[media] si2157: Bounds check firmware

[ Upstream commit a828d72d ]

When reading the firmware and sending commands, the length
must be bounds checked to avoid overrunning the size of the command
buffer and smashing the stack if the firmware is not in the
expected format. Add the proper check.

Cc: stable@kernel.org
Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

drivers/media/tuners/si2157.c

@@ -157,6 +157,10 @@ static int si2157_init(struct dvb_frontend *fe)
 
 	for (remaining = fw->size; remaining > 0; remaining -= 17) {
 		len = fw->data[fw->size - remaining];
+		if (len > SI2157_ARGLEN) {
+			dev_err(&s->client->dev, "Bad firmware length\n");
+			goto err;
+		}
 		memcpy(cmd.args, &fw->data[(fw->size - remaining) + 1], len);
 		cmd.wlen = len;
 		cmd.rlen = 1;