nat/bsc: Check proto before calling ipaccess_rcvmsg_base
The code in the BSC/NAT called ipaccess_rcvmsg_base without
checking if the protocol is IPA. This lead the BSC to respond
to SCCP messages with an "ID ACK". From a quick look neither
the code of ipaccess_rcvmsg_base in OpenBSC nor the copy of
libosmo-abis ever checked the protocol header. So this code
has been wrong since initially being created in 2010.
diff --git a/openbsc/src/osmo-bsc/osmo_bsc_msc.c b/openbsc/src/osmo-bsc/osmo_bsc_msc.c
index 04e9cf3..0acc290 100644
--- a/openbsc/src/osmo-bsc/osmo_bsc_msc.c
+++ b/openbsc/src/osmo-bsc/osmo_bsc_msc.c
@@ -270,11 +270,11 @@
/* handle base message handling */
hh = (struct ipaccess_head *) msg->data;
- ipaccess_rcvmsg_base(msg, bfd);
/* initialize the networking. This includes sending a GSM08.08 message */
msg->cb[0] = (unsigned long) data;
if (hh->proto == IPAC_PROTO_IPACCESS) {
+ ipaccess_rcvmsg_base(msg, bfd);
if (msg->l2h[0] == IPAC_MSGT_ID_ACK)
initialize_if_needed(data->msc_con);
else if (msg->l2h[0] == IPAC_MSGT_ID_GET) {