diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index 182cfb119448..1eb55907d470 100644
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -181,6 +181,57 @@ static int sip_parse_addr(const struct nf_conn *ct, const char *cp,
 	return 1;
 }
 
+/* Parse optional port number after IP address.
+ * Returns false on malformed input, true otherwise.
+ * If port is non-NULL, stores parsed port in network byte order.
+ * If no port is present, sets *port to default SIP port.
+ */
+static bool sip_parse_port(const char *dptr, const char **endp,
+			   const char *limit, __be16 *port)
+{
+	unsigned int p = 0;
+	int len = 0;
+
+	if (dptr >= limit)
+		return false;
+
+	if (*dptr != ':') {
+		if (port)
+			*port = htons(SIP_PORT);
+		if (endp)
+			*endp = dptr;
+		return true;
+	}
+
+	dptr++; /* skip ':' */
+
+	while (dptr < limit && isdigit(*dptr)) {
+		p = p * 10 + (*dptr - '0');
+		dptr++;
+		len++;
+		if (len > 5) /* max "65535" */
+			return false;
+	}
+
+	if (len == 0)
+		return false;
+
+	/* reached limit while parsing port */
+	if (dptr >= limit)
+		return false;
+
+	if (p < 1024 || p > 65535)
+		return false;
+
+	if (port)
+		*port = htons(p);
+
+	if (endp)
+		*endp = dptr;
+
+	return true;
+}
+
 /* skip ip address. returns its length. */
 static int epaddr_len(const struct nf_conn *ct, const char *dptr,
 		      const char *limit, int *shift)
@@ -193,11 +244,8 @@ static int epaddr_len(const struct nf_conn *ct, const char *dptr,
 		return 0;
 	}
 
-	/* Port number */
-	if (*dptr == ':') {
-		dptr++;
-		dptr += digits_len(ct, dptr, limit, shift);
-	}
+	if (!sip_parse_port(dptr, &dptr, limit, NULL))
+		return 0;
 	return dptr - aux;
 }
 
@@ -228,6 +276,51 @@ static int skp_epaddr_len(const struct nf_conn *ct, const char *dptr,
 	return epaddr_len(ct, dptr, limit, shift);
 }
 
+/* simple_strtoul stops after first non-number character.
+ * But as we're not dealing with c-strings, we can't rely on
+ * hitting \r,\n,\0 etc. before moving past end of buffer.
+ *
+ * This is a variant of simple_strtoul, but doesn't require
+ * a c-string.
+ *
+ * If value exceeds UINT_MAX, 0 is returned.
+ */
+static unsigned int sip_strtouint(const char *cp, unsigned int len, char **endp)
+{
+	const unsigned int max = sizeof("4294967295");
+	unsigned int olen = len;
+	const char *s = cp;
+	u64 result = 0;
+
+	if (len > max)
+		len = max;
+
+	while (olen > 0 && isdigit(*s)) {
+		unsigned int value;
+
+		if (len == 0)
+			goto err;
+
+		value = *s - '0';
+		result = result * 10 + value;
+
+		if (result > UINT_MAX)
+			goto err;
+		s++;
+		len--;
+		olen--;
+	}
+
+	if (endp)
+		*endp = (char *)s;
+
+	return result;
+err:
+	if (endp)
+		*endp = (char *)cp;
+	return 0;
+}
+
 /* Parse a SIP request line of the form:
  *
  * Request-Line = Method SP Request-URI SP SIP-Version CRLF
@@ -241,7 +334,6 @@ int ct_sip_parse_request(const struct nf_conn *ct,
 {
 	const char *start = dptr, *limit = dptr + datalen, *end;
 	unsigned int mlen;
-	unsigned int p;
 	int shift = 0;
 
 	/* Skip method and following whitespace */
@@ -267,14 +359,8 @@ int ct_sip_parse_request(const struct nf_conn *ct,
 
 	if (!sip_parse_addr(ct, dptr, &end, addr, limit, true))
 		return -1;
-	if (end < limit && *end == ':') {
-		end++;
-		p = simple_strtoul(end, (char **)&end, 10);
-		if (p < 1024 || p > 65535)
-			return -1;
-		*port = htons(p);
-	} else
-		*port = htons(SIP_PORT);
+	if (!sip_parse_port(end, &end, limit, port))
+		return -1;
 
 	if (end == dptr)
 		return 0;
@@ -509,7 +595,6 @@ int ct_sip_parse_header_uri(const struct nf_conn *ct, const char *dptr,
 			    union nf_inet_addr *addr, __be16 *port)
 {
 	const char *c, *limit = dptr + datalen;
-	unsigned int p;
 	int ret;
 
 	ret = ct_sip_walk_headers(ct, dptr, dataoff ? *dataoff : 0, datalen,
@@ -520,14 +605,8 @@ int ct_sip_parse_header_uri(const struct nf_conn *ct, const char *dptr,
 
 	if (!sip_parse_addr(ct, dptr + *matchoff, &c, addr, limit, true))
 		return -1;
-	if (*c == ':') {
-		c++;
-		p = simple_strtoul(c, (char **)&c, 10);
-		if (p < 1024 || p > 65535)
-			return -1;
-		*port = htons(p);
-	} else
-		*port = htons(SIP_PORT);
+	if (!sip_parse_port(c, &c, limit, port))
+		return -1;
 
 	if (dataoff)
 		*dataoff = c - dptr;
@@ -609,7 +688,7 @@ int ct_sip_parse_numerical_param(const struct nf_conn *ct, const char *dptr,
 		return 0;
 
 	start += strlen(name);
-	*val = simple_strtoul(start, &end, 0);
+	*val = sip_strtouint(start, limit - start, (char **)&end);
 	if (start == end)
 		return -1;
 	if (matchoff && matchlen) {
@@ -1064,6 +1143,8 @@ static int process_sdp(struct sk_buff *skb, unsigned int protoff,
 
 	mediaoff = sdpoff;
 	for (i = 0; i < ARRAY_SIZE(sdp_media_types); ) {
+		char *end;
+
 		if (ct_sip_get_sdp_header(ct, *dptr, mediaoff, *datalen,
 					  SDP_HDR_MEDIA, SDP_HDR_UNSPEC,
 					  &mediaoff, &medialen) <= 0)
@@ -1079,8 +1160,8 @@ static int process_sdp(struct sk_buff *skb, unsigned int protoff,
 		mediaoff += t->len;
 		medialen -= t->len;
 
-		port = simple_strtoul(*dptr + mediaoff, NULL, 10);
-		if (port == 0)
+		port = sip_strtouint(*dptr + mediaoff, *datalen - mediaoff, (char **)&end);
+		if (port == 0 || *dptr + mediaoff == end)
 			continue;
 		if (port < 1024 || port > 65535) {
 			nf_ct_helper_log(skb, ct, "wrong port %u", port);
@@ -1254,7 +1335,7 @@ static int process_register_request(struct sk_buff *skb, unsigned int protoff,
 	 */
 	if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_EXPIRES,
 			      &matchoff, &matchlen) > 0)
-		expires = simple_strtoul(*dptr + matchoff, NULL, 10);
+		expires = sip_strtouint(*dptr + matchoff, *datalen - matchoff, NULL);
 
 	ret = ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen,
 				      SIP_HDR_CONTACT, NULL,
@@ -1358,7 +1439,7 @@ static int process_register_response(struct sk_buff *skb, unsigned int protoff,
 
 	if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_EXPIRES,
 			      &matchoff, &matchlen) > 0)
-		expires = simple_strtoul(*dptr + matchoff, NULL, 10);
+		expires = sip_strtouint(*dptr + matchoff, *datalen - matchoff, NULL);
 
 	while (1) {
 		unsigned int c_expires = expires;
@@ -1418,10 +1499,12 @@ static int process_sip_response(struct sk_buff *skb, unsigned int protoff,
 	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 	unsigned int matchoff, matchlen, matchend;
 	unsigned int code, cseq, i;
+	char *end;
 
 	if (*datalen < strlen("SIP/2.0 200"))
 		return NF_ACCEPT;
-	code = simple_strtoul(*dptr + strlen("SIP/2.0 "), NULL, 10);
+	code = sip_strtouint(*dptr + strlen("SIP/2.0 "),
+			     *datalen - strlen("SIP/2.0 "), NULL);
 	if (!code) {
 		nf_ct_helper_log(skb, ct, "cannot get code");
 		return NF_DROP;
@@ -1432,8 +1515,8 @@ static int process_sip_response(struct sk_buff *skb, unsigned int protoff,
 		nf_ct_helper_log(skb, ct, "cannot parse cseq");
 		return NF_DROP;
 	}
-	cseq = simple_strtoul(*dptr + matchoff, NULL, 10);
-	if (!cseq && *(*dptr + matchoff) != '0') {
+	cseq = sip_strtouint(*dptr + matchoff, *datalen - matchoff, (char **)&end);
+	if (*dptr + matchoff == end) {
 		nf_ct_helper_log(skb, ct, "cannot get cseq");
 		return NF_DROP;
 	}
@@ -1482,6 +1565,7 @@ static int process_sip_request(struct sk_buff *skb, unsigned int protoff,
 
 	for (i = 0; i < ARRAY_SIZE(sip_handlers); i++) {
 		const struct sip_handler *handler;
+		char *end;
 
 		handler = &sip_handlers[i];
 		if (handler->request == NULL)
@@ -1498,8 +1582,8 @@ static int process_sip_request(struct sk_buff *skb, unsigned int protoff,
 			nf_ct_helper_log(skb, ct, "cannot parse cseq");
 			return NF_DROP;
 		}
-		cseq = simple_strtoul(*dptr + matchoff, NULL, 10);
-		if (!cseq && *(*dptr + matchoff) != '0') {
+		cseq = sip_strtouint(*dptr + matchoff, *datalen - matchoff, (char **)&end);
+		if (*dptr + matchoff == end) {
 			nf_ct_helper_log(skb, ct, "cannot get cseq");
 			return NF_DROP;
 		}
@@ -1575,7 +1659,7 @@ static int sip_help_tcp(struct sk_buff *skb, unsigned int protoff,
 				      &matchoff, &matchlen) <= 0)
 			break;
 
-		clen = simple_strtoul(dptr + matchoff, (char **)&end, 10);
+		clen = sip_strtouint(dptr + matchoff, datalen - matchoff, (char **)&end);
 		if (dptr + matchoff == end)
 			break;
 
diff --git a/net/netfilter/nf_nat_sip.c b/net/netfilter/nf_nat_sip.c
index c845b6d1a2bd..9fbfc6bff0c2 100644
--- a/net/netfilter/nf_nat_sip.c
+++ b/net/netfilter/nf_nat_sip.c
@@ -246,6 +246,7 @@ static unsigned int nf_nat_sip(struct sk_buff *skb, unsigned int protoff,
 		if (ct_sip_parse_numerical_param(ct, *dptr, matchend, *datalen,
 						 "rport=", &poff, &plen,
 						 &n) > 0 &&
+		    n >= 1024 && n <= 65535 &&
 		    htons(n) == ct->tuplehash[dir].tuple.dst.u.udp.port &&
 		    htons(n) != ct->tuplehash[!dir].tuple.src.u.udp.port) {
 			__be16 p = ct->tuplehash[!dir].tuple.src.u.udp.port;