In dib7090p_rw_on_apb, msg is controlled by user. When msg[0].buf is null and
msg[0].len is zero, former checks on msg[0].buf would be passed. If accessing
msg[0].buf[2] without sanity check, null pointer deref would happen. We add
check on msg[0].len to prevent crash. Similar issue occurs when access
msg[1].buf[0] and msg[1].buf[1].

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

Signed-off-by: Alex Guo <alexguo1023@gmail.com>
---
 drivers/media/dvb-frontends/dib7000p.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/media/dvb-frontends/dib7000p.c b/drivers/media/dvb-frontends/dib7000p.c
index 46753d2ae212..9a309e23443a 100644
--- a/drivers/media/dvb-frontends/dib7000p.c
+++ b/drivers/media/dvb-frontends/dib7000p.c
@@ -2256,8 +2256,12 @@ static int dib7090p_rw_on_apb(struct i2c_adapter *i2c_adap,
 	u16 word;
 
 	if (num == 1) {		/* write */
+		if (msg[0].len < 3)
+			return -EOPNOTSUPP;
 		dib7000p_write_word(state, apb_address, ((msg[0].buf[1] << 8) | (msg[0].buf[2])));
 	} else {
+		if (msg[1].len < 2)
+			return -EOPNOTSUPP;
 		word = dib7000p_read_word(state, apb_address);
 		msg[1].buf[0] = (word >> 8) & 0xff;
 		msg[1].buf[1] = (word) & 0xff;
-- 
2.34.1