media: firewire: firedtv-avc: fix a buffer overflow in avc_ca_pmt()

The bounds checking in avc_ca_pmt() is not strict enough. It should
be checking "read_pos + 4" because it's reading 5 bytes. If the
"es_info_length" is non-zero then it reads a 6th byte so there needs to
be an additional check for that.

I also added checks for the "write_pos". I don't think these are
required because "read_pos" and "write_pos" are tied together so
checking one ought to be enough. But they make the code easier to
understand for me. The check on write_pos is:

if (write_pos + 4 >= sizeof(c->operand) - 4) {

The first "+ 4" is because we're writing 5 bytes and the last " - 4"
is to leave space for the CRC.

The other problem is that "length" can be invalid. It comes from
"data_length" in fdtv_ca_pmt().

Cc: [e-mail]
Reported-by: Luo Likang <[e-mail]>
Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/firewire/firedtv-avc.c

···
 		read_pos += program_info_length;
 		write_pos += program_info_length;
 	}
-	while (read_pos < length) {
+	while (read_pos + 4 < length) {
+		if (write_pos + 4 >= sizeof(c->operand) - 4) {
+			ret = -EINVAL;
+			goto out;
+		}
 		c->operand[write_pos++] = msg[read_pos++];
 		c->operand[write_pos++] = msg[read_pos++];
 		c->operand[write_pos++] = msg[read_pos++];
···
 		c->operand[write_pos++] = es_info_length >> 8;
 		c->operand[write_pos++] = es_info_length & 0xff;
 		if (es_info_length > 0) {
+			if (read_pos >= length) {
+				ret = -EINVAL;
+				goto out;
+			}
 			pmt_cmd_id = msg[read_pos++];
 			if (pmt_cmd_id != 1 && pmt_cmd_id != 4)
 				dev_err(fdtv->device, "invalid pmt_cmd_id %d at stream level\n",
 					pmt_cmd_id);
 
-			if (es_info_length > sizeof(c->operand) - 4 -
-					     write_pos) {
+			if (es_info_length > sizeof(c->operand) - 4 - write_pos ||
+			    es_info_length > length - read_pos) {
 				ret = -EINVAL;
 				goto out;
 			}

drivers/media/firewire/firedtv-ci.c

···
 	} else {
 		data_length = msg->msg[3];
 	}
+	if (data_length > sizeof(msg->msg) - data_pos)
+		return -EINVAL;
 
 	return avc_ca_pmt(fdtv, &msg->msg[data_pos], data_length);
 }