X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=secnet.git;a=blobdiff_plain;f=netlink.c;h=76ac91c31679f2d89e39fadd77fbe7764e818a28;hp=b6650eb36f55ccd58910cb6e7203feae5e44fe93;hb=59938e0ed0c8ac267c3715a25a0a3ed27f7a7e47;hpb=d3fe100dfc120244d316e083ce87b1eb130fe4fd diff --git a/netlink.c b/netlink.c index b6650eb..76ac91c 100644 --- a/netlink.c +++ b/netlink.c @@ -1,13 +1,103 @@ /* User-kernel network link */ -/* Each netlink device is actually a router, with its own IP address. - We do things like decreasing the TTL and recalculating the header - checksum, generating ICMP, responding to pings, etc. */ +/* See RFCs 791, 792, 1123 and 1812 */ -/* This is where we have the anti-spoofing paranoia - before sending a - packet to the kernel we check that the tunnel it came over could - reasonably have produced it. */ +/* The netlink device is actually a router. Tunnels are unnumbered + point-to-point lines (RFC1812 section 2.2.7); the router has a + single address (the 'router-id'). */ +/* This is where we currently have the anti-spoofing paranoia - before + sending a packet to the kernel we check that the tunnel it came + over could reasonably have produced it. */ + + +/* Points to note from RFC1812 (which may require changes in this + file): + +3.3.4 Maximum Transmission Unit - MTU + + The MTU of each logical interface MUST be configurable within the + range of legal MTUs for the interface. + + Many Link Layer protocols define a maximum frame size that may be + sent. In such cases, a router MUST NOT allow an MTU to be set which + would allow sending of frames larger than those allowed by the Link + Layer protocol. However, a router SHOULD be willing to receive a + packet as large as the maximum frame size even if that is larger than + the MTU. + +4.2.1 A router SHOULD count datagrams discarded. + +4.2.2.1 Source route options - we probably should implement processing +of source routes, even though mostly the security policy will prevent +their use. + +5.3.13.4 Source Route Options + + A router MUST implement support for source route options in forwarded + packets. A router MAY implement a configuration option that, when + enabled, causes all source-routed packets to be discarded. However, + such an option MUST NOT be enabled by default. + +5.3.13.5 Record Route Option + + Routers MUST support the Record Route option in forwarded packets. + + A router MAY provide a configuration option that, if enabled, will + cause the router to ignore (i.e., pass through unchanged) Record + Route options in forwarded packets. If provided, such an option MUST + default to enabling the record-route. This option should not affect + the processing of Record Route options in datagrams received by the + router itself (in particular, Record Route options in ICMP echo + requests will still be processed according to Section [4.3.3.6]). + +5.3.13.6 Timestamp Option + + Routers MUST support the timestamp option in forwarded packets. A + timestamp value MUST follow the rules given [INTRO:2]. + + If the flags field = 3 (timestamp and prespecified address), the + router MUST add its timestamp if the next prespecified address + matches any of the router's IP addresses. It is not necessary that + the prespecified address be either the address of the interface on + which the packet arrived or the address of the interface over which + it will be sent. + + +4.2.2.7 Fragmentation: RFC 791 Section 3.2 + + Fragmentation, as described in [INTERNET:1], MUST be supported by a + router. + +4.2.2.8 Reassembly: RFC 791 Section 3.2 + + As specified in the corresponding section of [INTRO:2], a router MUST + support reassembly of datagrams that it delivers to itself. + +4.2.2.9 Time to Live: RFC 791 Section 3.2 + + Note in particular that a router MUST NOT check the TTL of a packet + except when forwarding it. + + A router MUST NOT discard a datagram just because it was received + with TTL equal to zero or one; if it is to the router and otherwise + valid, the router MUST attempt to receive it. + + On messages the router originates, the IP layer MUST provide a means + for the transport layer to set the TTL field of every datagram that + is sent. When a fixed TTL value is used, it MUST be configurable. + + +8.1 The Simple Network Management Protocol - SNMP +8.1.1 SNMP Protocol Elements + + Routers MUST be manageable by SNMP [MGT:3]. The SNMP MUST operate + using UDP/IP as its transport and network protocols. + + +*/ + +#include #include "secnet.h" #include "util.h" #include "ipaddr.h" @@ -17,6 +107,19 @@ #define OPT_SOFTROUTE 1 #define OPT_ALLOWROUTE 2 +#define ICMP_TYPE_ECHO_REPLY 0 + +#define ICMP_TYPE_UNREACHABLE 3 +#define ICMP_CODE_NET_UNREACHABLE 0 +#define ICMP_CODE_PROTOCOL_UNREACHABLE 2 +#define ICMP_CODE_FRAGMENTATION_REQUIRED 4 +#define ICMP_CODE_NET_PROHIBITED 13 + +#define ICMP_TYPE_ECHO_REQUEST 8 + +#define ICMP_TYPE_TIME_EXCEEDED 11 +#define ICMP_CODE_TTL_EXCEEDED 0 + /* Generic IP checksum routine */ static inline uint16_t ip_csum(uint8_t *iph,uint32_t count) { @@ -45,30 +148,30 @@ static inline uint16_t ip_csum(uint8_t *iph,uint32_t count) static inline uint16_t ip_fast_csum(uint8_t *iph, uint32_t ihl) { uint32_t sum; - __asm__ __volatile__(" - movl (%1), %0 - subl $4, %2 - jbe 2f - addl 4(%1), %0 - adcl 8(%1), %0 - adcl 12(%1), %0 -1: adcl 16(%1), %0 - lea 4(%1), %1 - decl %2 - jne 1b - adcl $0, %0 - movl %0, %2 - shrl $16, %0 - addw %w2, %w0 - adcl $0, %0 - notl %0 -2: - " + __asm__ __volatile__( + "movl (%1), %0 ;\n" + "subl $4, %2 ;\n" + "jbe 2f ;\n" + "addl 4(%1), %0 ;\n" + "adcl 8(%1), %0 ;\n" + "adcl 12(%1), %0 ;\n" +"1: adcl 16(%1), %0 ;\n" + "lea 4(%1), %1 ;\n" + "decl %2 ;\n" + "jne 1b ;\n" + "adcl $0, %0 ;\n" + "movl %0, %2 ;\n" + "shrl $16, %0 ;\n" + "addw %w2, %w0 ;\n" + "adcl $0, %0 ;\n" + "notl %0 ;\n" +"2: ;\n" /* Since the input registers which are loaded with iph and ipl are modified, we must also specify them as outputs, or gcc will assume they contain their original values. */ : "=r" (sum), "=r" (iph), "=r" (ihl) - : "1" (iph), "2" (ihl)); + : "1" (iph), "2" (ihl) + : "memory"); return sum; } #else @@ -122,6 +225,13 @@ static void netlink_packet_deliver(struct netlink *st, struct netlink_client *client, struct buffer_if *buf); +/* XXX RFC1812 4.3.2.5: + All other ICMP error messages (Destination Unreachable, + Redirect, Time Exceeded, and Parameter Problem) SHOULD have their + precedence value set to 6 (INTERNETWORK CONTROL) or 7 (NETWORK + CONTROL). The IP Precedence value for these error messages MAY be + settable. + */ static struct icmphdr *netlink_icmp_tmpl(struct netlink *st, uint32_t dest,uint16_t len) { @@ -137,7 +247,7 @@ static struct icmphdr *netlink_icmp_tmpl(struct netlink *st, h->iph.tot_len=htons(len+(h->iph.ihl*4)+8); h->iph.id=0; h->iph.frag_off=0; - h->iph.ttl=255; + h->iph.ttl=255; /* XXX should be configurable */ h->iph.protocol=1; h->iph.saddr=htonl(st->secnet_address); h->iph.daddr=htonl(dest); @@ -206,6 +316,26 @@ static bool_t netlink_icmp_may_reply(struct buffer_if *buf) /* How much of the original IP packet do we include in its ICMP response? The header plus up to 64 bits. */ + +/* XXX TODO RFC1812: +4.3.2.3 Original Message Header + + Historically, every ICMP error message has included the Internet + header and at least the first 8 data bytes of the datagram that + triggered the error. This is no longer adequate, due to the use of + IP-in-IP tunneling and other technologies. Therefore, the ICMP + datagram SHOULD contain as much of the original datagram as possible + without the length of the ICMP datagram exceeding 576 bytes. The + returned IP header (and user data) MUST be identical to that which + was received, except that the router is not required to undo any + modifications to the IP header that are normally performed in + forwarding that were performed before the error was detected (e.g., + decrementing the TTL, or updating options). Note that the + requirements of Section [4.3.3.5] supersede this requirement in some + cases (i.e., for a Parameter Problem message, if the problem is in a + modified field, the router must undo the modification). See Section + [4.3.3.5]). + */ static uint16_t netlink_icmp_reply_len(struct buffer_if *buf) { struct iphdr *iph=(struct iphdr *)buf->start; @@ -242,6 +372,7 @@ static void netlink_icmp_simple(struct netlink *st, struct buffer_if *buf, /* * RFC1122: 3.1.2.2 MUST silently discard any IP frame that fails the * checksum. + * RFC1812: 4.2.2.5 MUST discard messages containing invalid checksums. * * Is the datagram acceptable? * @@ -284,7 +415,7 @@ static void netlink_packet_deliver(struct netlink *st, BUF_ASSERT_USED(buf); if (dest==st->secnet_address) { - Message(M_ERR,"%s: trying to deliver a packet to myself!\n"); + Message(M_ERR,"%s: trying to deliver a packet to myself!\n",st->name); BUF_FREE(buf); return; } @@ -344,10 +475,11 @@ static void netlink_packet_deliver(struct netlink *st, string_t s,d; s=ipaddr_to_string(source); d=ipaddr_to_string(dest); - Message(M_ERR,"%s: don't know where to deliver packet " + Message(M_DEBUG,"%s: don't know where to deliver packet " "(s=%s, d=%s)\n", st->name, s, d); free(s); free(d); - netlink_icmp_simple(st,buf,client,3,0); + netlink_icmp_simple(st,buf,client,ICMP_TYPE_UNREACHABLE, + ICMP_CODE_NET_UNREACHABLE); BUF_FREE(buf); } } else { @@ -363,19 +495,22 @@ static void netlink_packet_deliver(struct netlink *st, st->name,s,d); free(s); free(d); - netlink_icmp_simple(st,buf,client,3,9); + netlink_icmp_simple(st,buf,client,ICMP_TYPE_UNREACHABLE, + ICMP_CODE_NET_PROHIBITED); BUF_FREE(buf); - } - if (best_quality>0) { - /* XXX Fragment if required */ - st->routes[best_match]->deliver( - st->routes[best_match]->dst, buf); - st->routes[best_match]->outcount++; - BUF_ASSERT_FREE(buf); } else { - /* Generate ICMP destination unreachable */ - netlink_icmp_simple(st,buf,client,3,0); /* client==NULL */ - BUF_FREE(buf); + if (best_quality>0) { + /* XXX Fragment if required */ + st->routes[best_match]->deliver( + st->routes[best_match]->dst, buf); + st->routes[best_match]->outcount++; + BUF_ASSERT_FREE(buf); + } else { + /* Generate ICMP destination unreachable */ + netlink_icmp_simple(st,buf,client,ICMP_TYPE_UNREACHABLE, + ICMP_CODE_NET_UNREACHABLE); /* client==NULL */ + BUF_FREE(buf); + } } } BUF_ASSERT_FREE(buf); @@ -392,7 +527,8 @@ static void netlink_packet_forward(struct netlink *st, /* Packet has already been checked */ if (iph->ttl<=1) { /* Generate ICMP time exceeded */ - netlink_icmp_simple(st,buf,client,11,0); + netlink_icmp_simple(st,buf,client,ICMP_TYPE_TIME_EXCEEDED, + ICMP_CODE_TTL_EXCEEDED); BUF_FREE(buf); return; } @@ -424,13 +560,13 @@ static void netlink_packet_local(struct netlink *st, if (h->iph.protocol==1) { /* It's ICMP */ - if (h->type==8 && h->code==0) { + if (h->type==ICMP_TYPE_ECHO_REQUEST && h->code==0) { /* ICMP echo-request. Special case: we re-use the buffer to construct the reply. */ - h->type=0; + h->type=ICMP_TYPE_ECHO_REPLY; h->iph.daddr=h->iph.saddr; h->iph.saddr=htonl(st->secnet_address); - h->iph.ttl=255; /* Be nice and bump it up again... */ + h->iph.ttl=255; h->iph.check=0; h->iph.check=ip_fast_csum((uint8_t *)h,h->iph.ihl); netlink_icmp_csum(h); @@ -440,7 +576,8 @@ static void netlink_packet_local(struct netlink *st, Message(M_WARNING,"%s: unknown incoming ICMP\n",st->name); } else { /* Send ICMP protocol unreachable */ - netlink_icmp_simple(st,buf,client,3,2); + netlink_icmp_simple(st,buf,client,ICMP_TYPE_UNREACHABLE, + ICMP_CODE_PROTOCOL_UNREACHABLE); BUF_FREE(buf); return; } @@ -584,13 +721,16 @@ static void netlink_dump_routes(struct netlink *st, bool_t requested) Message(c,"%s: routing table:\n",st->name); for (i=0; in_clients; i++) { netlink_output_subnets(st,c,st->routes[i]->subnets); - Message(c,"-> tunnel %s (%s,%s routes,%s,quality %d,use %d)\n", + Message(c,"-> tunnel %s (%s,mtu %d,%s routes,%s," + "quality %d,use %d,pri %lu)\n", st->routes[i]->name, + st->routes[i]->up?"up":"down", + st->routes[i]->mtu, st->routes[i]->options&OPT_SOFTROUTE?"soft":"hard", st->routes[i]->options&OPT_ALLOWROUTE?"free":"restricted", - st->routes[i]->up?"up":"down", st->routes[i]->link_quality, - st->routes[i]->outcount); + st->routes[i]->outcount, + (unsigned long)st->routes[i]->priority); } net=ipaddr_to_string(st->secnet_address); Message(c,"%s/32 -> netlink \"%s\" (use %d)\n", @@ -798,7 +938,7 @@ static list_t *netlink_inst_apply(closure_t *self, struct cloc loc, netlink_deliver_fn *netlink_init(struct netlink *st, void *dst, struct cloc loc, - dict_t *dict, string_t description, + dict_t *dict, cstring_t description, netlink_route_fn *set_routes, netlink_deliver_fn *to_host) { @@ -824,9 +964,10 @@ netlink_deliver_fn *netlink_init(struct netlink *st, if (l) st->networks=string_list_to_ipset(l,loc,st->name,"networks"); else { - Message(M_WARNING,"%s: no local networks (parameter \"networks\") " - "defined\n",st->name); - st->networks=ipset_new(); + struct ipset *empty; + empty=ipset_new(); + st->networks=ipset_complement(empty); + ipset_free(empty); } l=dict_lookup(dict,"remote-networks"); if (l) { @@ -926,7 +1067,6 @@ static list_t *null_apply(closure_t *self, struct cloc loc, dict_t *context, return new_closure(&st->nl.cl); } -init_module netlink_module; void netlink_module(dict_t *dict) { add_closure(dict,"null-netlink",null_apply);