media: dvb-usb-v2: ce6230: fix null-ptr-deref in ce6230_i2c_master_xfer()

In ce6230_i2c_master_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 ce6230_i2c_master_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 0ed554fd ("media: dvb-usb: az6027: fix null-ptr-deref in az6027_i2c_xfer()")

Link: https://lore.kernel.org/linux-media/20230313092751.209496-1-harperchen1110@gmail.comSigned-off-by: Wei Chen <harperchen1110@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/usb/dvb-usb-v2/ce6230.c

@@ -101,6 +101,10 @@ static int ce6230_i2c_master_xfer(struct i2c_adapter *adap,
 		if (num > i + 1 && (msg[i+1].flags & I2C_M_RD)) {
 			if (msg[i].addr ==
 				ce6230_zl10353_config.demod_address) {
+				if (msg[i].len < 1) {
+					i = -EOPNOTSUPP;
+					break;
+				}
 				req.cmd = DEMOD_READ;
 				req.value = msg[i].addr >> 1;
 				req.index = msg[i].buf[0];
@@ -117,6 +121,10 @@ static int ce6230_i2c_master_xfer(struct i2c_adapter *adap,
 		} else {
 			if (msg[i].addr ==
 				ce6230_zl10353_config.demod_address) {
+				if (msg[i].len < 1) {
+					i = -EOPNOTSUPP;
+					break;
+				}
 				req.cmd = DEMOD_WRITE;
 				req.value = msg[i].addr >> 1;
 				req.index = msg[i].buf[0];