media: dvb-usb: digitv: fix null-ptr-deref in digitv_i2c_xfer()

In digitv_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 digitv_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 0ed554fd769a ("media: dvb-usb: az6027: fix null-ptr-deref in az6027_i2c_xfer()")

Link: https://lore.kernel.org/linux-media/20230313095008.1039689-1-harperchen1110@gmail.com
Signed-off-by: Wei Chen <harperchen1110@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

diff --git a/drivers/media/usb/dvb-usb/digitv.c b/drivers/media/usb/dvb-usb/digitv.c
index 2756815a780bca7e2c2fc07f549d0c3ca99651a4..32134be1691489fa3bed90cc97f68f8eea8179a0 100644 (file)
--- a/drivers/media/usb/dvb-usb/digitv.c
+++ b/drivers/media/usb/dvb-usb/digitv.c
@@ -63,6 +63,10 @@ static int digitv_i2c_xfer(struct i2c_adapter *adap,struct i2c_msg msg[],int num
                warn("more than 2 i2c messages at a time is not handled yet. TODO.");
 
        for (i = 0; i < num; i++) {
+               if (msg[i].len < 1) {
+                       i = -EOPNOTSUPP;
+                       break;
+               }
                /* write/read request */
                if (i+1 < num && (msg[i+1].flags & I2C_M_RD)) {
                        if (digitv_ctrl_msg(d, USB_READ_COFDM, msg[i].buf[0], NULL, 0,