media: af9035: prevent buffer overflow on write

BugLink: https://bugs.launchpad.net/bugs/1801900

[ Upstream commit 312f73b6 ]

When less than 3 bytes are written to the device, memcpy is called with
negative array size which leads to buffer overflow and kernel panic. This
patch adds a condition and returns -EOPNOTSUPP instead.
Fixes bugzilla issue 64871

[mchehab+samsung@kernel.org: fix a merge conflict and changed the
 condition to match the patch's comment, e. g. len == 3 could
 also be valid]
Signed-off-by: Jozef Balga <jozef.balga@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/media/usb/dvb-usb-v2/af9035.c

@@ -389,8 +389,10 @@ static int af9035_i2c_master_xfer(struct i2c_adapter *adap,
 			    msg[0].addr == (state->af9033_i2c_addr[1] >> 1))
 				reg |= 0x100000;
 
-			ret = af9035_wr_regs(d, reg, &msg[0].buf[3],
-					msg[0].len - 3);
+			ret = (msg[0].len >= 3) ? af9035_wr_regs(d, reg,
+							         &msg[0].buf[3],
+							         msg[0].len - 3)
+					        : -EOPNOTSUPP;
 		} else {
 			/* I2C write */
 			u8 buf[MAX_XFER_SIZE];