netfilter: nf_conntrack_sip: restrict RTP expect flushing on error to last request

Some Inovaphone PBXs exhibit very stange behaviour: when dialing for
example "123", the device sends INVITE requests for "1", "12" and
"123" back to back.  The first requests will elicit error responses
from the receiver, causing the SIP helper to flush the RTP
expectations even though we might still see a positive response.

Note the sequence number of the last INVITE request that contained a
media description and only flush the expectations when receiving a
negative response for that sequence number.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netfilter/nf_conntrack_sip.h

@@ -7,6 +7,7 @@
 
 struct nf_ct_sip_master {
 	unsigned int	register_cseq;
+	unsigned int	invite_cseq;
 };
 
 enum sip_expectation_classes {

net/netfilter/nf_conntrack_sip.c

@@ -870,6 +870,7 @@ static int process_sdp(struct sk_buff *skb,
 {
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
+	struct nf_conn_help *help = nfct_help(ct);
 	unsigned int matchoff, matchlen;
 	unsigned int mediaoff, medialen;
 	unsigned int sdpoff;
@@ -959,6 +960,9 @@ static int process_sdp(struct sk_buff *skb,
 	if (nf_nat_sdp_session && ct->status & IPS_NAT_MASK)
 		ret = nf_nat_sdp_session(skb, dptr, sdpoff, datalen, &rtp_addr);
 
+	if (ret == NF_ACCEPT && i > 0)
+		help->help.ct_sip_info.invite_cseq = cseq;
+
 	return ret;
 }
 static int process_invite_response(struct sk_buff *skb,
@@ -967,14 +971,14 @@ static int process_invite_response(struct sk_buff *skb,
 {
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
+	struct nf_conn_help *help = nfct_help(ct);
 
 	if ((code >= 100 && code <= 199) ||
 	    (code >= 200 && code <= 299))
 		return process_sdp(skb, dptr, datalen, cseq);
-	else {
+	else if (help->help.ct_sip_info.invite_cseq == cseq)
 		flush_expectations(ct, true);
-		return NF_ACCEPT;
-	}
+	return NF_ACCEPT;
 }
 
 static int process_update_response(struct sk_buff *skb,
@@ -983,14 +987,14 @@ static int process_update_response(struct sk_buff *skb,
 {
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
+	struct nf_conn_help *help = nfct_help(ct);
 
 	if ((code >= 100 && code <= 199) ||
 	    (code >= 200 && code <= 299))
 		return process_sdp(skb, dptr, datalen, cseq);
-	else {
+	else if (help->help.ct_sip_info.invite_cseq == cseq)
 		flush_expectations(ct, true);
-		return NF_ACCEPT;
-	}
+	return NF_ACCEPT;
 }
 
 static int process_prack_response(struct sk_buff *skb,
@@ -999,14 +1003,14 @@ static int process_prack_response(struct sk_buff *skb,
 {
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
+	struct nf_conn_help *help = nfct_help(ct);
 
 	if ((code >= 100 && code <= 199) ||
 	    (code >= 200 && code <= 299))
 		return process_sdp(skb, dptr, datalen, cseq);
-	else {
+	else if (help->help.ct_sip_info.invite_cseq == cseq)
 		flush_expectations(ct, true);
-		return NF_ACCEPT;
-	}
+	return NF_ACCEPT;
 }
 
 static int process_bye_request(struct sk_buff *skb,