V4L/DVB (11832): dibusb_mc: fix i2c to not corrupt eeprom in case of strange read pattern

dibusb_i2c_xfer seems to do things very dangerous :
it assumes that it get only write/read request or write request.

That means that read can be understood as write. For example a program
doing
file = open("/dev/i2c-x", O_RDWR);
    ioctl(file, I2C_SLAVE, 0x50)
read(file, data, 10)
    will corrupt the eeprom as it will be understood as a write.
Signed-off-by: NMatthieu CASTET <castet.matthieu@free.fr>
Signed-off-by: NPatrick Boettcher <pb@linuxtv.org>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/dvb/dvb-usb/dibusb-common.c

@@ -133,14 +133,17 @@ static int dibusb_i2c_xfer(struct i2c_adapter *adap,struct i2c_msg msg[],int num
 
 	for (i = 0; i < num; i++) {
 		/* write/read request */
-		if (i+1 < num && (msg[i+1].flags & I2C_M_RD)) {
+		if (i+1 < num && (msg[i].flags & I2C_M_RD) == 0
+					  && (msg[i+1].flags & I2C_M_RD)) {
 			if (dibusb_i2c_msg(d, msg[i].addr, msg[i].buf,msg[i].len,
 						msg[i+1].buf,msg[i+1].len) < 0)
 				break;
 			i++;
-		} else
+		} else if ((msg[i].flags & I2C_M_RD) == 0) {
 			if (dibusb_i2c_msg(d, msg[i].addr, msg[i].buf,msg[i].len,NULL,0) < 0)
 				break;
+		} else
+			break;
 	}
 
 	mutex_unlock(&d->i2c_mutex);