diff options
Diffstat (limited to '')
| -rw-r--r-- | src/dns.c | 1332 |
1 files changed, 1332 insertions, 0 deletions
diff --git a/src/dns.c b/src/dns.c new file mode 100644 index 0000000..7d7ee0c --- /dev/null +++ b/src/dns.c @@ -0,0 +1,1332 @@ +/************************************************* +* Exim - an Internet mail transport agent * +*************************************************/ + +/* Copyright (c) The Exim Maintainers 2020 - 2022 */ +/* Copyright (c) University of Cambridge 1995 - 2018 */ +/* See the file NOTICE for conditions of use and distribution. */ + +/* Functions for interfacing with the DNS. */ + +#include "exim.h" + + +/************************************************* +* Fake DNS resolver * +*************************************************/ + +/* This function is called instead of res_search() when Exim is running in its +test harness. It recognizes some special domain names, and uses them to force +failure and retry responses (optionally with a delay). Otherwise, it calls an +external utility that mocks-up a nameserver, if it can find the utility. +If not, it passes its arguments on to res_search(). The fake nameserver may +also return a code specifying that the name should be passed on. + +Background: the original test suite required a real nameserver to carry the +test zones, whereas the new test suite has the fake server for portability. This +code supports both. + +Arguments: + domain the domain name + type the DNS record type + answerptr where to put the answer + size size of the answer area + +Returns: length of returned data, or -1 on error (h_errno set) +*/ + +static int +fakens_search(const uschar *domain, int type, uschar *answerptr, int size) +{ +int len = Ustrlen(domain); +int asize = size; /* Locally modified */ +uschar * name; +uschar utilname[256]; +uschar *aptr = answerptr; /* Locally modified */ +struct stat statbuf; + +/* Remove terminating dot. */ + +if (domain[len - 1] == '.') len--; +name = string_copyn(domain, len); + +/* Look for the fakens utility, and if it exists, call it. */ + +(void)string_format(utilname, sizeof(utilname), "%s/bin/fakens", + config_main_directory); + +if (stat(CS utilname, &statbuf) >= 0) + { + pid_t pid; + int infd, outfd, rc; + uschar *argv[5]; + + DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) using fakens\n", + name, dns_text_type(type)); + + argv[0] = utilname; + argv[1] = config_main_directory; + argv[2] = name; + argv[3] = dns_text_type(type); + argv[4] = NULL; + + pid = child_open(argv, NULL, 0000, &infd, &outfd, FALSE, US"fakens-search"); + if (pid < 0) + log_write(0, LOG_MAIN|LOG_PANIC_DIE, "failed to run fakens: %s", + strerror(errno)); + + len = 0; + rc = -1; + while (asize > 0 && (rc = read(outfd, aptr, asize)) > 0) + { + len += rc; + aptr += rc; /* Don't modify the actual arguments, because they */ + asize -= rc; /* may need to be passed on to res_search(). */ + } + + /* If we ran out of output buffer before exhausting the return, + carry on reading and counting it. */ + + if (asize == 0) + while ((rc = read(outfd, name, sizeof(name))) > 0) + len += rc; + + if (rc < 0) + log_write(0, LOG_MAIN|LOG_PANIC_DIE, "read from fakens failed: %s", + strerror(errno)); + + switch(child_close(pid, 0)) + { + case 0: return len; + case 1: h_errno = HOST_NOT_FOUND; return -1; + case 2: h_errno = TRY_AGAIN; return -1; + default: + case 3: h_errno = NO_RECOVERY; return -1; + case 4: h_errno = NO_DATA; return -1; + case 5: /* Pass on to res_search() */ + DEBUG(D_dns) debug_printf("fakens returned PASS_ON\n"); + } + } +else + { + DEBUG(D_dns) debug_printf("fakens (%s) not found\n", utilname); + } + +/* fakens utility not found, or it returned "pass on" */ + +DEBUG(D_dns) debug_printf("passing %s on to res_search()\n", domain); + +return res_search(CS domain, C_IN, type, answerptr, size); +} + + + +/************************************************* +* Initialize and configure resolver * +*************************************************/ + +/* Initialize the resolver and the storage for holding DNS answers if this is +the first time we have been here, and set the resolver options. + +Arguments: + qualify_single TRUE to set the RES_DEFNAMES option + search_parents TRUE to set the RES_DNSRCH option + use_dnssec TRUE to set the RES_USE_DNSSEC option + +Returns: nothing +*/ + +void +dns_init(BOOL qualify_single, BOOL search_parents, BOOL use_dnssec) +{ +res_state resp = os_get_dns_resolver_res(); + +if ((resp->options & RES_INIT) == 0) + { + DEBUG(D_resolver) resp->options |= RES_DEBUG; /* For Cygwin */ + os_put_dns_resolver_res(resp); + res_init(); + DEBUG(D_resolver) resp->options |= RES_DEBUG; + os_put_dns_resolver_res(resp); + } + +resp->options &= ~(RES_DNSRCH | RES_DEFNAMES); +resp->options |= (qualify_single? RES_DEFNAMES : 0) | + (search_parents? RES_DNSRCH : 0); +if (dns_retrans > 0) resp->retrans = dns_retrans; +if (dns_retry > 0) resp->retry = dns_retry; + +#ifdef RES_USE_EDNS0 +if (dns_use_edns0 >= 0) + { + if (dns_use_edns0) + resp->options |= RES_USE_EDNS0; + else + resp->options &= ~RES_USE_EDNS0; + DEBUG(D_resolver) + debug_printf("Coerced resolver EDNS0 support %s.\n", + dns_use_edns0 ? "on" : "off"); + } +#else +if (dns_use_edns0 >= 0) + DEBUG(D_resolver) + debug_printf("Unable to %sset EDNS0 without resolver support.\n", + dns_use_edns0 ? "" : "un"); +#endif + +#ifndef DISABLE_DNSSEC +# ifdef RES_USE_DNSSEC +# ifndef RES_USE_EDNS0 +# error Have RES_USE_DNSSEC but not RES_USE_EDNS0? Something hinky ... +# endif +if (use_dnssec) + resp->options |= RES_USE_DNSSEC; +if (dns_dnssec_ok >= 0) + { + if (dns_use_edns0 == 0 && dns_dnssec_ok != 0) + { + DEBUG(D_resolver) + debug_printf("CONFLICT: dns_use_edns0 forced false, dns_dnssec_ok forced true, ignoring latter!\n"); + } + else + { + if (dns_dnssec_ok) + resp->options |= RES_USE_DNSSEC; + else + resp->options &= ~RES_USE_DNSSEC; + DEBUG(D_resolver) debug_printf("Coerced resolver DNSSEC support %s.\n", + dns_dnssec_ok ? "on" : "off"); + } + } +# else +if (dns_dnssec_ok >= 0) + DEBUG(D_resolver) + debug_printf("Unable to %sset DNSSEC without resolver support.\n", + dns_dnssec_ok ? "" : "un"); +if (use_dnssec) + DEBUG(D_resolver) + debug_printf("Unable to set DNSSEC without resolver support.\n"); +# endif +#endif /* DISABLE_DNSSEC */ + +os_put_dns_resolver_res(resp); +} + + + +/************************************************* +* Build key name for PTR records * +*************************************************/ + +/* This function inverts an IP address and adds the relevant domain, to produce +a name that can be used to look up PTR records. + +Arguments: + string the IP address as a string + +Returns: an allocated string +*/ + +uschar * +dns_build_reverse(const uschar * string) +{ +const uschar * p = string + Ustrlen(string); +gstring * g = NULL; + +/* Handle IPv4 address */ + +#if HAVE_IPV6 +if (Ustrchr(string, ':') == NULL) +#endif + { + for (int i = 0; i < 4; i++) + { + const uschar * ppp = p; + while (ppp > string && ppp[-1] != '.') ppp--; + g = string_catn(g, ppp, p - ppp); + g = string_catn(g, US".", 1); + p = ppp - 1; + } + g = string_catn(g, US"in-addr.arpa", 12); + } + +/* Handle IPv6 address; convert to binary so as to fill out any +abbreviation in the textual form. */ + +#if HAVE_IPV6 +else + { + int v6[4]; + + g = string_get_tainted(32, string); + (void)host_aton(string, v6); + + /* The original specification for IPv6 reverse lookup was to invert each + nibble, and look in the ip6.int domain. The domain was subsequently + changed to ip6.arpa. */ + + for (int i = 3; i >= 0; i--) + for (int j = 0; j < 32; j += 4) + g = string_fmt_append(g, "%x.", (v6[i] >> j) & 15); + g = string_catn(g, US"ip6.arpa.", 9); + + /* Another way of doing IPv6 reverse lookups was proposed in conjunction + with A6 records. However, it fell out of favour when they did. The + alternative was to construct a binary key, and look in ip6.arpa. I tried + to make this code do that, but I could not make it work on Solaris 8. The + resolver seems to lose the initial backslash somehow. However, now that + this style of reverse lookup has been dropped, it doesn't matter. These + lines are left here purely for historical interest. */ + + /************************************************** + Ustrcpy(pp, "\\[x"); + pp += 3; + + for (int i = 0; i < 4; i++) + { + sprintf(pp, "%08X", v6[i]); + pp += 8; + } + Ustrcpy(pp, US"].ip6.arpa."); + **************************************************/ + + } +#endif +return string_from_gstring(g); +} + + + + +/* Increment the aptr in dnss, checking against dnsa length. +Return: TRUE for a bad result +*/ +static BOOL +dnss_inc_aptr(const dns_answer * dnsa, dns_scan * dnss, unsigned delta) +{ +return (dnss->aptr += delta) >= dnsa->answer + dnsa->answerlen; +} + +/************************************************* +* Get next DNS record from answer block * +*************************************************/ + +/* Call this with reset == RESET_ANSWERS to scan the answer block, reset == +RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to +scan the additional records, and reset == RESET_NEXT to get the next record. +The result is in static storage which must be copied if it is to be preserved. + +Arguments: + dnsa pointer to dns answer block + dnss pointer to dns scan block + reset option specifying what portion to scan, as described above + +Returns: next dns record, or NULL when no more +*/ + +dns_record * +dns_next_rr(const dns_answer *dnsa, dns_scan *dnss, int reset) +{ +const HEADER * h = (const HEADER *)dnsa->answer; +int namelen; + +char * trace = NULL; +#ifdef rr_trace +# define TRACE DEBUG(D_dns) +#else +# define TRACE if (FALSE) +#endif + +/* Reset the saved data when requested to, and skip to the first required RR */ + +if (reset != RESET_NEXT) + { + dnss->rrcount = ntohs(h->qdcount); + TRACE debug_printf("%s: reset (Q rrcount %d)\n", __FUNCTION__, dnss->rrcount); + dnss->aptr = dnsa->answer + sizeof(HEADER); + + /* Skip over questions; failure to expand the name just gives up */ + + while (dnss->rrcount-- > 0) + { + TRACE trace = "Q-namelen"; + namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, + dnss->aptr, (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME); + if (namelen < 0) goto null_return; + /* skip name & type & class */ + TRACE trace = "Q-skip"; + if (dnss_inc_aptr(dnsa, dnss, namelen+4)) goto null_return; + } + + /* Get the number of answer records. */ + + dnss->rrcount = ntohs(h->ancount); + TRACE debug_printf("%s: reset (A rrcount %d)\n", __FUNCTION__, dnss->rrcount); + + /* Skip over answers if we want to look at the authority section. Also skip + the NS records (i.e. authority section) if wanting to look at the additional + records. */ + + if (reset == RESET_ADDITIONAL) + { + TRACE debug_printf("%s: additional\n", __FUNCTION__); + dnss->rrcount += ntohs(h->nscount); + TRACE debug_printf("%s: reset (NS rrcount %d)\n", __FUNCTION__, dnss->rrcount); + } + + if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL) + { + TRACE if (reset == RESET_AUTHORITY) + debug_printf("%s: authority\n", __FUNCTION__); + while (dnss->rrcount-- > 0) + { + TRACE trace = "A-namelen"; + namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, + dnss->aptr, (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME); + if (namelen < 0) goto null_return; + /* skip name, type, class & TTL */ + TRACE trace = "A-hdr"; + if (dnss_inc_aptr(dnsa, dnss, namelen+8)) goto null_return; + GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */ + /* skip over it */ + TRACE trace = "A-skip"; + if (dnss_inc_aptr(dnsa, dnss, dnss->srr.size)) goto null_return; + } + dnss->rrcount = reset == RESET_AUTHORITY + ? ntohs(h->nscount) : ntohs(h->arcount); + TRACE debug_printf("%s: reset (%s rrcount %d)\n", __FUNCTION__, + reset == RESET_AUTHORITY ? "NS" : "AR", dnss->rrcount); + } + TRACE debug_printf("%s: %d RRs to read\n", __FUNCTION__, dnss->rrcount); + } +else + TRACE debug_printf("%s: next (%d left)\n", __FUNCTION__, dnss->rrcount); + +/* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount +contains the number of RR records left. */ + +if (dnss->rrcount-- <= 0) return NULL; + +/* If expanding the RR domain name fails, behave as if no more records +(something safe). */ + +TRACE trace = "R-namelen"; +namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr, + (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME); +if (namelen < 0) goto null_return; + +/* Move the pointer past the name and fill in the rest of the data structure +from the following bytes. */ + +TRACE trace = "R-name"; +if (dnss_inc_aptr(dnsa, dnss, namelen)) goto null_return; + +GETSHORT(dnss->srr.type, dnss->aptr); /* Record type */ +TRACE trace = "R-class"; +if (dnss_inc_aptr(dnsa, dnss, 2)) goto null_return; /* Don't want class */ +GETLONG(dnss->srr.ttl, dnss->aptr); /* TTL */ +GETSHORT(dnss->srr.size, dnss->aptr); /* Size of data portion */ +dnss->srr.data = dnss->aptr; /* The record's data follows */ + +/* Unchecked increment ok here since no further access on this iteration; +will be checked on next at "R-name". */ + +dnss->aptr += dnss->srr.size; /* Advance to next RR */ + +/* Return a pointer to the dns_record structure within the dns_answer. This is +for convenience so that the scans can use nice-looking for loops. */ + +TRACE debug_printf("%s: return %s\n", __FUNCTION__, dns_text_type(dnss->srr.type)); +return &dnss->srr; + +null_return: + TRACE debug_printf("%s: terminate (%d RRs left). Last op: %s; errno %d %s\n", + __FUNCTION__, dnss->rrcount, trace, errno, strerror(errno)); + dnss->rrcount = 0; + return NULL; +} + + +/* Extract the AUTHORITY information from the answer. If the answer isn't +authoritative (AA not set), we do not extract anything. + +The AUTHORITY section contains NS records if the name in question was found, +it contains a SOA record otherwise. (This is just from experience and some +tests, is there some spec?) + +Scan the whole AUTHORITY section, since it may contain other records +(e.g. NSEC3) too. + +Return: name for the authority, in an allocated string, or NULL if none found */ + +static const uschar * +dns_extract_auth_name(const dns_answer * dnsa) /* FIXME: const dns_answer */ +{ +dns_scan dnss; +const HEADER * h = (const HEADER *) dnsa->answer; + +if (h->nscount && h->aa) + for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY); + rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) + if (rr->type == (h->ancount ? T_NS : T_SOA)) + return string_copy(rr->name); +return NULL; +} + + + + +/************************************************* +* Return whether AD bit set in DNS result * +*************************************************/ + +/* We do not perform DNSSEC work ourselves; if the administrator has installed +a verifying resolver which sets AD as appropriate, though, we'll use that. +(AD = Authentic Data, AA = Authoritative Answer) + +Argument: pointer to dns answer block +Returns: bool indicating presence of AD bit +*/ + +BOOL +dns_is_secure(const dns_answer * dnsa) +{ +#ifdef DISABLE_DNSSEC +DEBUG(D_dns) + debug_printf("DNSSEC support disabled at build-time; dns_is_secure() false\n"); +return FALSE; +#else +const HEADER * h = (const HEADER *) dnsa->answer; +const uschar * auth_name; +const uschar * trusted; + +if (dnsa->answerlen < 0) return FALSE; +/* Beware that newer versions of glibc on Linux will filter out the ad bit +unless their shiny new RES_TRUSTAD bit is set for the resolver. */ +if (h->ad) return TRUE; + +/* If the resolver we ask is authoritative for the domain in question, it may +not set the AD but the AA bit. If we explicitly trust the resolver for that +domain (via a domainlist in dns_trust_aa), we return TRUE to indicate a secure +answer. */ + +if ( !h->aa + || !dns_trust_aa + || !(trusted = expand_string(dns_trust_aa)) + || !*trusted + || !(auth_name = dns_extract_auth_name(dnsa)) + || OK != match_isinlist(auth_name, &trusted, 0, &domainlist_anchor, NULL, + MCL_DOMAIN, TRUE, NULL) + ) + return FALSE; + +DEBUG(D_dns) debug_printf("DNS faked the AD bit " + "(got AA and matched with dns_trust_aa (%s in %s))\n", + auth_name, dns_trust_aa); + +return TRUE; +#endif +} + +static void +dns_set_insecure(dns_answer * dnsa) +{ +#ifndef DISABLE_DNSSEC +HEADER * h = (HEADER *)dnsa->answer; +h->aa = h->ad = 0; +#endif +} + +/************************************************ + * Check whether the AA bit is set * + * We need this to warn if we requested AD * + * from an authoritative server * + ************************************************/ + +BOOL +dns_is_aa(const dns_answer * dnsa) +{ +#ifdef DISABLE_DNSSEC +return FALSE; +#else +return dnsa->answerlen >= 0 && ((const HEADER *)dnsa->answer)->aa; +#endif +} + + + +/************************************************* +* Turn DNS type into text * +*************************************************/ + +/* Turn the coded record type into a string for printing. All those that Exim +uses should be included here. + +Argument: record type +Returns: pointer to string +*/ + +uschar * +dns_text_type(int t) +{ +switch(t) + { + case T_A: return US"A"; + case T_MX: return US"MX"; + case T_AAAA: return US"AAAA"; + case T_A6: return US"A6"; + case T_TXT: return US"TXT"; + case T_SPF: return US"SPF"; + case T_PTR: return US"PTR"; + case T_SOA: return US"SOA"; + case T_SRV: return US"SRV"; + case T_NS: return US"NS"; + case T_CNAME: return US"CNAME"; + case T_TLSA: return US"TLSA"; + default: return US"?"; + } +} + + + +/************************************************* +* Cache a failed DNS lookup result * +*************************************************/ + +static void +dns_fail_tag(uschar * buf, const uschar * name, int dns_type) +{ +res_state resp = os_get_dns_resolver_res(); + +/*XX buf needs to be 255 +1 + (max(typetext) == 5) +1 + max(chars_for_long-max) +1 +We truncate the name here for safety... could use a dynamic string. */ + +sprintf(CS buf, "%.255s-%s-%lx", name, dns_text_type(dns_type), + (unsigned long) resp->options); +} + + +/* We cache failed lookup results so as not to experience timeouts many +times for the same domain. We need to retain the resolver options because they +may change. For successful lookups, we rely on resolver and/or name server +caching. + +Arguments: + name the domain name + type the lookup type + expiry time TTL expires, or zero for unlimited + rc the return code + +Returns: the return code +*/ + +/* we need: 255 +1 + (max(typetext) == 5) +1 + max(chars_for_long-max) +1 */ +#define DNS_FAILTAG_MAX 290 +#define DNS_FAILNODE_SIZE \ + (sizeof(expiring_data) + sizeof(tree_node) + DNS_FAILTAG_MAX) + +static int +dns_fail_return(const uschar * name, int type, time_t expiry, int rc) +{ +uschar node_name[DNS_FAILTAG_MAX]; +tree_node * previous, * new; +expiring_data * e; + +dns_fail_tag(node_name, name, type); +if ((previous = tree_search(tree_dns_fails, node_name))) + e = previous->data.ptr; +else + { + e = store_get_perm(DNS_FAILNODE_SIZE, name); + new = (void *)(e+1); + dns_fail_tag(new->name, name, type); + new->data.ptr = e; + (void)tree_insertnode(&tree_dns_fails, new); + } + +DEBUG(D_dns) debug_printf(" %s neg-cache entry for %s, ttl %d\n", + previous ? "update" : "writing", + node_name, expiry ? (int)(expiry - time(NULL)) : -1); +e->expiry = expiry; +e->data.val = rc; +return rc; +} + + +/* Return the cached result of a known-bad lookup, or -1. +*/ +static int +dns_fail_cache_hit(const uschar * name, int type) +{ +uschar node_name[DNS_FAILTAG_MAX]; +tree_node * previous; +expiring_data * e; +int val, rc; + +dns_fail_tag(node_name, name, type); +if (!(previous = tree_search(tree_dns_fails, node_name))) + return -1; + +e = previous->data.ptr; +val = e->data.val; +rc = e->expiry && e->expiry <= time(NULL) ? -1 : val; + +DEBUG(D_dns) debug_printf("DNS lookup of %.255s (%s): %scached value %s%s\n", + name, dns_text_type(type), + rc == -1 ? "" : "using ", + dns_rc_names[val], + rc == -1 ? " past valid time" : ""); + +return rc; +} + + + +/* This is really gross. The successful return value from res_search() is +the packet length, which is stored in dnsa->answerlen. If we get a +negative DNS reply then res_search() returns -1, which causes the bounds +checks for name decompression to fail when it is treated as a packet +length, which in turn causes the authority search to fail. The correct +packet length has been lost inside libresolv, so we have to guess a +replacement value. (The only way to fix this properly would be to +re-implement res_search() and res_query() so that they don't muddle their +success and packet length return values.) For added safety we only reset +the packet length if the packet header looks plausible. + +Return TRUE iff it seemed ok */ + +static BOOL +fake_dnsa_len_for_fail(dns_answer * dnsa, int type) +{ +const HEADER * h = (const HEADER *)dnsa->answer; + +if ( h->qr == 1 /* a response */ + && h->opcode == QUERY + && h->tc == 0 /* nmessage not truncated */ + && (h->rcode == NOERROR || h->rcode == NXDOMAIN) + && ( ntohs(h->qdcount) == 1 /* one question record */ + || f.running_in_test_harness) + && ntohs(h->ancount) == 0 /* no answer records */ + && ntohs(h->nscount) >= 1) /* authority records */ + { + DEBUG(D_dns) debug_printf("faking res_search(%s) response length as %d\n", + dns_text_type(type), (int)sizeof(dnsa->answer)); + dnsa->answerlen = sizeof(dnsa->answer); + return TRUE; + } +DEBUG(D_dns) debug_printf("DNS: couldn't fake dnsa len\n"); +/* Maybe we should just do a second lookup for an SOA? */ +return FALSE; +} + + +/* Return the TTL suitable for an NXDOMAIN result, which is given +in the SOA. We hope that one was returned in the lookup, and do not +bother doing a separate lookup; if not found return a forever TTL. +*/ + +time_t +dns_expire_from_soa(dns_answer * dnsa, int type) +{ +dns_scan dnss; + +if (fake_dnsa_len_for_fail(dnsa, type)) + for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY); + rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT) + ) if (rr->type == T_SOA) + { + const uschar * p = rr->data; + uschar discard_buf[256]; + int len; + unsigned long ttl; + + /* Skip the mname & rname strings */ + + if ((len = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, + p, (DN_EXPAND_ARG4_TYPE)discard_buf, 256)) < 0) + break; + p += len; + if ((len = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, + p, (DN_EXPAND_ARG4_TYPE)discard_buf, 256)) < 0) + break; + p += len; + + /* Skip the SOA serial, refresh, retry & expire. Grab the TTL */ + + if (p > dnsa->answer + dnsa->answerlen - 5 * INT32SZ) + break; + p += 4 * INT32SZ; + GETLONG(ttl, p); + + return time(NULL) + ttl; + } + +DEBUG(D_dns) debug_printf("DNS: no SOA record found for neg-TTL\n"); +return 0; +} + + +/************************************************* +* Do basic DNS lookup * +*************************************************/ + +/* Call the resolver to look up the given domain name, using the given type, +and check the result. The error code TRY_AGAIN is documented as meaning "non- +Authoritative Host not found, or SERVERFAIL". Sometimes there are badly set +up nameservers that produce this error continually, so there is the option of +providing a list of domains for which this is treated as a non-existent +host. + +The dns_answer structure is pretty big; enough to hold a max-sized DNS message +- so best allocated from fast-release memory. As of writing, all our callers +use a stack-auto variable. + +Arguments: + dnsa pointer to dns_answer structure + name name to look up + type type of DNS record required (T_A, T_MX, etc) + +Returns: DNS_SUCCEED successful lookup + DNS_NOMATCH name not found (NXDOMAIN) + or name contains illegal characters (if checking) + or name is an IP address (for IP address lookup) + DNS_NODATA domain exists, but no data for this type (NODATA) + DNS_AGAIN soft failure, try again later + DNS_FAIL DNS failure +*/ + +int +dns_basic_lookup(dns_answer * dnsa, const uschar * name, int type) +{ +int rc; +#ifndef STAND_ALONE +const uschar * save_domain; +#endif + +/* DNS lookup failures of any kind are cached in a tree. This is mainly so that +a timeout on one domain doesn't happen time and time again for messages that +have many addresses in the same domain. We rely on the resolver and name server +caching for successful lookups. +*/ + +if ((rc = dns_fail_cache_hit(name, type)) > 0) + { + dnsa->answerlen = -1; + return rc; + } + +#ifdef SUPPORT_I18N +/* Convert all names to a-label form before doing lookup */ + { + uschar * alabel; + uschar * errstr = NULL; + DEBUG(D_dns) if (string_is_utf8(name)) + debug_printf("convert utf8 '%s' to alabel for for lookup\n", name); + if ((alabel = string_domain_utf8_to_alabel(name, &errstr)), errstr) + { + DEBUG(D_dns) + debug_printf("DNS name '%s' utf8 conversion to alabel failed: %s\n", name, + errstr); + f.host_find_failed_syntax = TRUE; + return DNS_NOMATCH; + } + name = alabel; + } +#endif + +/* If configured, check the hygiene of the name passed to lookup. Otherwise, +although DNS lookups may give REFUSED at the lower level, some resolvers +turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such +domains cannot be in the DNS. The check is now done by a regular expression; +give it space for substring storage to save it having to get its own if the +regex has substrings that are used - the default uses a conditional. + +This test is omitted for PTR records. These occur only in calls from the dnsdb +lookup, which constructs the names itself, so they should be OK. Besides, +bitstring labels don't conform to normal name syntax. (But they aren't used any +more.) */ + +#ifndef STAND_ALONE /* Omit this for stand-alone tests */ + +if (check_dns_names_pattern[0] != 0 && type != T_PTR && type != T_TXT) + { + dns_pattern_init(); + if (!regex_match(regex_check_dns_names, name, -1, NULL)) + { + DEBUG(D_dns) + debug_printf("DNS name syntax check failed: %s (%s)\n", name, + dns_text_type(type)); + f.host_find_failed_syntax = TRUE; + return DNS_NOMATCH; + } + } + +#endif /* STAND_ALONE */ + +/* Call the resolver; for an overlong response, res_search() will return the +number of bytes the message would need, so we need to check for this case. The +effect is to truncate overlong data. + +On some systems, res_search() will recognize "A-for-A" queries and return +the IP address instead of returning -1 with h_error=HOST_NOT_FOUND. Some +nameservers are also believed to do this. It is, of course, contrary to the +specification of the DNS, so we lock it out. */ + +if ((type == T_A || type == T_AAAA) && string_is_ip_address(name, NULL) != 0) + return DNS_NOMATCH; + +/* If we are running in the test harness, instead of calling the normal resolver +(res_search), we call fakens_search(), which recognizes certain special +domains, and interfaces to a fake nameserver for certain special zones. */ + +h_errno = 0; +dnsa->answerlen = f.running_in_test_harness + ? fakens_search(name, type, dnsa->answer, sizeof(dnsa->answer)) + : res_search(CCS name, C_IN, type, dnsa->answer, sizeof(dnsa->answer)); + +if (dnsa->answerlen > (int) sizeof(dnsa->answer)) + { + DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) resulted in overlong packet" + " (size %d), truncating to %u.\n", + name, dns_text_type(type), dnsa->answerlen, (unsigned int) sizeof(dnsa->answer)); + dnsa->answerlen = sizeof(dnsa->answer); + } + +if (dnsa->answerlen < 0) switch (h_errno) + { + case HOST_NOT_FOUND: + DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n" + "returning DNS_NOMATCH\n", name, dns_text_type(type)); + return dns_fail_return(name, type, dns_expire_from_soa(dnsa, type), DNS_NOMATCH); + + case TRY_AGAIN: + DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n", + name, dns_text_type(type)); + + /* Cut this out for various test programs */ +#ifndef STAND_ALONE + save_domain = deliver_domain; + deliver_domain = string_copy(name); /* set $domain */ + rc = match_isinlist(name, CUSS &dns_again_means_nonexist, 0, + &domainlist_anchor, NULL, MCL_DOMAIN, TRUE, NULL); + deliver_domain = save_domain; + if (rc != OK) + { + DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n"); + return dns_fail_return(name, type, 0, DNS_AGAIN); + } + DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning " + "DNS_NOMATCH\n", name); + return dns_fail_return(name, type, dns_expire_from_soa(dnsa, type), DNS_NOMATCH); + +#else /* For stand-alone tests */ + return dns_fail_return(name, type, 0, DNS_AGAIN); +#endif + + case NO_RECOVERY: + DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n" + "returning DNS_FAIL\n", name, dns_text_type(type)); + return dns_fail_return(name, type, 0, DNS_FAIL); + + case NO_DATA: + DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n" + "returning DNS_NODATA\n", name, dns_text_type(type)); + return dns_fail_return(name, type, dns_expire_from_soa(dnsa, type), DNS_NODATA); + + default: + DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n" + "returning DNS_FAIL\n", name, dns_text_type(type), h_errno); + return dns_fail_return(name, type, 0, DNS_FAIL); + } + +DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n", + name, dns_text_type(type)); + +return DNS_SUCCEED; +} + + + + +/************************************************ +* Do a DNS lookup and handle CNAMES * +************************************************/ + +/* Look up the given domain name, using the given type. Follow CNAMEs if +necessary, but only so many times. There aren't supposed to be CNAME chains in +the DNS, but you are supposed to cope with them if you find them. +By default, follow one CNAME since a resolver has been seen, faced with +an MX request and a CNAME (to an A) but no MX present, returning the CNAME. + +The assumption is made that if the resolver gives back records of the +requested type *and* a CNAME, we don't need to make another call to look up +the CNAME. I can't see how it could return only some of the right records. If +it's done a CNAME lookup in the past, it will have all of them; if not, it +won't return any. + +If fully_qualified_name is not NULL, set it to point to the full name +returned by the resolver, if this is different to what it is given, unless +the returned name starts with "*" as some nameservers seem to be returning +wildcards in this form. In international mode "different" means "alabel +forms are different". + +Arguments: + dnsa pointer to dns_answer structure + name domain name to look up + type DNS record type (T_A, T_MX, etc) + fully_qualified_name if not NULL, return the returned name here if its + contents are different (i.e. it must be preset) + +Returns: DNS_SUCCEED successful lookup + DNS_NOMATCH name not found + DNS_NODATA no data found + DNS_AGAIN soft failure, try again later + DNS_FAIL DNS failure +*/ + +int +dns_lookup(dns_answer *dnsa, const uschar *name, int type, + const uschar **fully_qualified_name) +{ +const uschar *orig_name = name; +BOOL secure_so_far = TRUE; + +/* By default, assume the resolver follows CNAME chains (and returns NODATA for +an unterminated one). If it also does that for a CNAME loop, fine; if it returns +a CNAME (maybe the last?) whine about it. However, retain the coding for dumb +resolvers hiding behind a config variable. Loop to follow CNAME chains so far, +but no further... The testsuite tests the latter case, mostly assuming that the +former will work. */ + +for (int i = 0; i <= dns_cname_loops; i++) + { + uschar * data; + dns_record cname_rr, type_rr; + dns_scan dnss; + int rc; + + /* DNS lookup failures get passed straight back. */ + + if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED) + return rc; + + /* We should have either records of the required type, or a CNAME record, + or both. We need to know whether both exist for getting the fully qualified + name, but avoid scanning more than necessary. Note that we must copy the + contents of any rr blocks returned by dns_next_rr() as they use the same + area in the dnsa block. */ + + cname_rr.data = type_rr.data = NULL; + for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); + rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) + if (rr->type == type) + { + if (type_rr.data == NULL) type_rr = *rr; + if (cname_rr.data != NULL) break; + } + else if (rr->type == T_CNAME) + cname_rr = *rr; + + /* For the first time round this loop, if a CNAME was found, take the fully + qualified name from it; otherwise from the first data record, if present. */ + + if (i == 0 && fully_qualified_name) + { + uschar * rr_name = cname_rr.data + ? cname_rr.name : type_rr.data ? type_rr.name : NULL; + if ( rr_name + && Ustrcmp(rr_name, *fully_qualified_name) != 0 + && rr_name[0] != '*' +#ifdef SUPPORT_I18N + && ( !string_is_utf8(*fully_qualified_name) + || Ustrcmp(rr_name, + string_domain_utf8_to_alabel(*fully_qualified_name, NULL)) != 0 + ) +#endif + ) + *fully_qualified_name = string_copy_dnsdomain(rr_name); + } + + /* If any data records of the correct type were found, we are done. */ + + if (type_rr.data) + { + if (!secure_so_far) /* mark insecure if any element of CNAME chain was */ + dns_set_insecure(dnsa); + return DNS_SUCCEED; + } + + /* If there are no data records, we need to re-scan the DNS using the + domain given in the CNAME record, which should exist (otherwise we should + have had a failure from dns_lookup). However code against the possibility of + its not existing. */ + + if (!cname_rr.data) + return DNS_FAIL; + + /* DNS data comes from the outside, hence tainted */ + data = store_get(256, GET_TAINTED); + if (dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, + cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, 256) < 0) + return DNS_FAIL; + name = data; + + if (!dns_is_secure(dnsa)) + secure_so_far = FALSE; + + DEBUG(D_dns) debug_printf("CNAME found: change to %s\n", name); + } /* Loop back to do another lookup */ + +/*Control reaches here after 10 times round the CNAME loop. Something isn't +right... */ + +log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name); +return DNS_FAIL; +} + + + + + + +/************************************************ +* Do a DNS lookup and handle virtual types * +************************************************/ + +/* This function handles some invented "lookup types" that synthesize features +not available in the basic types. The special types all have negative values. +Positive type values are passed straight on to dns_lookup(). + +Arguments: + dnsa pointer to dns_answer structure + name domain name to look up + type DNS record type (T_A, T_MX, etc or a "special") + fully_qualified_name if not NULL, return the returned name here if its + contents are different (i.e. it must be preset) + +Returns: DNS_SUCCEED successful lookup + DNS_NOMATCH name not found + DNS_NODATA no data found + DNS_AGAIN soft failure, try again later + DNS_FAIL DNS failure +*/ + +int +dns_special_lookup(dns_answer *dnsa, const uschar *name, int type, + const uschar **fully_qualified_name) +{ +switch (type) + { + /* The "mx hosts only" type doesn't require any special action here */ + case T_MXH: + return dns_lookup(dnsa, name, T_MX, fully_qualified_name); + + /* Find nameservers for the domain or the nearest enclosing zone, excluding + the root servers. */ + case T_ZNS: + type = T_NS; + /* FALLTHROUGH */ + case T_SOA: + { + const uschar *d = name; + while (d != 0) + { + int rc = dns_lookup(dnsa, d, type, fully_qualified_name); + if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc; + while (*d != 0 && *d != '.') d++; + if (*d++ == 0) break; + } + return DNS_NOMATCH; + } + + /* Try to look up the Client SMTP Authorization SRV record for the name. If + there isn't one, search from the top downwards for a CSA record in a parent + domain, which might be making assertions about subdomains. If we find a record + we set fully_qualified_name to whichever lookup succeeded, so that the caller + can tell whether to look at the explicit authorization field or the subdomain + assertion field. */ + case T_CSA: + { + uschar *srvname, *namesuff, *tld; + int priority, dummy_weight, port; + int limit, rc, i; + BOOL ipv6; + dns_record *rr; + dns_scan dnss; + + DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name); + + srvname = string_sprintf("_client._smtp.%s", name); + rc = dns_lookup(dnsa, srvname, T_SRV, NULL); + if (rc == DNS_SUCCEED || rc == DNS_AGAIN) + { + if (rc == DNS_SUCCEED) *fully_qualified_name = string_copy(name); + return rc; + } + + /* Search for CSA subdomain assertion SRV records from the top downwards, + starting with the 2nd level domain. This order maximizes cache-friendliness. + We skip the top level domains to avoid loading their nameservers and because + we know they'll never have CSA SRV records. */ + + namesuff = Ustrrchr(name, '.'); + if (namesuff == NULL) return DNS_NOMATCH; + tld = namesuff + 1; + ipv6 = FALSE; + limit = dns_csa_search_limit; + + /* Use more appropriate search parameters if we are in the reverse DNS. */ + + if (strcmpic(namesuff, US".arpa") == 0) + if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0) + { + namesuff -= 8; + tld = namesuff + 1; + limit = 3; + } + else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0) + { + namesuff -= 4; + tld = namesuff + 1; + ipv6 = TRUE; + limit = 3; + } + + DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld); + + /* Do not perform the search if the top level or 2nd level domains do not + exist. This is quite common, and when it occurs all the search queries would + go to the root or TLD name servers, which is not friendly. So we check the + AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then + the TLD or the 2LD (respectively) doesn't exist and we can skip the search. + If the TLD and the 2LD exist but the explicit CSA record lookup failed, then + the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */ + + if (rc == DNS_NOMATCH) return DNS_NOMATCH; + + for (i = 0; i < limit; i++) + { + if (ipv6) + { + /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP + address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */ + namesuff -= 8; + if (namesuff <= name) return DNS_NOMATCH; + } + else + /* Find the start of the preceding domain name label. */ + do + if (--namesuff <= name) return DNS_NOMATCH; + while (*namesuff != '.'); + + DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1); + + srvname = string_sprintf("_client._smtp.%s", namesuff + 1); + rc = dns_lookup(dnsa, srvname, T_SRV, NULL); + if (rc == DNS_AGAIN) return rc; + if (rc != DNS_SUCCEED) continue; + + /* Check that the SRV record we have found is worth returning. We don't + just return the first one we find, because some lower level SRV record + might make stricter assertions than its parent domain. */ + + for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); + rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) if (rr->type == T_SRV) + { + const uschar * p = rr->data; + + /* Extract the numerical SRV fields (p is incremented) */ + GETSHORT(priority, p); + GETSHORT(dummy_weight, p); + GETSHORT(port, p); + + /* Check the CSA version number */ + if (priority != 1) continue; + + /* If it's making an interesting assertion, return this response. */ + if (port & 1) + { + *fully_qualified_name = namesuff + 1; + return DNS_SUCCEED; + } + } + } + return DNS_NOMATCH; + } + + default: + if (type >= 0) + return dns_lookup(dnsa, name, type, fully_qualified_name); + } + +/* Control should never reach here */ + +return DNS_FAIL; +} + + + + + +/************************************************* +* Get address(es) from DNS record * +*************************************************/ + +/* The record type is either T_A for an IPv4 address or T_AAAA for an IPv6 address. + +Argument: + dnsa the DNS answer block + rr the RR + +Returns: pointer to a chain of dns_address items; NULL when the dnsa was overrun +*/ + +dns_address * +dns_address_from_rr(dns_answer *dnsa, dns_record *rr) +{ +dns_address * yield = NULL; +uschar * dnsa_lim = dnsa->answer + dnsa->answerlen; + +if (rr->type == T_A) + { + uschar *p = US rr->data; + if (p + 4 <= dnsa_lim) + { + /* the IP is not regarded as tainted */ + yield = store_get(sizeof(dns_address) + 20, GET_UNTAINTED); + (void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]); + yield->next = NULL; + } + } + +#if HAVE_IPV6 + +else + { + if (rr->data + 16 <= dnsa_lim) + { + struct in6_addr in6; + for (int i = 0; i < 16; i++) in6.s6_addr[i] = rr->data[i]; + yield = store_get(sizeof(dns_address) + 50, GET_UNTAINTED); + inet_ntop(AF_INET6, &in6, CS yield->address, 50); + yield->next = NULL; + } + } +#endif /* HAVE_IPV6 */ + +return yield; +} + + + +void +dns_pattern_init(void) +{ +if (check_dns_names_pattern[0] != 0 && !regex_check_dns_names) + regex_check_dns_names = + regex_must_compile(check_dns_names_pattern, FALSE, TRUE); +} + +/* vi: aw ai sw=2 +*/ +/* End of dns.c */ |