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Diffstat (limited to 'src/smtp/smtp_addr.c')
| -rw-r--r-- | src/smtp/smtp_addr.c | 693 |
1 files changed, 693 insertions, 0 deletions
diff --git a/src/smtp/smtp_addr.c b/src/smtp/smtp_addr.c new file mode 100644 index 0000000..2210ff7 --- /dev/null +++ b/src/smtp/smtp_addr.c @@ -0,0 +1,693 @@ +/*++ +/* NAME +/* smtp_addr 3 +/* SUMMARY +/* SMTP server address lookup +/* SYNOPSIS +/* #include "smtp_addr.h" +/* +/* DNS_RR *smtp_domain_addr(name, mxrr, misc_flags, why, found_myself) +/* char *name; +/* DNS_RR **mxrr; +/* int misc_flags; +/* DSN_BUF *why; +/* int *found_myself; +/* +/* DNS_RR *smtp_host_addr(name, misc_flags, why) +/* char *name; +/* int misc_flags; +/* DSN_BUF *why; +/* DESCRIPTION +/* This module implements Internet address lookups. By default, +/* lookups are done via the Internet domain name service (DNS). +/* A reasonable number of CNAME indirections is permitted. When +/* DNS lookups are disabled, host address lookup is done with +/* getnameinfo() or gethostbyname(). +/* +/* smtp_domain_addr() looks up the network addresses for mail +/* exchanger hosts listed for the named domain. Addresses are +/* returned in most-preferred first order. The result is truncated +/* so that it contains only hosts that are more preferred than the +/* local mail server itself. The found_myself result parameter +/* is updated when the local MTA is MX host for the specified +/* destination. If MX records were found, the rname, qname, +/* and dnssec validation status of the MX RRset are returned +/* via mxrr, which the caller must free with dns_rr_free(). +/* +/* When no mail exchanger is listed in the DNS for \fIname\fR, the +/* request is passed to smtp_host_addr(). +/* +/* It is an error to call smtp_domain_addr() when DNS lookups are +/* disabled. +/* +/* smtp_host_addr() looks up all addresses listed for the named +/* host. The host can be specified as a numerical Internet network +/* address, or as a symbolic host name. +/* +/* Results from smtp_domain_addr() or smtp_host_addr() are +/* destroyed by dns_rr_free(), including null lists. +/* DIAGNOSTICS +/* Panics: interface violations. For example, calling smtp_domain_addr() +/* when DNS lookups are explicitly disabled. +/* +/* All routines either return a DNS_RR pointer, or return a null +/* pointer and update the \fIwhy\fR argument accordingly. +/* LICENSE +/* .ad +/* .fi +/* The Secure Mailer license must be distributed with this software. +/* AUTHOR(S) +/* Wietse Venema +/* IBM T.J. Watson Research +/* P.O. Box 704 +/* Yorktown Heights, NY 10598, USA +/* +/* Wietse Venema +/* Google, Inc. +/* 111 8th Avenue +/* New York, NY 10011, USA +/*--*/ + +/* System library. */ + +#include <sys_defs.h> +#include <sys/socket.h> +#include <netinet/in.h> +#include <arpa/inet.h> +#include <stdlib.h> +#include <netdb.h> +#include <ctype.h> +#include <string.h> +#include <unistd.h> +#include <errno.h> + +/* Utility library. */ + +#include <msg.h> +#include <vstring.h> +#include <mymalloc.h> +#include <inet_addr_list.h> +#include <stringops.h> +#include <myaddrinfo.h> +#include <inet_proto.h> +#include <midna_domain.h> + +/* Global library. */ + +#include <mail_params.h> +#include <own_inet_addr.h> +#include <dsn_buf.h> + +/* DNS library. */ + +#include <dns.h> + +/* Application-specific. */ + +#include "smtp.h" +#include "smtp_addr.h" + +/* smtp_print_addr - print address list */ + +static void smtp_print_addr(const char *what, DNS_RR *addr_list) +{ + DNS_RR *addr; + MAI_HOSTADDR_STR hostaddr; + + msg_info("begin %s address list", what); + for (addr = addr_list; addr; addr = addr->next) { + if (dns_rr_to_pa(addr, &hostaddr) == 0) { + msg_warn("skipping record type %s: %m", dns_strtype(addr->type)); + } else { + msg_info("pref %4d host %s/%s", + addr->pref, SMTP_HNAME(addr), + hostaddr.buf); + } + } + msg_info("end %s address list", what); +} + +/* smtp_addr_one - address lookup for one host name */ + +static DNS_RR *smtp_addr_one(DNS_RR *addr_list, const char *host, int res_opt, + unsigned pref, DSN_BUF *why) +{ + const char *myname = "smtp_addr_one"; + DNS_RR *addr = 0; + DNS_RR *rr; + int aierr; + struct addrinfo *res0; + struct addrinfo *res; + INET_PROTO_INFO *proto_info = inet_proto_info(); + unsigned char *proto_family_list = proto_info->sa_family_list; + int found; + + if (msg_verbose) + msg_info("%s: host %s", myname, host); + + /* + * Interpret a numerical name as an address. + */ + if (hostaddr_to_sockaddr(host, (char *) 0, 0, &res0) == 0) { + if (strchr((char *) proto_family_list, res0->ai_family) != 0) { + if ((addr = dns_sa_to_rr(host, pref, res0->ai_addr)) == 0) + msg_fatal("host %s: conversion error for address family " + "%d: %m", host, res0->ai_addr->sa_family); + addr_list = dns_rr_append(addr_list, addr); + freeaddrinfo(res0); + return (addr_list); + } + freeaddrinfo(res0); + } + + /* + * Use DNS lookup, but keep the option open to use native name service. + * + * XXX A soft error dominates past and future hard errors. Therefore we + * should not clobber a soft error text and status code. + */ + if (smtp_host_lookup_mask & SMTP_HOST_FLAG_DNS) { + res_opt |= smtp_dns_res_opt; + switch (dns_lookup_v(host, res_opt, &addr, (VSTRING *) 0, + why->reason, DNS_REQ_FLAG_NONE, + proto_info->dns_atype_list)) { + case DNS_OK: + for (rr = addr; rr; rr = rr->next) + rr->pref = pref; + addr_list = dns_rr_append(addr_list, addr); + return (addr_list); + default: + dsb_status(why, "4.4.3"); + return (addr_list); + case DNS_FAIL: + dsb_status(why, SMTP_HAS_SOFT_DSN(why) ? "4.4.3" : "5.4.3"); + return (addr_list); + case DNS_INVAL: + dsb_status(why, SMTP_HAS_SOFT_DSN(why) ? "4.4.4" : "5.4.4"); + return (addr_list); + case DNS_POLICY: + dsb_status(why, "4.7.0"); + return (addr_list); + case DNS_NOTFOUND: + dsb_status(why, SMTP_HAS_SOFT_DSN(why) ? "4.4.4" : "5.4.4"); + /* maybe native naming service will succeed */ + break; + } + } + + /* + * Use the native name service which also looks in /etc/hosts. + * + * XXX A soft error dominates past and future hard errors. Therefore we + * should not clobber a soft error text and status code. + */ +#define RETRY_AI_ERROR(e) \ + ((e) == EAI_AGAIN || (e) == EAI_MEMORY || (e) == EAI_SYSTEM) +#ifdef EAI_NODATA +#define DSN_NOHOST(e) \ + ((e) == EAI_AGAIN || (e) == EAI_NODATA || (e) == EAI_NONAME) +#else +#define DSN_NOHOST(e) \ + ((e) == EAI_AGAIN || (e) == EAI_NONAME) +#endif + + if (smtp_host_lookup_mask & SMTP_HOST_FLAG_NATIVE) { + if ((aierr = hostname_to_sockaddr(host, (char *) 0, 0, &res0)) != 0) { + dsb_simple(why, (SMTP_HAS_SOFT_DSN(why) || RETRY_AI_ERROR(aierr)) ? + (DSN_NOHOST(aierr) ? "4.4.4" : "4.3.0") : + (DSN_NOHOST(aierr) ? "5.4.4" : "5.3.0"), + "unable to look up host %s: %s", + host, MAI_STRERROR(aierr)); + } else { + for (found = 0, res = res0; res != 0; res = res->ai_next) { + if (strchr((char *) proto_family_list, res->ai_family) == 0) { + msg_info("skipping address family %d for host %s", + res->ai_family, host); + continue; + } + found++; + if ((addr = dns_sa_to_rr(host, pref, res->ai_addr)) == 0) + msg_fatal("host %s: conversion error for address family " + "%d: %m", host, res0->ai_addr->sa_family); + addr_list = dns_rr_append(addr_list, addr); + } + freeaddrinfo(res0); + if (found == 0) { + dsb_simple(why, SMTP_HAS_SOFT_DSN(why) ? "4.4.4" : "5.4.4", + "%s: host not found", host); + } + return (addr_list); + } + } + + /* + * No further alternatives for host lookup. + */ + return (addr_list); +} + +/* smtp_addr_list - address lookup for a list of mail exchangers */ + +static DNS_RR *smtp_addr_list(DNS_RR *mx_names, DSN_BUF *why) +{ + DNS_RR *addr_list = 0; + DNS_RR *rr; + int res_opt = 0; + + if (mx_names->dnssec_valid) + res_opt = RES_USE_DNSSEC; +#ifdef USE_TLS + else if (smtp_tls_insecure_mx_policy > TLS_LEV_MAY) + res_opt = RES_USE_DNSSEC; +#endif + + /* + * As long as we are able to look up any host address, we ignore problems + * with DNS lookups (except if we're backup MX, and all the better MX + * hosts can't be found). + * + * XXX 2821: update the error status (0->FAIL upon unrecoverable lookup + * error, any->RETRY upon temporary lookup error) so that we can + * correctly handle the case of no resolvable MX host. Currently this is + * always treated as a soft error. RFC 2821 wants a more precise + * response. + * + * XXX dns_lookup() enables RES_DEFNAMES. This is wrong for names found in + * MX records - we should not append the local domain to dot-less names. + * + * XXX However, this is not the only problem. If we use the native name + * service for host lookup, then it will usually enable RES_DNSRCH which + * appends local domain information to all lookups. In particular, + * getaddrinfo() may invoke a resolver that runs in a different process + * (NIS server, nscd), so we can't even reliably turn this off by + * tweaking the in-process resolver flags. + */ + for (rr = mx_names; rr; rr = rr->next) { + if (rr->type != T_MX) + msg_panic("smtp_addr_list: bad resource type: %d", rr->type); + addr_list = smtp_addr_one(addr_list, (char *) rr->data, res_opt, + rr->pref, why); + } + return (addr_list); +} + +/* smtp_find_self - spot myself in a crowd of mail exchangers */ + +static DNS_RR *smtp_find_self(DNS_RR *addr_list) +{ + const char *myname = "smtp_find_self"; + INET_ADDR_LIST *self; + INET_ADDR_LIST *proxy; + DNS_RR *addr; + int i; + + self = own_inet_addr_list(); + proxy = proxy_inet_addr_list(); + + for (addr = addr_list; addr; addr = addr->next) { + + /* + * Find out if this mail system is listening on this address. + */ + for (i = 0; i < self->used; i++) + if (DNS_RR_EQ_SA(addr, (struct sockaddr *) (self->addrs + i))) { + if (msg_verbose) + msg_info("%s: found self at pref %d", myname, addr->pref); + return (addr); + } + + /* + * Find out if this mail system has a proxy listening on this + * address. + */ + for (i = 0; i < proxy->used; i++) + if (DNS_RR_EQ_SA(addr, (struct sockaddr *) (proxy->addrs + i))) { + if (msg_verbose) + msg_info("%s: found proxy at pref %d", myname, addr->pref); + return (addr); + } + } + + /* + * Didn't find myself, or my proxy. + */ + if (msg_verbose) + msg_info("%s: not found", myname); + return (0); +} + +/* smtp_truncate_self - truncate address list at self and equivalents */ + +static DNS_RR *smtp_truncate_self(DNS_RR *addr_list, unsigned pref) +{ + DNS_RR *addr; + DNS_RR *last; + + for (last = 0, addr = addr_list; addr; last = addr, addr = addr->next) { + if (pref == addr->pref) { + if (msg_verbose) + smtp_print_addr("truncated", addr); + dns_rr_free(addr); + if (last == 0) { + addr_list = 0; + } else { + last->next = 0; + } + break; + } + } + return (addr_list); +} + +/* smtp_balance_inet_proto - balance IPv4/6 protocols within address limit */ + +static DNS_RR *smtp_balance_inet_proto(DNS_RR *addr_list, int misc_flags, + int addr_limit) +{ + const char myname[] = "smtp_balance_inet_proto"; + DNS_RR *rr; + DNS_RR *stripped_list; + DNS_RR *next; + int v6_count; + int v4_count; + int v6_target, + v4_target; + int *p; + + /* + * Precondition: the input is sorted by MX preference (not necessarily IP + * address family preference), and addresses with the same or worse + * preference than 'myself' have been eliminated. Postcondition: the + * relative list order is unchanged, but some elements are removed. + */ + + /* + * Count the number of IPv6 and IPv4 addresses. + */ + for (v4_count = v6_count = 0, rr = addr_list; rr != 0; rr = rr->next) { + if (rr->type == T_A) { + v4_count++; + } else if (rr->type == T_AAAA) { + v6_count++; + } else { + msg_panic("%s: unexpected record type: %s", + myname, dns_strtype(rr->type)); + } + } + + /* + * Ensure that one address type will not out-crowd the other, while + * enforcing the address count limit. This works around a current problem + * where some destination announces primarily IPv6 MX addresses, the + * smtp_address_limit eliminates most or all IPv4 addresses, and the + * destination is not reachable over IPv6. + * + * Maybe: do all smtp_mx_address_limit enforcement here, and remove + * pre-existing enforcement elsewhere. That would obsolete the + * smtp_balance_inet_protocols configuration parameter. + */ + if (v4_count > 0 && v6_count > 0 && v4_count + v6_count > addr_limit) { + + /*- + * Decide how many IPv6 and IPv4 addresses to keep. The code below + * has three branches, corresponding to the regions R1, R2 and R3 + * in the figure. + * + * L = addr_limit + * X = excluded by condition (v4_count + v6_count > addr_limit) + * + * v4_count + * ^ + * | + * L \ R1 + * |X\ | + * |XXX\ | + * |XXXXX\ | R2 + * L/2 +-------\------- + * |XXXXXXX|X\ + * |XXXXXXX|XXX\ R3 + * |XXXXXXX|XXXXX\ + * 0 +-------+-------\--> v6_count + * 0 L/2 L + */ + if (v6_count <= addr_limit / 2) { /* Region R1 */ + v6_target = v6_count; + v4_target = addr_limit - v6_target; + } else if (v4_count <= addr_limit / 2) {/* Region R3 */ + v4_target = v4_count; + v6_target = addr_limit - v4_target; + } else { /* Region R2 */ + /* v4_count > addr_limit / 2 && v6_count > addr_limit / 2 */ + v4_target = (addr_limit + (addr_list->type == T_A)) / 2; + v6_target = addr_limit - v4_target; + } + if (msg_verbose) + msg_info("v6_target=%d, v4_target=%d", v6_target, v4_target); + + /* Enforce the address count targets. */ + stripped_list = 0; + for (rr = addr_list; rr != 0; rr = next) { + next = rr->next; + rr->next = 0; + if (rr->type == T_A) { + p = &v4_target; + } else if (rr->type == T_AAAA) { + p = &v6_target; + } else { + msg_panic("%s: unexpected record type: %s", + myname, dns_strtype(rr->type)); + } + if (*p > 0) { + stripped_list = dns_rr_append(stripped_list, rr); + *p -= 1; + } else { + dns_rr_free(rr); + } + } + if (v4_target > 0 || v6_target > 0) + msg_panic("%s: bad target count: v4_target=%d, v6_target=%d", + myname, v4_target, v6_target); + if (msg_verbose) + smtp_print_addr("smtp_balance_inet_proto result", stripped_list); + return (stripped_list); + } else { + return (addr_list); + } +} + +/* smtp_domain_addr - mail exchanger address lookup */ + +DNS_RR *smtp_domain_addr(const char *name, DNS_RR **mxrr, int misc_flags, + DSN_BUF *why, int *found_myself) +{ + DNS_RR *mx_names; + DNS_RR *addr_list = 0; + DNS_RR *self = 0; + unsigned best_pref; + unsigned best_found; + int r = 0; /* Resolver flags */ + const char *aname; + + dsb_reset(why); /* Paranoia */ + + /* + * Preferences from DNS use 0..32767, fall-backs use 32768+. + */ +#define IMPOSSIBLE_PREFERENCE (~0) + + /* + * Sanity check. + */ + if (smtp_dns_support == SMTP_DNS_DISABLED) + msg_panic("smtp_domain_addr: DNS lookup is disabled"); + if (smtp_dns_support == SMTP_DNS_DNSSEC) + r |= RES_USE_DNSSEC; + + /* + * IDNA support. + */ +#ifndef NO_EAI + if (!allascii(name) && (aname = midna_domain_to_ascii(name)) != 0) { + if (msg_verbose) + msg_info("%s asciified to %s", name, aname); + } else +#endif + aname = name; + + /* + * Look up the mail exchanger hosts listed for this name. Sort the + * results by preference. Look up the corresponding host addresses, and + * truncate the list so that it contains only hosts that are more + * preferred than myself. When no MX resource records exist, look up the + * addresses listed for this name. + * + * According to RFC 974: "It is possible that the list of MXs in the + * response to the query will be empty. This is a special case. If the + * list is empty, mailers should treat it as if it contained one RR, an + * MX RR with a preference value of 0, and a host name of REMOTE. (I.e., + * REMOTE is its only MX). In addition, the mailer should do no further + * processing on the list, but should attempt to deliver the message to + * REMOTE." + * + * Normally it is OK if an MX host cannot be found in the DNS; we'll just + * use a backup one, and silently ignore the better MX host. However, if + * the best backup that we can find in the DNS is the local machine, then + * we must remember that the local machine is not the primary MX host, or + * else we will claim that mail loops back. + * + * XXX Optionally do A lookups even when the MX lookup didn't complete. + * Unfortunately with some DNS servers this is not a transient problem. + * + * XXX Ideally we would perform A lookups only as far as needed. But as long + * as we're looking up all the hosts, it would be better to look up the + * least preferred host first, so that DNS lookup error messages make + * more sense. + * + * XXX 2821: RFC 2821 says that the sender must shuffle equal-preference MX + * hosts, whereas multiple A records per hostname must be used in the + * order as received. They make the bogus assumption that a hostname with + * multiple A records corresponds to one machine with multiple network + * interfaces. + * + * XXX 2821: Postfix recognizes the local machine by looking for its own IP + * address in the list of mail exchangers. RFC 2821 says one has to look + * at the mail exchanger hostname as well, making the bogus assumption + * that an IP address is listed only under one hostname. However, looking + * at hostnames provides a partial solution for MX hosts behind a NAT + * gateway. + */ + switch (dns_lookup(aname, T_MX, r, &mx_names, (VSTRING *) 0, why->reason)) { + default: + dsb_status(why, "4.4.3"); + if (var_ign_mx_lookup_err) + addr_list = smtp_host_addr(aname, misc_flags, why); + break; + case DNS_INVAL: + dsb_status(why, "5.4.4"); + if (var_ign_mx_lookup_err) + addr_list = smtp_host_addr(aname, misc_flags, why); + break; + case DNS_NULLMX: + dsb_status(why, "5.1.0"); + break; + case DNS_POLICY: + dsb_status(why, "4.7.0"); + break; + case DNS_FAIL: + dsb_status(why, "5.4.3"); + if (var_ign_mx_lookup_err) + addr_list = smtp_host_addr(aname, misc_flags, why); + break; + case DNS_OK: + mx_names = dns_rr_sort(mx_names, dns_rr_compare_pref_any); + best_pref = (mx_names ? mx_names->pref : IMPOSSIBLE_PREFERENCE); + addr_list = smtp_addr_list(mx_names, why); + if (mxrr) + *mxrr = dns_rr_copy(mx_names); /* copies one record! */ + dns_rr_free(mx_names); + if (addr_list == 0) { + /* Text does not change. */ + if (var_smtp_defer_mxaddr) { + /* Don't clobber the null terminator. */ + if (SMTP_HAS_HARD_DSN(why)) + SMTP_SET_SOFT_DSN(why); /* XXX */ + /* Require some error status. */ + else if (!SMTP_HAS_SOFT_DSN(why)) + msg_panic("smtp_domain_addr: bad status"); + } + msg_warn("no MX host for %s has a valid address record", name); + break; + } + best_found = (addr_list ? addr_list->pref : IMPOSSIBLE_PREFERENCE); + if (msg_verbose) + smtp_print_addr(name, addr_list); + if ((misc_flags & SMTP_MISC_FLAG_LOOP_DETECT) + && (self = smtp_find_self(addr_list)) != 0) { + addr_list = smtp_truncate_self(addr_list, self->pref); + if (addr_list == 0) { + if (best_pref != best_found) { + dsb_simple(why, "4.4.4", + "unable to find primary relay for %s", name); + } else { + dsb_simple(why, "5.4.6", "mail for %s loops back to myself", + name); + } + } + } +#define SMTP_COMPARE_ADDR(flags) \ + (((flags) & SMTP_MISC_FLAG_PREF_IPV6) ? dns_rr_compare_pref_ipv6 : \ + ((flags) & SMTP_MISC_FLAG_PREF_IPV4) ? dns_rr_compare_pref_ipv4 : \ + dns_rr_compare_pref_any) + + if (addr_list && addr_list->next) { + if (var_smtp_rand_addr) + addr_list = dns_rr_shuffle(addr_list); + addr_list = dns_rr_sort(addr_list, SMTP_COMPARE_ADDR(misc_flags)); + if (var_smtp_mxaddr_limit > 0 && var_smtp_balance_inet_proto) + addr_list = smtp_balance_inet_proto(addr_list, misc_flags, + var_smtp_mxaddr_limit); + } + break; + case DNS_NOTFOUND: + addr_list = smtp_host_addr(aname, misc_flags, why); + break; + } + + /* + * Clean up. + */ + *found_myself |= (self != 0); + return (addr_list); +} + +/* smtp_host_addr - direct host lookup */ + +DNS_RR *smtp_host_addr(const char *host, int misc_flags, DSN_BUF *why) +{ + DNS_RR *addr_list; + int res_opt = 0; + const char *ahost; + + dsb_reset(why); /* Paranoia */ + + if (smtp_dns_support == SMTP_DNS_DNSSEC) + res_opt |= RES_USE_DNSSEC; + + /* + * IDNA support. + */ +#ifndef NO_EAI + if (!allascii(host) && (ahost = midna_domain_to_ascii(host)) != 0) { + if (msg_verbose) + msg_info("%s asciified to %s", host, ahost); + } else +#endif + ahost = host; + + /* + * If the host is specified by numerical address, just convert the + * address to internal form. Otherwise, the host is specified by name. + */ +#define PREF0 0 + addr_list = smtp_addr_one((DNS_RR *) 0, ahost, res_opt, PREF0, why); + if (addr_list + && (misc_flags & SMTP_MISC_FLAG_LOOP_DETECT) + && smtp_find_self(addr_list) != 0) { + dns_rr_free(addr_list); + dsb_simple(why, "5.4.6", "mail for %s loops back to myself", host); + return (0); + } + if (addr_list && addr_list->next) { + if (var_smtp_rand_addr) + addr_list = dns_rr_shuffle(addr_list); + /* The following changes the order of equal-preference hosts. */ + if (inet_proto_info()->ai_family_list[1] != 0) + addr_list = dns_rr_sort(addr_list, SMTP_COMPARE_ADDR(misc_flags)); + if (var_smtp_mxaddr_limit > 0 && var_smtp_balance_inet_proto) + addr_list = smtp_balance_inet_proto(addr_list, misc_flags, + var_smtp_mxaddr_limit); + } + if (msg_verbose) + smtp_print_addr(host, addr_list); + return (addr_list); +} |