media: dvb-usb-v2: af9035: Fix null-ptr-deref in af9035_i2c_master_xfer

media: dvb-usb-v2: af9035: Fix null-ptr-deref in af9035_i2c_master_xfer

[ Upstream commit 7bf744f2de0a848fb1d717f5831b03db96feae89 ]

In af9035_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 af9035_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 0ed554fd769a
("media: dvb-usb: az6027: fix null-ptr-deref in az6027_i2c_xfer()")

Signed-off-by: Zhang Shurong <zhang_shurong@foxmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ moved variable declaration to fix build issues in older kernels - gregkh ]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>