[NETFILTER]: sip conntrack: better NAT handling

The NAT handling of the SIP helper has a few problems:

- Request headers are only mangled in the reply direction, From/To headers
  not at all, which can lead to authentication failures with DNAT in case
  the authentication domain is the IP address

- Contact headers in responses are only mangled for REGISTER responses

- Headers may be mangled even though they contain addresses not
  participating in the connection, like alternative addresses

- Packets are droppen when domain names are used where the helper expects
  IP addresses

This patch takes a different approach, instead of fixed rules what field
to mangle to what content, it adds symetric mapping of From/To/Via/Contact
headers, which allows to deal properly with echoed addresses in responses
and foreign addresses not belonging to the connection.

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

2 files changed, 131 insertions, 69 deletions

diff --git a/net/ipv4/netfilter/ip_conntrack_sip.c b/net/ipv4/netfilter/ip_conntrack_sip.c
index 0a6a13c45b07..3a26d63eed88 100644
--- a/net/ipv4/netfilter/ip_conntrack_sip.c
+++ b/net/ipv4/netfilter/ip_conntrack_sip.c
@@ -69,13 +69,38 @@ struct sip_header_nfo {
 };
 
 static struct sip_header_nfo ct_sip_hdrs[] = {
-        [POS_REQ_HEADER] = {    /* SIP Requests headers */
+        [POS_REG_REQ_URI] = {   /* SIP REGISTER request URI */
+                .lname          = "sip:",
+                .lnlen          = sizeof("sip:") - 1,
+                .ln_str         = ":",
+                .ln_strlen      = sizeof(":") - 1,
+                .match_len      = epaddr_len
+        },
+        [POS_REQ_URI] = {       /* SIP request URI */
                 .lname          = "sip:",
                 .lnlen          = sizeof("sip:") - 1,
                 .ln_str         = "@",
                 .ln_strlen      = sizeof("@") - 1,
                 .match_len      = epaddr_len
         },
+        [POS_FROM] = {          /* SIP From header */
+                .lname          = "From:",
+                .lnlen          = sizeof("From:") - 1,
+                .sname          = "\r\nf:",
+                .snlen          = sizeof("\r\nf:") - 1,
+                .ln_str         = "sip:",
+                .ln_strlen      = sizeof("sip:") - 1,
+                .match_len      = skp_epaddr_len,
+        },
+        [POS_TO] = {            /* SIP To header */
+                .lname          = "To:",
+                .lnlen          = sizeof("To:") - 1,
+                .sname          = "\r\nt:",
+                .snlen          = sizeof("\r\nt:") - 1,
+                .ln_str         = "sip:",
+                .ln_strlen      = sizeof("sip:") - 1,
+                .match_len      = skp_epaddr_len,
+        },
         [POS_VIA] = {           /* SIP Via header */
                 .lname          = "Via:",
                 .lnlen          = sizeof("Via:") - 1,
@@ -284,7 +309,7 @@ int ct_sip_get_info(const char *dptr, size_t dlen,
 
         while (dptr <= limit) {
                 if ((strncmp(dptr, hnfo->lname, hnfo->lnlen) != 0) &&
-                    (hinfo->sname == NULL ||
+                    (hnfo->sname == NULL ||
                      strncmp(dptr, hnfo->sname, hnfo->snlen) != 0)) {
                         dptr++;
                         continue;
diff --git a/net/ipv4/netfilter/ip_nat_sip.c b/net/ipv4/netfilter/ip_nat_sip.c
index e16604c4339d..6223abc924ff 100644
--- a/net/ipv4/netfilter/ip_nat_sip.c
+++ b/net/ipv4/netfilter/ip_nat_sip.c
@@ -29,25 +29,70 @@ MODULE_DESCRIPTION("SIP NAT helper");
 #define DEBUGP(format, args...)
 #endif
 
-static unsigned int mangle_sip_packet(struct sk_buff **pskb,
-                                      enum ip_conntrack_info ctinfo,
-                                      struct ip_conntrack *ct,
-                                      const char **dptr, size_t dlen,
-                                      char *buffer, int bufflen,
-                                      enum sip_header_pos pos)
+struct addr_map {
+        struct {
+                char            src[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
+                char            dst[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
+                unsigned int    srclen, srciplen;
+                unsigned int    dstlen, dstiplen;
+        } addr[IP_CT_DIR_MAX];
+};
+
+static void addr_map_init(struct ip_conntrack *ct, struct addr_map *map)
 {
-        unsigned int matchlen, matchoff;
+        struct ip_conntrack_tuple *t;
+        enum ip_conntrack_dir dir;
+        unsigned int n;
+
+        for (dir = 0; dir < IP_CT_DIR_MAX; dir++) {
+                t = &ct->tuplehash[dir].tuple;
+
+                n = sprintf(map->addr[dir].src, "%u.%u.%u.%u",
+                            NIPQUAD(t->src.ip));
+                map->addr[dir].srciplen = n;
+                n += sprintf(map->addr[dir].src + n, ":%u",
+                             ntohs(t->src.u.udp.port));
+                map->addr[dir].srclen = n;
+
+                n = sprintf(map->addr[dir].dst, "%u.%u.%u.%u",
+                            NIPQUAD(t->dst.ip));
+                map->addr[dir].dstiplen = n;
+                n += sprintf(map->addr[dir].dst + n, ":%u",
+                             ntohs(t->dst.u.udp.port));
+                map->addr[dir].dstlen = n;
+        }
+}
+
+static int map_sip_addr(struct sk_buff **pskb, enum ip_conntrack_info ctinfo,
+                        struct ip_conntrack *ct, const char **dptr, size_t dlen,
+                        enum sip_header_pos pos, struct addr_map *map)
+{
+        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+        unsigned int matchlen, matchoff, addrlen;
+        char *addr;
 
         if (ct_sip_get_info(*dptr, dlen, &matchoff, &matchlen, pos) <= 0)
-                return 0;
+                return 1;
+
+        if ((matchlen == map->addr[dir].srciplen ||
+             matchlen == map->addr[dir].srclen) &&
+            memcmp(*dptr + matchoff, map->addr[dir].src, matchlen) == 0) {
+                addr    = map->addr[!dir].dst;
+                addrlen = map->addr[!dir].dstlen;
+        } else if ((matchlen == map->addr[dir].dstiplen ||
+                    matchlen == map->addr[dir].dstlen) &&
+                   memcmp(*dptr + matchoff, map->addr[dir].dst, matchlen) == 0) {
+                addr    = map->addr[!dir].src;
+                addrlen = map->addr[!dir].srclen;
+        } else
+                return 1;
 
         if (!ip_nat_mangle_udp_packet(pskb, ct, ctinfo,
-                                      matchoff, matchlen, buffer, bufflen))
+                                      matchoff, matchlen, addr, addrlen))
                 return 0;
-
-        /* We need to reload this. Thanks Patrick. */
         *dptr = (*pskb)->data + (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
         return 1;
+
 }
 
 static unsigned int ip_nat_sip(struct sk_buff **pskb,
@@ -55,69 +100,61 @@ static unsigned int ip_nat_sip(struct sk_buff **pskb,
                                struct ip_conntrack *ct,
                                const char **dptr)
 {
-        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
-        char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
-        unsigned int bufflen, dataoff;
-        __be32 ip;
-        __be16 port;
+        enum sip_header_pos pos;
+        struct addr_map map;
+        int dataoff, datalen;
 
         dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
+        datalen = (*pskb)->len - dataoff;
+        if (datalen < sizeof("SIP/2.0") - 1)
+                return NF_DROP;
+
+        addr_map_init(ct, &map);
+
+        /* Basic rules: requests and responses. */
+        if (strncmp(*dptr, "SIP/2.0", sizeof("SIP/2.0") - 1) != 0) {
+                /* 10.2: Constructing the REGISTER Request:
+                 *
+                 * The "userinfo" and "@" components of the SIP URI MUST NOT
+                 * be present.
+                 */
+                if (datalen >= sizeof("REGISTER") - 1 &&
+                    strncmp(*dptr, "REGISTER", sizeof("REGISTER") - 1) == 0)
+                        pos = POS_REG_REQ_URI;
+                else
+                        pos = POS_REQ_URI;
+
+                if (!map_sip_addr(pskb, ctinfo, ct, dptr, datalen, pos, &map))
+                        return NF_DROP;
+        }
 
-        ip   = ct->tuplehash[!dir].tuple.dst.ip;
-        port = ct->tuplehash[!dir].tuple.dst.u.udp.port;
-        bufflen = sprintf(buffer, "%u.%u.%u.%u:%u", NIPQUAD(ip), ntohs(port));
+        if (!map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_FROM, &map) ||
+            !map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_TO, &map) ||
+            !map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_VIA, &map) ||
+            !map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_CONTACT, &map))
+                return NF_DROP;
+        return NF_ACCEPT;
+}
+
+static unsigned int mangle_sip_packet(struct sk_buff **pskb,
+                                      enum ip_conntrack_info ctinfo,
+                                      struct ip_conntrack *ct,
+                                      const char **dptr, size_t dlen,
+                                      char *buffer, int bufflen,
+                                      enum sip_header_pos pos)
+{
+        unsigned int matchlen, matchoff;
 
-        /* short packet ? */
-        if (((*pskb)->len - dataoff) < (sizeof("SIP/2.0") - 1))
+        if (ct_sip_get_info(*dptr, dlen, &matchoff, &matchlen, pos) <= 0)
                 return 0;
 
-        /* Basic rules: requests and responses. */
-        if (memcmp(*dptr, "SIP/2.0", sizeof("SIP/2.0") - 1) == 0) {
-                const char *aux;
-
-                if ((ctinfo) < IP_CT_IS_REPLY) {
-                        mangle_sip_packet(pskb, ctinfo, ct, dptr,
-                                          (*pskb)->len - dataoff,
-                                          buffer, bufflen, POS_CONTACT);
-                        return 1;
-                }
+        if (!ip_nat_mangle_udp_packet(pskb, ct, ctinfo,
+                                      matchoff, matchlen, buffer, bufflen))
+                return 0;
 
-                if (!mangle_sip_packet(pskb, ctinfo, ct, dptr,
-                                       (*pskb)->len - dataoff,
-                                       buffer, bufflen, POS_VIA))
-                        return 0;
-
-                aux = ct_sip_search("CSeq:", *dptr, sizeof("CSeq:") - 1,
-                                    (*pskb)->len - dataoff, 0);
-                if (!aux)
-                        return 0;
-
-                if (!ct_sip_search("REGISTER", aux, sizeof("REGISTER"),
-                                   ct_sip_lnlen(aux,
-                                                *dptr + (*pskb)->len - dataoff),
-                                   1))
-                        return 1;
-
-                return mangle_sip_packet(pskb, ctinfo, ct, dptr,
-                                         (*pskb)->len - dataoff,
-                                         buffer, bufflen, POS_CONTACT);
-        }
-        if ((ctinfo) < IP_CT_IS_REPLY) {
-                if (!mangle_sip_packet(pskb, ctinfo, ct, dptr,
-                                       (*pskb)->len - dataoff,
-                                       buffer, bufflen, POS_VIA))
-                        return 0;
-
-                /* Mangle Contact if exists only. - watch udp_nat_mangle()! */
-                mangle_sip_packet(pskb, ctinfo, ct, dptr, (*pskb)->len - dataoff,
-                                  buffer, bufflen, POS_CONTACT);
-                return 1;
-        }
-        /* This mangle requests headers. */
-        return mangle_sip_packet(pskb, ctinfo, ct, dptr,
-                                 ct_sip_lnlen(*dptr,
-                                              *dptr + (*pskb)->len - dataoff),
-                                 buffer, bufflen, POS_REQ_HEADER);
+        /* We need to reload this. Thanks Patrick. */
+        *dptr = (*pskb)->data + (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
+        return 1;
 }
 
 static int mangle_content_len(struct sk_buff **pskb,