netfilter: nf_ct_helper: better logging for dropped packets

Connection tracking helpers have to drop packets under exceptional
situations. Currently, the user gets the following logging message
in case that happens:

	nf_ct_%s: dropping packet ...

However, depending on the helper, there are different reasons why a
packet can be dropped.

This patch modifies the existing code to provide more specific
error message in the scope of each helper to help users to debug
the reason why the packet has been dropped, ie:

	nf_ct_%s: dropping packet: reason ...

Thanks to Joe Perches for many formatting suggestions.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 53 insertions, 20 deletions

diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index 72a67bbe351..069229d919b 100644
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -1095,8 +1095,10 @@ static int process_sdp(struct sk_buff *skb, unsigned int protoff,
 		port = simple_strtoul(*dptr + mediaoff, NULL, 10);
 		if (port == 0)
 			continue;
-		if (port < 1024 || port > 65535)
+		if (port < 1024 || port > 65535) {
+			nf_ct_helper_log(skb, ct, "wrong port %u", port);
 			return NF_DROP;
+		}
 
 		/* The media description overrides the session description. */
 		maddr_len = 0;
@@ -1107,15 +1109,20 @@ static int process_sdp(struct sk_buff *skb, unsigned int protoff,
 			memcpy(&rtp_addr, &maddr, sizeof(rtp_addr));
 		} else if (caddr_len)
 			memcpy(&rtp_addr, &caddr, sizeof(rtp_addr));
-		else
+		else {
+			nf_ct_helper_log(skb, ct, "cannot parse SDP message");
 			return NF_DROP;
+		}
 
 		ret = set_expected_rtp_rtcp(skb, protoff, dataoff,
 					    dptr, datalen,
 					    &rtp_addr, htons(port), t->class,
 					    mediaoff, medialen);
-		if (ret != NF_ACCEPT)
+		if (ret != NF_ACCEPT) {
+			nf_ct_helper_log(skb, ct,
+					 "cannot add expectation for voice");
 			return ret;
+		}
 
 		/* Update media connection address if present */
 		if (maddr_len && nf_nat_sdp_addr && ct->status & IPS_NAT_MASK) {
@@ -1123,8 +1130,10 @@ static int process_sdp(struct sk_buff *skb, unsigned int protoff,
 					      dptr, datalen, mediaoff,
 					      SDP_HDR_CONNECTION, SDP_HDR_MEDIA,
 					      &rtp_addr);
-			if (ret != NF_ACCEPT)
+			if (ret != NF_ACCEPT) {
+				nf_ct_helper_log(skb, ct, "cannot mangle SDP");
 				return ret;
+			}
 		}
 		i++;
 	}
@@ -1258,9 +1267,10 @@ static int process_register_request(struct sk_buff *skb, unsigned int protoff,
 	ret = ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen,
 				      SIP_HDR_CONTACT, NULL,
 				      &matchoff, &matchlen, &daddr, &port);
-	if (ret < 0)
+	if (ret < 0) {
+		nf_ct_helper_log(skb, ct, "cannot parse contact");
 		return NF_DROP;
-	else if (ret == 0)
+	} else if (ret == 0)
 		return NF_ACCEPT;
 
 	/* We don't support third-party registrations */
@@ -1273,8 +1283,10 @@ static int process_register_request(struct sk_buff *skb, unsigned int protoff,
 
 	if (ct_sip_parse_numerical_param(ct, *dptr,
 					 matchoff + matchlen, *datalen,
-					 "expires=", NULL, NULL, &expires) < 0)
+					 "expires=", NULL, NULL, &expires) < 0) {
+		nf_ct_helper_log(skb, ct, "cannot parse expires");
 		return NF_DROP;
+	}
 
 	if (expires == 0) {
 		ret = NF_ACCEPT;
@@ -1282,8 +1294,10 @@ static int process_register_request(struct sk_buff *skb, unsigned int protoff,
 	}
 
 	exp = nf_ct_expect_alloc(ct);
-	if (!exp)
+	if (!exp) {
+		nf_ct_helper_log(skb, ct, "cannot alloc expectation");
 		return NF_DROP;
+	}
 
 	saddr = NULL;
 	if (sip_direct_signalling)
@@ -1300,9 +1314,10 @@ static int process_register_request(struct sk_buff *skb, unsigned int protoff,
 		ret = nf_nat_sip_expect(skb, protoff, dataoff, dptr, datalen,
 					exp, matchoff, matchlen);
 	else {
-		if (nf_ct_expect_related(exp) != 0)
+		if (nf_ct_expect_related(exp) != 0) {
+			nf_ct_helper_log(skb, ct, "cannot add expectation");
 			ret = NF_DROP;
-		else
+		} else
 			ret = NF_ACCEPT;
 	}
 	nf_ct_expect_put(exp);
@@ -1356,9 +1371,10 @@ static int process_register_response(struct sk_buff *skb, unsigned int protoff,
 					      SIP_HDR_CONTACT, &in_contact,
 					      &matchoff, &matchlen,
 					      &addr, &port);
-		if (ret < 0)
+		if (ret < 0) {
+			nf_ct_helper_log(skb, ct, "cannot parse contact");
 			return NF_DROP;
-		else if (ret == 0)
+		} else if (ret == 0)
 			break;
 
 		/* We don't support third-party registrations */
@@ -1373,8 +1389,10 @@ static int process_register_response(struct sk_buff *skb, unsigned int protoff,
 						   matchoff + matchlen,
 						   *datalen, "expires=",
 						   NULL, NULL, &c_expires);
-		if (ret < 0)
+		if (ret < 0) {
+			nf_ct_helper_log(skb, ct, "cannot parse expires");
 			return NF_DROP;
+		}
 		if (c_expires == 0)
 			break;
 		if (refresh_signalling_expectation(ct, &addr, proto, port,
@@ -1408,15 +1426,21 @@ static int process_sip_response(struct sk_buff *skb, unsigned int protoff,
 	if (*datalen < strlen("SIP/2.0 200"))
 		return NF_ACCEPT;
 	code = simple_strtoul(*dptr + strlen("SIP/2.0 "), NULL, 10);
-	if (!code)
+	if (!code) {
+		nf_ct_helper_log(skb, ct, "cannot get code");
 		return NF_DROP;
+	}
 
 	if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CSEQ,
-			      &matchoff, &matchlen) <= 0)
+			      &matchoff, &matchlen) <= 0) {
+		nf_ct_helper_log(skb, ct, "cannot parse cseq");
 		return NF_DROP;
+	}
 	cseq = simple_strtoul(*dptr + matchoff, NULL, 10);
-	if (!cseq)
+	if (!cseq) {
+		nf_ct_helper_log(skb, ct, "cannot get cseq");
 		return NF_DROP;
+	}
 	matchend = matchoff + matchlen + 1;
 
 	for (i = 0; i < ARRAY_SIZE(sip_handlers); i++) {
@@ -1471,11 +1495,15 @@ static int process_sip_request(struct sk_buff *skb, unsigned int protoff,
 			continue;
 
 		if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CSEQ,
-				      &matchoff, &matchlen) <= 0)
+				      &matchoff, &matchlen) <= 0) {
+			nf_ct_helper_log(skb, ct, "cannot parse cseq");
 			return NF_DROP;
+		}
 		cseq = simple_strtoul(*dptr + matchoff, NULL, 10);
-		if (!cseq)
+		if (!cseq) {
+			nf_ct_helper_log(skb, ct, "cannot get cseq");
 			return NF_DROP;
+		}
 
 		return handler->request(skb, protoff, dataoff, dptr, datalen,
 					cseq);
@@ -1498,8 +1526,10 @@ static int process_sip_msg(struct sk_buff *skb, struct nf_conn *ct,
 	if (ret == NF_ACCEPT && ct->status & IPS_NAT_MASK) {
 		nf_nat_sip = rcu_dereference(nf_nat_sip_hook);
 		if (nf_nat_sip && !nf_nat_sip(skb, protoff, dataoff,
-					      dptr, datalen))
+					      dptr, datalen)) {
+			nf_ct_helper_log(skb, ct, "cannot NAT SIP message");
 			ret = NF_DROP;
+		}
 	}
 
 	return ret;
@@ -1563,11 +1593,14 @@ static int sip_help_tcp(struct sk_buff *skb, unsigned int protoff,
 		end += strlen("\r\n\r\n") + clen;
 
 		msglen = origlen = end - dptr;
-		if (msglen > datalen)
+		if (msglen > datalen) {
+			nf_ct_helper_log(skb, ct, "incomplete/bad SIP message");
 			return NF_DROP;
+		}
 
 		ret = process_sip_msg(skb, ct, protoff, dataoff,
 				      &dptr, &msglen);
+		/* process_sip_* functions report why this packet is dropped */
 		if (ret != NF_ACCEPT)
 			break;
 		diff     = msglen - origlen;