si2157: Bounds check firmware

commit a828d72d upstream.

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.
Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/media/tuners/si2157.c

@@ -165,6 +165,10 @@ 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(&client->dev, "Bad firmware length\n");
+			goto err_release_firmware;
+		}
 		memcpy(cmd.args, &fw->data[(fw->size - remaining) + 1], len);
 		cmd.wlen = len;
 		cmd.rlen = 1;