netfilter: nf_conntrack_sip: pass data offset to NAT functions

When using TCP multiple SIP messages might be present in a single packet.
A following patch will parse them by setting the dptr to the beginning of
each message. The NAT helper needs to reload the dptr value after mangling
the packet however, so it needs to know the offset of the message to the
beginning of the packet.

Signed-off-by: Patrick McHardy <kaber@trash.net>

include/linux/netfilter/nf_conntrack_sip.h

@@ -34,10 +34,10 @@ struct sdp_media_type {
 struct sip_handler {
 	const char	*method;
 	unsigned int	len;
-	int		(*request)(struct sk_buff *skb,
+	int		(*request)(struct sk_buff *skb, unsigned int dataoff,
 				   const char **dptr, unsigned int *datalen,
 				   unsigned int cseq);
-	int		(*response)(struct sk_buff *skb,
+	int		(*response)(struct sk_buff *skb, unsigned int dataoff,
 				    const char **dptr, unsigned int *datalen,
 				    unsigned int cseq, unsigned int code);
 };
@@ -100,33 +100,39 @@ enum sdp_header_types {
 };
 
 extern unsigned int (*nf_nat_sip_hook)(struct sk_buff *skb,
+				       unsigned int dataoff,
 				       const char **dptr,
 				       unsigned int *datalen);
 extern unsigned int (*nf_nat_sip_expect_hook)(struct sk_buff *skb,
+					      unsigned int dataoff,
 					      const char **dptr,
 					      unsigned int *datalen,
 					      struct nf_conntrack_expect *exp,
 					      unsigned int matchoff,
 					      unsigned int matchlen);
 extern unsigned int (*nf_nat_sdp_addr_hook)(struct sk_buff *skb,
-					    const char **dptr,
 					    unsigned int dataoff,
+					    const char **dptr,
 					    unsigned int *datalen,
+					    unsigned int sdpoff,
 					    enum sdp_header_types type,
 					    enum sdp_header_types term,
 					    const union nf_inet_addr *addr);
 extern unsigned int (*nf_nat_sdp_port_hook)(struct sk_buff *skb,
+					    unsigned int dataoff,
 					    const char **dptr,
 					    unsigned int *datalen,
 					    unsigned int matchoff,
 					    unsigned int matchlen,
 					    u_int16_t port);
 extern unsigned int (*nf_nat_sdp_session_hook)(struct sk_buff *skb,
-					       const char **dptr,
 					       unsigned int dataoff,
+					       const char **dptr,
 					       unsigned int *datalen,
+					       unsigned int sdpoff,
 					       const union nf_inet_addr *addr);
 extern unsigned int (*nf_nat_sdp_media_hook)(struct sk_buff *skb,
+					     unsigned int dataoff,
 					     const char **dptr,
 					     unsigned int *datalen,
 					     struct nf_conntrack_expect *rtp_exp,

net/ipv4/netfilter/nf_nat_sip.c

@@ -29,7 +29,7 @@ MODULE_DESCRIPTION("SIP NAT helper");
 MODULE_ALIAS("ip_nat_sip");
 
 
-static unsigned int mangle_packet(struct sk_buff *skb,
+static unsigned int mangle_packet(struct sk_buff *skb, unsigned int dataoff,
 				  const char **dptr, unsigned int *datalen,
 				  unsigned int matchoff, unsigned int matchlen,
 				  const char *buffer, unsigned int buflen)
@@ -42,12 +42,12 @@ static unsigned int mangle_packet(struct sk_buff *skb,
 		return 0;
 
 	/* Reload data pointer and adjust datalen value */
-	*dptr = skb->data + ip_hdrlen(skb) + sizeof(struct udphdr);
+	*dptr = skb->data + dataoff;
 	*datalen += buflen - matchlen;
 	return 1;
 }
 
-static int map_addr(struct sk_buff *skb,
+static int map_addr(struct sk_buff *skb, unsigned int dataoff,
 		    const char **dptr, unsigned int *datalen,
 		    unsigned int matchoff, unsigned int matchlen,
 		    union nf_inet_addr *addr, __be16 port)
@@ -76,11 +76,11 @@ static int map_addr(struct sk_buff *skb,
 
 	buflen = sprintf(buffer, "%pI4:%u", &newaddr, ntohs(newport));
 
-	return mangle_packet(skb, dptr, datalen, matchoff, matchlen,
+	return mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
 			     buffer, buflen);
 }
 
-static int map_sip_addr(struct sk_buff *skb,
+static int map_sip_addr(struct sk_buff *skb, unsigned int dataoff,
 			const char **dptr, unsigned int *datalen,
 			enum sip_header_types type)
 {
@@ -93,16 +93,17 @@ static int map_sip_addr(struct sk_buff *skb,
 	if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen, type, NULL,
 				    &matchoff, &matchlen, &addr, &port) <= 0)
 		return 1;
-	return map_addr(skb, dptr, datalen, matchoff, matchlen, &addr, port);
+	return map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
+			&addr, port);
 }
 
-static unsigned int ip_nat_sip(struct sk_buff *skb,
+static unsigned int ip_nat_sip(struct sk_buff *skb, unsigned int dataoff,
 			       const char **dptr, unsigned int *datalen)
 {
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
-	unsigned int dataoff, matchoff, matchlen;
+	unsigned int coff, matchoff, matchlen;
 	union nf_inet_addr addr;
 	__be16 port;
 	int request, in_header;
@@ -112,7 +113,7 @@ static unsigned int ip_nat_sip(struct sk_buff *skb,
 		if (ct_sip_parse_request(ct, *dptr, *datalen,
 					 &matchoff, &matchlen,
 					 &addr, &port) > 0 &&
-		    !map_addr(skb, dptr, datalen, matchoff, matchlen,
+		    !map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
 			      &addr, port))
 			return NF_DROP;
 		request = 1;
@@ -138,7 +139,7 @@ static unsigned int ip_nat_sip(struct sk_buff *skb,
 				goto next;
 		}
 
-		if (!map_addr(skb, dptr, datalen, matchoff, matchlen,
+		if (!map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
 			      &addr, port))
 			return NF_DROP;
 
@@ -153,8 +154,8 @@ static unsigned int ip_nat_sip(struct sk_buff *skb,
 		    addr.ip != ct->tuplehash[!dir].tuple.dst.u3.ip) {
 			buflen = sprintf(buffer, "%pI4",
 					&ct->tuplehash[!dir].tuple.dst.u3.ip);
-			if (!mangle_packet(skb, dptr, datalen, poff, plen,
-					   buffer, buflen))
+			if (!mangle_packet(skb, dataoff, dptr, datalen,
+					   poff, plen, buffer, buflen))
 				return NF_DROP;
 		}
 
@@ -167,8 +168,8 @@ static unsigned int ip_nat_sip(struct sk_buff *skb,
 		    addr.ip != ct->tuplehash[!dir].tuple.src.u3.ip) {
 			buflen = sprintf(buffer, "%pI4",
 					&ct->tuplehash[!dir].tuple.src.u3.ip);
-			if (!mangle_packet(skb, dptr, datalen, poff, plen,
-					   buffer, buflen))
+			if (!mangle_packet(skb, dataoff, dptr, datalen,
+					   poff, plen, buffer, buflen))
 				return NF_DROP;
 		}
 
@@ -181,27 +182,27 @@ static unsigned int ip_nat_sip(struct sk_buff *skb,
 		    htons(n) != ct->tuplehash[!dir].tuple.src.u.udp.port) {
 			__be16 p = ct->tuplehash[!dir].tuple.src.u.udp.port;
 			buflen = sprintf(buffer, "%u", ntohs(p));
-			if (!mangle_packet(skb, dptr, datalen, poff, plen,
-					   buffer, buflen))
+			if (!mangle_packet(skb, dataoff, dptr, datalen,
+					   poff, plen, buffer, buflen))
 				return NF_DROP;
 		}
 	}
 
 next:
 	/* Translate Contact headers */
-	dataoff = 0;
+	coff = 0;
 	in_header = 0;
-	while (ct_sip_parse_header_uri(ct, *dptr, &dataoff, *datalen,
+	while (ct_sip_parse_header_uri(ct, *dptr, &coff, *datalen,
 				       SIP_HDR_CONTACT, &in_header,
 				       &matchoff, &matchlen,
 				       &addr, &port) > 0) {
-		if (!map_addr(skb, dptr, datalen, matchoff, matchlen,
+		if (!map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
 			      &addr, port))
 			return NF_DROP;
 	}
 
-	if (!map_sip_addr(skb, dptr, datalen, SIP_HDR_FROM) ||
-	    !map_sip_addr(skb, dptr, datalen, SIP_HDR_TO))
+	if (!map_sip_addr(skb, dataoff, dptr, datalen, SIP_HDR_FROM) ||
+	    !map_sip_addr(skb, dataoff, dptr, datalen, SIP_HDR_TO))
 		return NF_DROP;
 	return NF_ACCEPT;
 }
@@ -232,7 +233,7 @@ static void ip_nat_sip_expected(struct nf_conn *ct,
 	}
 }
 
-static unsigned int ip_nat_sip_expect(struct sk_buff *skb,
+static unsigned int ip_nat_sip_expect(struct sk_buff *skb, unsigned int dataoff,
 				      const char **dptr, unsigned int *datalen,
 				      struct nf_conntrack_expect *exp,
 				      unsigned int matchoff,
@@ -279,8 +280,8 @@ static unsigned int ip_nat_sip_expect(struct sk_buff *skb,
 	if (exp->tuple.dst.u3.ip != exp->saved_ip ||
 	    exp->tuple.dst.u.udp.port != exp->saved_proto.udp.port) {
 		buflen = sprintf(buffer, "%pI4:%u", &newip, port);
-		if (!mangle_packet(skb, dptr, datalen, matchoff, matchlen,
-				   buffer, buflen))
+		if (!mangle_packet(skb, dataoff, dptr, datalen,
+				   matchoff, matchlen, buffer, buflen))
 			goto err;
 	}
 	return NF_ACCEPT;
@@ -290,7 +291,7 @@ err:
 	return NF_DROP;
 }
 
-static int mangle_content_len(struct sk_buff *skb,
+static int mangle_content_len(struct sk_buff *skb, unsigned int dataoff,
 			      const char **dptr, unsigned int *datalen)
 {
 	enum ip_conntrack_info ctinfo;
@@ -312,12 +313,13 @@ static int mangle_content_len(struct sk_buff *skb,
 		return 0;
 
 	buflen = sprintf(buffer, "%u", c_len);
-	return mangle_packet(skb, dptr, datalen, matchoff, matchlen,
+	return mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
 			     buffer, buflen);
 }
 
-static int mangle_sdp_packet(struct sk_buff *skb, const char **dptr,
-			     unsigned int dataoff, unsigned int *datalen,
+static int mangle_sdp_packet(struct sk_buff *skb, unsigned int dataoff,
+			     const char **dptr, unsigned int *datalen,
+			     unsigned int sdpoff,
 			     enum sdp_header_types type,
 			     enum sdp_header_types term,
 			     char *buffer, int buflen)
@@ -326,16 +328,16 @@ static int mangle_sdp_packet(struct sk_buff *skb, const char **dptr,
 	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 	unsigned int matchlen, matchoff;
 
-	if (ct_sip_get_sdp_header(ct, *dptr, dataoff, *datalen, type, term,
+	if (ct_sip_get_sdp_header(ct, *dptr, sdpoff, *datalen, type, term,
 				  &matchoff, &matchlen) <= 0)
 		return -ENOENT;
-	return mangle_packet(skb, dptr, datalen, matchoff, matchlen,
+	return mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
 			     buffer, buflen) ? 0 : -EINVAL;
 }
 
-static unsigned int ip_nat_sdp_addr(struct sk_buff *skb, const char **dptr,
-				    unsigned int dataoff,
-				    unsigned int *datalen,
+static unsigned int ip_nat_sdp_addr(struct sk_buff *skb, unsigned int dataoff,
+				    const char **dptr, unsigned int *datalen,
+				    unsigned int sdpoff,
 				    enum sdp_header_types type,
 				    enum sdp_header_types term,
 				    const union nf_inet_addr *addr)
@@ -344,16 +346,15 @@ static unsigned int ip_nat_sdp_addr(struct sk_buff *skb, const char **dptr,
 	unsigned int buflen;
 
 	buflen = sprintf(buffer, "%pI4", &addr->ip);
-	if (mangle_sdp_packet(skb, dptr, dataoff, datalen, type, term,
+	if (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff, type, term,
 			      buffer, buflen))
 		return 0;
 
-	return mangle_content_len(skb, dptr, datalen);
+	return mangle_content_len(skb, dataoff, dptr, datalen);
 }
 
-static unsigned int ip_nat_sdp_port(struct sk_buff *skb,
-				    const char **dptr,
-				    unsigned int *datalen,
+static unsigned int ip_nat_sdp_port(struct sk_buff *skb, unsigned int dataoff,
+				    const char **dptr, unsigned int *datalen,
 				    unsigned int matchoff,
 				    unsigned int matchlen,
 				    u_int16_t port)
@@ -362,16 +363,16 @@ static unsigned int ip_nat_sdp_port(struct sk_buff *skb,
 	unsigned int buflen;
 
 	buflen = sprintf(buffer, "%u", port);
-	if (!mangle_packet(skb, dptr, datalen, matchoff, matchlen,
+	if (!mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
 			   buffer, buflen))
 		return 0;
 
-	return mangle_content_len(skb, dptr, datalen);
+	return mangle_content_len(skb, dataoff, dptr, datalen);
 }
 
-static unsigned int ip_nat_sdp_session(struct sk_buff *skb, const char **dptr,
-				       unsigned int dataoff,
-				       unsigned int *datalen,
+static unsigned int ip_nat_sdp_session(struct sk_buff *skb, unsigned int dataoff,
+				       const char **dptr, unsigned int *datalen,
+				       unsigned int sdpoff,
 				       const union nf_inet_addr *addr)
 {
 	char buffer[sizeof("nnn.nnn.nnn.nnn")];
@@ -379,12 +380,12 @@ static unsigned int ip_nat_sdp_session(struct sk_buff *skb, const char **dptr,
 
 	/* Mangle session description owner and contact addresses */
 	buflen = sprintf(buffer, "%pI4", &addr->ip);
-	if (mangle_sdp_packet(skb, dptr, dataoff, datalen,
+	if (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff,
 			       SDP_HDR_OWNER_IP4, SDP_HDR_MEDIA,
 			       buffer, buflen))
 		return 0;
 
-	switch (mangle_sdp_packet(skb, dptr, dataoff, datalen,
+	switch (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff,
 				  SDP_HDR_CONNECTION_IP4, SDP_HDR_MEDIA,
 				  buffer, buflen)) {
 	case 0:
@@ -401,14 +402,13 @@ static unsigned int ip_nat_sdp_session(struct sk_buff *skb, const char **dptr,
 		return 0;
 	}
 
-	return mangle_content_len(skb, dptr, datalen);
+	return mangle_content_len(skb, dataoff, dptr, datalen);
 }
 
 /* So, this packet has hit the connection tracking matching code.
    Mangle it, and change the expectation to match the new version. */
-static unsigned int ip_nat_sdp_media(struct sk_buff *skb,
-				     const char **dptr,
-				     unsigned int *datalen,
+static unsigned int ip_nat_sdp_media(struct sk_buff *skb, unsigned int dataoff,
+				     const char **dptr, unsigned int *datalen,
 				     struct nf_conntrack_expect *rtp_exp,
 				     struct nf_conntrack_expect *rtcp_exp,
 				     unsigned int mediaoff,
@@ -456,7 +456,8 @@ static unsigned int ip_nat_sdp_media(struct sk_buff *skb,
 
 	/* Update media port. */
 	if (rtp_exp->tuple.dst.u.udp.port != rtp_exp->saved_proto.udp.port &&
-	    !ip_nat_sdp_port(skb, dptr, datalen, mediaoff, medialen, port))
+	    !ip_nat_sdp_port(skb, dataoff, dptr, datalen,
+			     mediaoff, medialen, port))
 		goto err2;
 
 	return NF_ACCEPT;

net/netfilter/nf_conntrack_sip.c

@@ -50,12 +50,13 @@ module_param(sip_direct_media, int, 0600);
 MODULE_PARM_DESC(sip_direct_media, "Expect Media streams between signalling "
 				   "endpoints only (default 1)");
 
-unsigned int (*nf_nat_sip_hook)(struct sk_buff *skb,
+unsigned int (*nf_nat_sip_hook)(struct sk_buff *skb, unsigned int dataoff,
 				const char **dptr,
 				unsigned int *datalen) __read_mostly;
 EXPORT_SYMBOL_GPL(nf_nat_sip_hook);
 
 unsigned int (*nf_nat_sip_expect_hook)(struct sk_buff *skb,
+				       unsigned int dataoff,
 				       const char **dptr,
 				       unsigned int *datalen,
 				       struct nf_conntrack_expect *exp,
@@ -63,17 +64,17 @@ unsigned int (*nf_nat_sip_expect_hook)(struct sk_buff *skb,
 				       unsigned int matchlen) __read_mostly;
 EXPORT_SYMBOL_GPL(nf_nat_sip_expect_hook);
 
-unsigned int (*nf_nat_sdp_addr_hook)(struct sk_buff *skb,
+unsigned int (*nf_nat_sdp_addr_hook)(struct sk_buff *skb, unsigned int dataoff,
 				     const char **dptr,
-				     unsigned int dataoff,
 				     unsigned int *datalen,
+				     unsigned int sdpoff,
 				     enum sdp_header_types type,
 				     enum sdp_header_types term,
 				     const union nf_inet_addr *addr)
 				     __read_mostly;
 EXPORT_SYMBOL_GPL(nf_nat_sdp_addr_hook);
 
-unsigned int (*nf_nat_sdp_port_hook)(struct sk_buff *skb,
+unsigned int (*nf_nat_sdp_port_hook)(struct sk_buff *skb, unsigned int dataoff,
 				     const char **dptr,
 				     unsigned int *datalen,
 				     unsigned int matchoff,
@@ -82,14 +83,15 @@ unsigned int (*nf_nat_sdp_port_hook)(struct sk_buff *skb,
 EXPORT_SYMBOL_GPL(nf_nat_sdp_port_hook);
 
 unsigned int (*nf_nat_sdp_session_hook)(struct sk_buff *skb,
-					const char **dptr,
 					unsigned int dataoff,
+					const char **dptr,
 					unsigned int *datalen,
+					unsigned int sdpoff,
 					const union nf_inet_addr *addr)
 					__read_mostly;
 EXPORT_SYMBOL_GPL(nf_nat_sdp_session_hook);
 
-unsigned int (*nf_nat_sdp_media_hook)(struct sk_buff *skb,
+unsigned int (*nf_nat_sdp_media_hook)(struct sk_buff *skb, unsigned int dataoff,
 				      const char **dptr,
 				      unsigned int *datalen,
 				      struct nf_conntrack_expect *rtp_exp,
@@ -729,7 +731,7 @@ static void flush_expectations(struct nf_conn *ct, bool media)
 	spin_unlock_bh(&nf_conntrack_lock);
 }
 
-static int set_expected_rtp_rtcp(struct sk_buff *skb,
+static int set_expected_rtp_rtcp(struct sk_buff *skb, unsigned int dataoff,
 				 const char **dptr, unsigned int *datalen,
 				 union nf_inet_addr *daddr, __be16 port,
 				 enum sip_expectation_classes class,
@@ -806,7 +808,7 @@ static int set_expected_rtp_rtcp(struct sk_buff *skb,
 	if (direct_rtp) {
 		nf_nat_sdp_port = rcu_dereference(nf_nat_sdp_port_hook);
 		if (nf_nat_sdp_port &&
-		    !nf_nat_sdp_port(skb, dptr, datalen,
+		    !nf_nat_sdp_port(skb, dataoff, dptr, datalen,
 				     mediaoff, medialen, ntohs(rtp_port)))
 			goto err1;
 	}
@@ -828,7 +830,8 @@ static int set_expected_rtp_rtcp(struct sk_buff *skb,
 
 	nf_nat_sdp_media = rcu_dereference(nf_nat_sdp_media_hook);
 	if (nf_nat_sdp_media && ct->status & IPS_NAT_MASK && !direct_rtp)
-		ret = nf_nat_sdp_media(skb, dptr, datalen, rtp_exp, rtcp_exp,
+		ret = nf_nat_sdp_media(skb, dataoff, dptr, datalen,
+				       rtp_exp, rtcp_exp,
 				       mediaoff, medialen, daddr);
 	else {
 		if (nf_ct_expect_related(rtp_exp) == 0) {
@@ -867,7 +870,7 @@ static const struct sdp_media_type *sdp_media_type(const char *dptr,
 	return NULL;
 }
 
-static int process_sdp(struct sk_buff *skb,
+static int process_sdp(struct sk_buff *skb, unsigned int dataoff,
 		       const char **dptr, unsigned int *datalen,
 		       unsigned int cseq)
 {
@@ -942,7 +945,7 @@ static int process_sdp(struct sk_buff *skb,
 		else
 			return NF_DROP;
 
-		ret = set_expected_rtp_rtcp(skb, dptr, datalen,
+		ret = set_expected_rtp_rtcp(skb, dataoff, dptr, datalen,
 					    &rtp_addr, htons(port), t->class,
 					    mediaoff, medialen);
 		if (ret != NF_ACCEPT)
@@ -950,8 +953,9 @@ static int process_sdp(struct sk_buff *skb,
 
 		/* Update media connection address if present */
 		if (maddr_len && nf_nat_sdp_addr && ct->status & IPS_NAT_MASK) {
-			ret = nf_nat_sdp_addr(skb, dptr, mediaoff, datalen,
-					      c_hdr, SDP_HDR_MEDIA, &rtp_addr);
+			ret = nf_nat_sdp_addr(skb, dataoff, dptr, datalen,
+					      mediaoff, c_hdr, SDP_HDR_MEDIA,
+					      &rtp_addr);
 			if (ret != NF_ACCEPT)
 				return ret;
 		}
@@ -961,14 +965,15 @@ static int process_sdp(struct sk_buff *skb,
 	/* Update session connection and owner addresses */
 	nf_nat_sdp_session = rcu_dereference(nf_nat_sdp_session_hook);
 	if (nf_nat_sdp_session && ct->status & IPS_NAT_MASK)
-		ret = nf_nat_sdp_session(skb, dptr, sdpoff, datalen, &rtp_addr);
+		ret = nf_nat_sdp_session(skb, dataoff, dptr, datalen, sdpoff,
+					 &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,
+static int process_invite_response(struct sk_buff *skb, unsigned int dataoff,
 				   const char **dptr, unsigned int *datalen,
 				   unsigned int cseq, unsigned int code)
 {
@@ -978,13 +983,13 @@ static int process_invite_response(struct sk_buff *skb,
 
 	if ((code >= 100 && code <= 199) ||
 	    (code >= 200 && code <= 299))
-		return process_sdp(skb, dptr, datalen, cseq);
+		return process_sdp(skb, dataoff, dptr, datalen, cseq);
 	else if (help->help.ct_sip_info.invite_cseq == cseq)
 		flush_expectations(ct, true);
 	return NF_ACCEPT;
 }
 
-static int process_update_response(struct sk_buff *skb,
+static int process_update_response(struct sk_buff *skb, unsigned int dataoff,
 				   const char **dptr, unsigned int *datalen,
 				   unsigned int cseq, unsigned int code)
 {
@@ -994,13 +999,13 @@ static int process_update_response(struct sk_buff *skb,
 
 	if ((code >= 100 && code <= 199) ||
 	    (code >= 200 && code <= 299))
-		return process_sdp(skb, dptr, datalen, cseq);
+		return process_sdp(skb, dataoff, dptr, datalen, cseq);
 	else if (help->help.ct_sip_info.invite_cseq == cseq)
 		flush_expectations(ct, true);
 	return NF_ACCEPT;
 }
 
-static int process_prack_response(struct sk_buff *skb,
+static int process_prack_response(struct sk_buff *skb, unsigned int dataoff,
 				  const char **dptr, unsigned int *datalen,
 				  unsigned int cseq, unsigned int code)
 {
@@ -1010,13 +1015,13 @@ static int process_prack_response(struct sk_buff *skb,
 
 	if ((code >= 100 && code <= 199) ||
 	    (code >= 200 && code <= 299))
-		return process_sdp(skb, dptr, datalen, cseq);
+		return process_sdp(skb, dataoff, dptr, datalen, cseq);
 	else if (help->help.ct_sip_info.invite_cseq == cseq)
 		flush_expectations(ct, true);
 	return NF_ACCEPT;
 }
 
-static int process_bye_request(struct sk_buff *skb,
+static int process_bye_request(struct sk_buff *skb, unsigned int dataoff,
 			       const char **dptr, unsigned int *datalen,
 			       unsigned int cseq)
 {
@@ -1031,7 +1036,7 @@ static int process_bye_request(struct sk_buff *skb,
  * signalling connections. The expectation is marked inactive and is activated
  * when receiving a response indicating success from the registrar.
  */
-static int process_register_request(struct sk_buff *skb,
+static int process_register_request(struct sk_buff *skb, unsigned int dataoff,
 				    const char **dptr, unsigned int *datalen,
 				    unsigned int cseq)
 {
@@ -1101,7 +1106,7 @@ static int process_register_request(struct sk_buff *skb,
 
 	nf_nat_sip_expect = rcu_dereference(nf_nat_sip_expect_hook);
 	if (nf_nat_sip_expect && ct->status & IPS_NAT_MASK)
-		ret = nf_nat_sip_expect(skb, dptr, datalen, exp,
+		ret = nf_nat_sip_expect(skb, dataoff, dptr, datalen, exp,
 					matchoff, matchlen);
 	else {
 		if (nf_ct_expect_related(exp) != 0)
@@ -1117,7 +1122,7 @@ store_cseq:
 	return ret;
 }
 
-static int process_register_response(struct sk_buff *skb,
+static int process_register_response(struct sk_buff *skb, unsigned int dataoff,
 				     const char **dptr, unsigned int *datalen,
 				     unsigned int cseq, unsigned int code)
 {
@@ -1127,7 +1132,7 @@ static int process_register_response(struct sk_buff *skb,
 	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 	union nf_inet_addr addr;
 	__be16 port;
-	unsigned int matchoff, matchlen, dataoff = 0;
+	unsigned int matchoff, matchlen, coff = 0;
 	unsigned int expires = 0;
 	int in_contact = 0, ret;
 
@@ -1154,7 +1159,7 @@ static int process_register_response(struct sk_buff *skb,
 	while (1) {
 		unsigned int c_expires = expires;
 
-		ret = ct_sip_parse_header_uri(ct, *dptr, &dataoff, *datalen,
+		ret = ct_sip_parse_header_uri(ct, *dptr, &coff, *datalen,
 					      SIP_HDR_CONTACT, &in_contact,
 					      &matchoff, &matchlen,
 					      &addr, &port);
@@ -1193,13 +1198,13 @@ static const struct sip_handler sip_handlers[] = {
 	SIP_HANDLER("REGISTER", process_register_request, process_register_response),
 };
 
-static int process_sip_response(struct sk_buff *skb,
+static int process_sip_response(struct sk_buff *skb, unsigned int dataoff,
 				const char **dptr, unsigned int *datalen)
 {
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
-	unsigned int matchoff, matchlen;
-	unsigned int code, cseq, dataoff, i;
+	unsigned int matchoff, matchlen, matchend;
+	unsigned int code, cseq, i;
 
 	if (*datalen < strlen("SIP/2.0 200"))
 		return NF_ACCEPT;
@@ -1213,7 +1218,7 @@ static int process_sip_response(struct sk_buff *skb,
 	cseq = simple_strtoul(*dptr + matchoff, NULL, 10);
 	if (!cseq)
 		return NF_DROP;
-	dataoff = matchoff + matchlen + 1;
+	matchend = matchoff + matchlen + 1;
 
 	for (i = 0; i < ARRAY_SIZE(sip_handlers); i++) {
 		const struct sip_handler *handler;
@@ -1221,15 +1226,16 @@ static int process_sip_response(struct sk_buff *skb,
 		handler = &sip_handlers[i];
 		if (handler->response == NULL)
 			continue;
-		if (*datalen < dataoff + handler->len ||
-		    strnicmp(*dptr + dataoff, handler->method, handler->len))
+		if (*datalen < matchend + handler->len ||
+		    strnicmp(*dptr + matchend, handler->method, handler->len))
 			continue;
-		return handler->response(skb, dptr, datalen, cseq, code);
+		return handler->response(skb, dataoff, dptr, datalen,
+					 cseq, code);
 	}
 	return NF_ACCEPT;
 }
 
-static int process_sip_request(struct sk_buff *skb,
+static int process_sip_request(struct sk_buff *skb, unsigned int dataoff,
 			       const char **dptr, unsigned int *datalen)
 {
 	enum ip_conntrack_info ctinfo;
@@ -1254,7 +1260,7 @@ static int process_sip_request(struct sk_buff *skb,
 		if (!cseq)
 			return NF_DROP;
 
-		return handler->request(skb, dptr, datalen, cseq);
+		return handler->request(skb, dataoff, dptr, datalen, cseq);
 	}
 	return NF_ACCEPT;
 }
@@ -1288,13 +1294,13 @@ static int sip_help(struct sk_buff *skb,
 		return NF_ACCEPT;
 
 	if (strnicmp(dptr, "SIP/2.0 ", strlen("SIP/2.0 ")) != 0)
-		ret = process_sip_request(skb, &dptr, &datalen);
+		ret = process_sip_request(skb, dataoff, &dptr, &datalen);
 	else
-		ret = process_sip_response(skb, &dptr, &datalen);
+		ret = process_sip_response(skb, dataoff, &dptr, &datalen);
 
 	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, &dptr, &datalen))
+		if (nf_nat_sip && !nf_nat_sip(skb, dataoff, &dptr, &datalen))
 			ret = NF_DROP;
 	}