver cache */
@@ -189,6 +193,10 @@ static int rtl28xxu_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
 				ret = rtl28xxu_ctrl_msg(d, &req);
 			}
 		} else if (msg[0].len < 2) {
+			if (msg[0].len < 1) {
+				ret = -EOPNOTSUPP;
+				goto err_mutex_unlock;
+			}
 			/* method 2 - old I2C */
 			req.value = (msg[0].buf[0] << 8) | (msg[0].addr << 1);
 			req.index = CMD_I2C_RD;
@@ -217,8 +225,16 @@ static int rtl28xxu_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
 			ret = -EOPNOTSUPP;
 			goto err_mutex_unlock;
 		} else if (msg[0].addr == 0x10) {
+			if (msg[0].len < 1) {
+				ret = -EOPNOTSUPP;
+				goto err_mutex_unlock;
+			}
 			/* method 1 - integrated demod */
 			if (msg[0].buf[0] == 0x00) {
+				if (msg[0].len < 2) {
+					ret = -EOPNOTSUPP;
+					goto err_mutex_unlock;
+				}
 				/* save demod page for later demod access */
 				dev->page = msg[0].buf[1];
 				ret = 0;
@@ -231,6 +247,10 @@ static int rtl28xxu_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
 				ret = rtl28xxu_ctrl_msg(d, &req);
 			}
 		} else if ((msg[0].len < 23) && (!dev->new_i2c_write)) {
+			if (msg[0].len < 1) {
+				ret = -EOPNOTSUPP;
+				goto err_mutex_unlock;
+			}
 			/* method 2 - old I2C */
 			req.value = (msg[0].buf[0] << 8) | (msg[0].addr << 1);
 			req.index = CMD_I2C_WR;