diff options
Diffstat (limited to 'src/smtp/smtp_tls_policy.c')
| -rw-r--r-- | src/smtp/smtp_tls_policy.c | 928 |
1 files changed, 928 insertions, 0 deletions
diff --git a/src/smtp/smtp_tls_policy.c b/src/smtp/smtp_tls_policy.c new file mode 100644 index 0000000..4b394a9 --- /dev/null +++ b/src/smtp/smtp_tls_policy.c @@ -0,0 +1,928 @@ +/*++ +/* NAME +/* smtp_tls_policy 3 +/* SUMMARY +/* SMTP_TLS_POLICY structure management +/* SYNOPSIS +/* #include "smtp.h" +/* +/* void smtp_tls_list_init() +/* +/* int smtp_tls_policy_cache_query(why, tls, iter) +/* DSN_BUF *why; +/* SMTP_TLS_POLICY *tls; +/* SMTP_ITERATOR *iter; +/* +/* void smtp_tls_policy_dummy(tls) +/* SMTP_TLS_POLICY *tls; +/* +/* void smtp_tls_policy_cache_flush() +/* DESCRIPTION +/* smtp_tls_list_init() initializes lookup tables used by the TLS +/* policy engine. +/* +/* smtp_tls_policy_cache_query() returns a shallow copy of the +/* cached SMTP_TLS_POLICY structure for the iterator's +/* destination, host, port and DNSSEC validation status. +/* This copy is guaranteed to be valid until the next +/* smtp_tls_policy_cache_query() or smtp_tls_policy_cache_flush() +/* call. The caller can override the TLS security level without +/* corrupting the policy cache. +/* When any required table or DNS lookups fail, the TLS level +/* is set to TLS_LEV_INVALID, the "why" argument is updated +/* with the error reason and the result value is zero (false). +/* +/* smtp_tls_policy_dummy() initializes a trivial, non-cached, +/* policy with TLS disabled. +/* +/* smtp_tls_policy_cache_flush() destroys the TLS policy cache +/* and contents. +/* +/* Arguments: +/* .IP why +/* A pointer to a DSN_BUF which holds error status information when +/* the TLS policy lookup fails. +/* .IP tls +/* Pointer to TLS policy storage. +/* .IP iter +/* The literal next-hop or fall-back destination including +/* the optional [] and including the :port or :service; +/* the name of the remote host after MX and CNAME expansions +/* (see smtp_cname_overrides_servername for the handling +/* of hostnames that resolve to a CNAME record); +/* the printable address of the remote host; +/* the remote port in network byte order; +/* the DNSSEC validation status of the host name lookup after +/* MX and CNAME expansions. +/* LICENSE +/* .ad +/* .fi +/* This software is free. You can do with it whatever you want. +/* The original author kindly requests that you acknowledge +/* the use of his software. +/* AUTHOR(S) +/* TLS support originally by: +/* Lutz Jaenicke +/* BTU Cottbus +/* Allgemeine Elektrotechnik +/* Universitaetsplatz 3-4 +/* D-03044 Cottbus, Germany +/* +/* Updated by: +/* 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 +/* +/* Viktor Dukhovni +/*--*/ + +/* System library. */ + +#include <sys_defs.h> + +#ifdef USE_TLS + +#include <netinet/in.h> /* ntohs() for Solaris or BSD */ +#include <arpa/inet.h> /* ntohs() for Linux or BSD */ +#include <stdlib.h> +#include <string.h> + +#ifdef STRCASECMP_IN_STRINGS_H +#include <strings.h> +#endif + +/* Utility library. */ + +#include <msg.h> +#include <mymalloc.h> +#include <vstring.h> +#include <stringops.h> +#include <valid_hostname.h> +#include <valid_utf8_hostname.h> +#include <ctable.h> + +/* Global library. */ + +#include <mail_params.h> +#include <maps.h> +#include <dsn_buf.h> + +/* DNS library. */ + +#include <dns.h> + +/* Application-specific. */ + +#include "smtp.h" + +/* XXX Cache size should scale with [sl]mtp_mx_address_limit. */ +#define CACHE_SIZE 20 +static CTABLE *policy_cache; + +static int global_tls_level(void); +static void dane_init(SMTP_TLS_POLICY *, SMTP_ITERATOR *); + +static MAPS *tls_policy; /* lookup table(s) */ +static MAPS *tls_per_site; /* lookup table(s) */ + +/* smtp_tls_list_init - initialize per-site policy lists */ + +void smtp_tls_list_init(void) +{ + if (*var_smtp_tls_policy) { + tls_policy = maps_create(VAR_LMTP_SMTP(TLS_POLICY), + var_smtp_tls_policy, + DICT_FLAG_LOCK | DICT_FLAG_FOLD_FIX + | DICT_FLAG_UTF8_REQUEST); + if (*var_smtp_tls_per_site) + msg_warn("%s ignored when %s is not empty.", + VAR_LMTP_SMTP(TLS_PER_SITE), VAR_LMTP_SMTP(TLS_POLICY)); + return; + } + if (*var_smtp_tls_per_site) { + tls_per_site = maps_create(VAR_LMTP_SMTP(TLS_PER_SITE), + var_smtp_tls_per_site, + DICT_FLAG_LOCK | DICT_FLAG_FOLD_FIX + | DICT_FLAG_UTF8_REQUEST); + } +} + +/* policy_name - printable tls policy level */ + +static const char *policy_name(int tls_level) +{ + const char *name = str_tls_level(tls_level); + + if (name == 0) + name = "unknown"; + return name; +} + +#define MARK_INVALID(why, levelp) do { \ + dsb_simple((why), "4.7.5", "client TLS configuration problem"); \ + *(levelp) = TLS_LEV_INVALID; } while (0) + +/* tls_site_lookup - look up per-site TLS security level */ + +static void tls_site_lookup(SMTP_TLS_POLICY *tls, int *site_level, + const char *site_name, const char *site_class) +{ + const char *lookup; + + /* + * Look up a non-default policy. In case of multiple lookup results, the + * precedence order is a permutation of the TLS enforcement level order: + * VERIFY, ENCRYPT, NONE, MAY, NOTFOUND. I.e. we override MAY with a more + * specific policy including NONE, otherwise we choose the stronger + * enforcement level. + */ + if ((lookup = maps_find(tls_per_site, site_name, 0)) != 0) { + if (!strcasecmp(lookup, "NONE")) { + /* NONE overrides MAY or NOTFOUND. */ + if (*site_level <= TLS_LEV_MAY) + *site_level = TLS_LEV_NONE; + } else if (!strcasecmp(lookup, "MAY")) { + /* MAY overrides NOTFOUND but not NONE. */ + if (*site_level < TLS_LEV_NONE) + *site_level = TLS_LEV_MAY; + } else if (!strcasecmp(lookup, "MUST_NOPEERMATCH")) { + if (*site_level < TLS_LEV_ENCRYPT) + *site_level = TLS_LEV_ENCRYPT; + } else if (!strcasecmp(lookup, "MUST")) { + if (*site_level < TLS_LEV_VERIFY) + *site_level = TLS_LEV_VERIFY; + } else { + msg_warn("%s: unknown TLS policy '%s' for %s %s", + tls_per_site->title, lookup, site_class, site_name); + MARK_INVALID(tls->why, site_level); + return; + } + } else if (tls_per_site->error) { + msg_warn("%s: %s \"%s\": per-site table lookup error", + tls_per_site->title, site_class, site_name); + dsb_simple(tls->why, "4.3.0", "Temporary lookup error"); + *site_level = TLS_LEV_INVALID; + return; + } + return; +} + +/* tls_policy_lookup_one - look up destination TLS policy */ + +static void tls_policy_lookup_one(SMTP_TLS_POLICY *tls, int *site_level, + const char *site_name, + const char *site_class) +{ + const char *lookup; + char *policy; + char *saved_policy; + char *tok; + const char *err; + char *name; + char *val; + static VSTRING *cbuf; + +#undef FREE_RETURN +#define FREE_RETURN do { myfree(saved_policy); return; } while (0) + +#define INVALID_RETURN(why, levelp) do { \ + MARK_INVALID((why), (levelp)); FREE_RETURN; } while (0) + +#define WHERE \ + STR(vstring_sprintf(cbuf, "%s, %s \"%s\"", \ + tls_policy->title, site_class, site_name)) + + if (cbuf == 0) + cbuf = vstring_alloc(10); + + if ((lookup = maps_find(tls_policy, site_name, 0)) == 0) { + if (tls_policy->error) { + msg_warn("%s: policy table lookup error", WHERE); + MARK_INVALID(tls->why, site_level); + } + return; + } + saved_policy = policy = mystrdup(lookup); + + if ((tok = mystrtok(&policy, CHARS_COMMA_SP)) == 0) { + msg_warn("%s: invalid empty policy", WHERE); + INVALID_RETURN(tls->why, site_level); + } + *site_level = tls_level_lookup(tok); + if (*site_level == TLS_LEV_INVALID) { + /* tls_level_lookup() logs no warning. */ + msg_warn("%s: invalid security level \"%s\"", WHERE, tok); + INVALID_RETURN(tls->why, site_level); + } + + /* + * Warn about ignored attributes when TLS is disabled. + */ + if (*site_level < TLS_LEV_MAY) { + while ((tok = mystrtok(&policy, CHARS_COMMA_SP)) != 0) + msg_warn("%s: ignoring attribute \"%s\" with TLS disabled", + WHERE, tok); + FREE_RETURN; + } + + /* + * Errors in attributes may have security consequences, don't ignore + * errors that can degrade security. + */ + while ((tok = mystrtok(&policy, CHARS_COMMA_SP)) != 0) { + if ((err = split_nameval(tok, &name, &val)) != 0) { + msg_warn("%s: malformed attribute/value pair \"%s\": %s", + WHERE, tok, err); + INVALID_RETURN(tls->why, site_level); + } + /* Only one instance per policy. */ + if (!strcasecmp(name, "ciphers")) { + if (*val == 0) { + msg_warn("%s: attribute \"%s\" has empty value", WHERE, name); + INVALID_RETURN(tls->why, site_level); + } + if (tls->grade) { + msg_warn("%s: attribute \"%s\" is specified multiple times", + WHERE, name); + INVALID_RETURN(tls->why, site_level); + } + tls->grade = mystrdup(val); + continue; + } + /* Only one instance per policy. */ + if (!strcasecmp(name, "protocols")) { + if (tls->protocols) { + msg_warn("%s: attribute \"%s\" is specified multiple times", + WHERE, name); + INVALID_RETURN(tls->why, site_level); + } + tls->protocols = mystrdup(val); + continue; + } + /* Only one instance per policy. */ + if (!strcasecmp(name, "servername")) { + if (tls->sni) { + msg_warn("%s: attribute \"%s\" is specified multiple times", + WHERE, name); + INVALID_RETURN(tls->why, site_level); + } + if (valid_hostname(val, DONT_GRIPE)) + tls->sni = mystrdup(val); + else { + msg_warn("%s: \"%s=%s\" specifies an invalid hostname", + WHERE, name, val); + INVALID_RETURN(tls->why, site_level); + } + continue; + } + /* Multiple instances per policy. */ + if (!strcasecmp(name, "match")) { + if (*val == 0) { + msg_warn("%s: attribute \"%s\" has empty value", WHERE, name); + INVALID_RETURN(tls->why, site_level); + } + switch (*site_level) { + default: + msg_warn("%s: attribute \"%s\" invalid at security level " + "\"%s\"", WHERE, name, policy_name(*site_level)); + INVALID_RETURN(tls->why, site_level); + break; + case TLS_LEV_FPRINT: + if (!tls->dane) + tls->dane = tls_dane_alloc(); + tls_dane_add_ee_digests(tls->dane, + var_smtp_tls_fpt_dgst, val, "|"); + break; + case TLS_LEV_VERIFY: + case TLS_LEV_SECURE: + if (tls->matchargv == 0) + tls->matchargv = argv_split(val, ":"); + else + argv_split_append(tls->matchargv, val, ":"); + break; + } + continue; + } + /* Only one instance per policy. */ + if (!strcasecmp(name, "exclude")) { + if (tls->exclusions) { + msg_warn("%s: attribute \"%s\" is specified multiple times", + WHERE, name); + INVALID_RETURN(tls->why, site_level); + } + tls->exclusions = vstring_strcpy(vstring_alloc(10), val); + continue; + } + /* Multiple instances per policy. */ + if (!strcasecmp(name, "tafile")) { + /* Only makes sense if we're using CA-based trust */ + if (!TLS_MUST_PKIX(*site_level)) { + msg_warn("%s: attribute \"%s\" invalid at security level" + " \"%s\"", WHERE, name, policy_name(*site_level)); + INVALID_RETURN(tls->why, site_level); + } + if (*val == 0) { + msg_warn("%s: attribute \"%s\" has empty value", WHERE, name); + INVALID_RETURN(tls->why, site_level); + } + if (!tls->dane) + tls->dane = tls_dane_alloc(); + if (!tls_dane_load_trustfile(tls->dane, val)) { + INVALID_RETURN(tls->why, site_level); + } + continue; + } + /* Last one wins. */ + if (!strcasecmp(name, "connection_reuse")) { + if (strcasecmp(val, "yes") == 0) { + tls->conn_reuse = 1; + } else if (strcasecmp(val, "no") == 0) { + tls->conn_reuse = 0; + } else { + msg_warn("%s: attribute \"%s\" has bad value: \"%s\"", + WHERE, name, val); + INVALID_RETURN(tls->why, site_level); + } + continue; + } + msg_warn("%s: invalid attribute name: \"%s\"", WHERE, name); + INVALID_RETURN(tls->why, site_level); + } + + FREE_RETURN; +} + +/* tls_policy_lookup - look up destination TLS policy */ + +static void tls_policy_lookup(SMTP_TLS_POLICY *tls, int *site_level, + const char *site_name, + const char *site_class) +{ + + /* + * Only one lookup with [nexthop]:port, [nexthop] or nexthop:port These + * are never the domain part of localpart@domain, rather they are + * explicit nexthops from transport:nexthop, and match only the + * corresponding policy. Parent domain matching (below) applies only to + * sub-domains of the recipient domain. + * + * XXX UNIX-domain connections query with the pathname as destination. + */ + if (!valid_utf8_hostname(var_smtputf8_enable, site_name, DONT_GRIPE)) { + tls_policy_lookup_one(tls, site_level, site_name, site_class); + return; + } + do { + tls_policy_lookup_one(tls, site_level, site_name, site_class); + } while (*site_level == TLS_LEV_NOTFOUND + && (site_name = strchr(site_name + 1, '.')) != 0); +} + +/* load_tas - load one or more ta files */ + +static int load_tas(TLS_DANE *dane, const char *files) +{ + int ret = 0; + char *save = mystrdup(files); + char *buf = save; + char *file; + + do { + if ((file = mystrtok(&buf, CHARS_COMMA_SP)) != 0) + ret = tls_dane_load_trustfile(dane, file); + } while (file && ret); + + myfree(save); + return (ret); +} + +/* set_cipher_grade - Set cipher grade and exclusions */ + +static void set_cipher_grade(SMTP_TLS_POLICY *tls) +{ + const char *mand_exclude = ""; + const char *also_exclude = ""; + + /* + * Use main.cf cipher level if no per-destination value specified. With + * mandatory encryption at least encrypt, and with mandatory verification + * at least authenticate! + */ + switch (tls->level) { + case TLS_LEV_INVALID: + case TLS_LEV_NONE: + return; + + case TLS_LEV_MAY: + if (tls->grade == 0) + tls->grade = mystrdup(var_smtp_tls_ciph); + break; + + case TLS_LEV_ENCRYPT: + if (tls->grade == 0) + tls->grade = mystrdup(var_smtp_tls_mand_ciph); + mand_exclude = var_smtp_tls_mand_excl; + also_exclude = "eNULL"; + break; + + case TLS_LEV_HALF_DANE: + case TLS_LEV_DANE: + case TLS_LEV_DANE_ONLY: + case TLS_LEV_FPRINT: + case TLS_LEV_VERIFY: + case TLS_LEV_SECURE: + if (tls->grade == 0) + tls->grade = mystrdup(var_smtp_tls_mand_ciph); + mand_exclude = var_smtp_tls_mand_excl; + also_exclude = "aNULL"; + break; + } + +#define ADD_EXCLUDE(vstr, str) \ + do { \ + if (*(str)) \ + vstring_sprintf_append((vstr), "%s%s", \ + VSTRING_LEN(vstr) ? " " : "", (str)); \ + } while (0) + + /* + * The "exclude" policy table attribute overrides main.cf exclusion + * lists. + */ + if (tls->exclusions == 0) { + tls->exclusions = vstring_alloc(10); + ADD_EXCLUDE(tls->exclusions, var_smtp_tls_excl_ciph); + ADD_EXCLUDE(tls->exclusions, mand_exclude); + } + ADD_EXCLUDE(tls->exclusions, also_exclude); +} + +/* policy_create - create SMTP TLS policy cache object (ctable call-back) */ + +static void *policy_create(const char *unused_key, void *context) +{ + SMTP_ITERATOR *iter = (SMTP_ITERATOR *) context; + int site_level; + const char *dest = STR(iter->dest); + const char *host = STR(iter->host); + + /* + * Prepare a pristine policy object. + */ + SMTP_TLS_POLICY *tls = (SMTP_TLS_POLICY *) mymalloc(sizeof(*tls)); + + smtp_tls_policy_init(tls, dsb_create()); + tls->conn_reuse = var_smtp_tls_conn_reuse; + + /* + * Compute the per-site TLS enforcement level. For compatibility with the + * original TLS patch, this algorithm is gives equal precedence to host + * and next-hop policies. + */ + tls->level = global_tls_level(); + site_level = TLS_LEV_NOTFOUND; + + if (tls_policy) { + tls_policy_lookup(tls, &site_level, dest, "next-hop destination"); + } else if (tls_per_site) { + tls_site_lookup(tls, &site_level, dest, "next-hop destination"); + if (site_level != TLS_LEV_INVALID + && strcasecmp_utf8(dest, host) != 0) + tls_site_lookup(tls, &site_level, host, "server hostname"); + + /* + * Override a wild-card per-site policy with a more specific global + * policy. + * + * With the original TLS patch, 1) a per-site ENCRYPT could not override + * a global VERIFY, and 2) a combined per-site (NONE+MAY) policy + * produced inconsistent results: it changed a global VERIFY into + * NONE, while producing MAY with all weaker global policy settings. + * + * With the current implementation, a combined per-site (NONE+MAY) + * consistently overrides global policy with NONE, and global policy + * can override only a per-site MAY wildcard. That is, specific + * policies consistently override wildcard policies, and + * (non-wildcard) per-site policies consistently override global + * policies. + */ + if (site_level == TLS_LEV_MAY && tls->level > TLS_LEV_MAY) + site_level = tls->level; + } + switch (site_level) { + default: + tls->level = site_level; + /* FALLTHROUGH */ + case TLS_LEV_NOTFOUND: + break; + case TLS_LEV_INVALID: + tls->level = site_level; + return ((void *) tls); + } + + /* + * DANE initialization may change the security level to something else, + * so do this early, so that we use the right level below. Note that + * "dane-only" changes to "dane" once we obtain the requisite TLSA + * records. + */ + if (TLS_DANE_BASED(tls->level)) + dane_init(tls, iter); + if (tls->level == TLS_LEV_INVALID) + return ((void *) tls); + + /* + * Use main.cf protocols and SNI settings if not set in per-destination + * table. + */ + if (tls->level > TLS_LEV_NONE && tls->protocols == 0) + tls->protocols = + mystrdup((tls->level == TLS_LEV_MAY) ? + var_smtp_tls_proto : var_smtp_tls_mand_proto); + if (tls->level > TLS_LEV_NONE && tls->sni == 0) { + if (!*var_smtp_tls_sni || valid_hostname(var_smtp_tls_sni, DONT_GRIPE)) + tls->sni = mystrdup(var_smtp_tls_sni); + else { + msg_warn("\"%s = %s\" specifies an invalid hostname", + VAR_LMTP_SMTP(TLS_SNI), var_smtp_tls_sni); + MARK_INVALID(tls->why, &tls->level); + return ((void *) tls); + } + } + + /* + * Compute cipher grade (if set in per-destination table, else + * set_cipher() uses main.cf settings) and security level dependent + * cipher exclusion list. + */ + set_cipher_grade(tls); + + /* + * Use main.cf cert_match setting if not set in per-destination table. + */ + switch (tls->level) { + case TLS_LEV_INVALID: + case TLS_LEV_NONE: + case TLS_LEV_MAY: + case TLS_LEV_ENCRYPT: + case TLS_LEV_HALF_DANE: + case TLS_LEV_DANE: + case TLS_LEV_DANE_ONLY: + break; + case TLS_LEV_FPRINT: + if (tls->dane == 0) + tls->dane = tls_dane_alloc(); + if (!TLS_DANE_HASEE(tls->dane)) { + tls_dane_add_ee_digests(tls->dane, var_smtp_tls_fpt_dgst, + var_smtp_tls_fpt_cmatch, CHARS_COMMA_SP); + if (!TLS_DANE_HASEE(tls->dane)) { + msg_warn("nexthop domain %s: configured at fingerprint " + "security level, but with no fingerprints to match.", + dest); + MARK_INVALID(tls->why, &tls->level); + return ((void *) tls); + } + } + break; + case TLS_LEV_VERIFY: + case TLS_LEV_SECURE: + if (tls->matchargv == 0) + tls->matchargv = + argv_split(tls->level == TLS_LEV_VERIFY ? + var_smtp_tls_vfy_cmatch : var_smtp_tls_sec_cmatch, + CHARS_COMMA_SP ":"); + if (*var_smtp_tls_tafile) { + if (tls->dane == 0) + tls->dane = tls_dane_alloc(); + if (!TLS_DANE_HASTA(tls->dane) + && !load_tas(tls->dane, var_smtp_tls_tafile)) { + MARK_INVALID(tls->why, &tls->level); + return ((void *) tls); + } + } + break; + default: + msg_panic("unexpected TLS security level: %d", tls->level); + } + + if (msg_verbose && tls->level != global_tls_level()) + msg_info("%s TLS level: %s", "effective", policy_name(tls->level)); + + return ((void *) tls); +} + +/* policy_delete - free no longer cached policy (ctable call-back) */ + +static void policy_delete(void *item, void *unused_context) +{ + SMTP_TLS_POLICY *tls = (SMTP_TLS_POLICY *) item; + + if (tls->protocols) + myfree(tls->protocols); + if (tls->sni) + myfree(tls->sni); + if (tls->grade) + myfree(tls->grade); + if (tls->exclusions) + vstring_free(tls->exclusions); + if (tls->matchargv) + argv_free(tls->matchargv); + if (tls->dane) + tls_dane_free(tls->dane); + dsb_free(tls->why); + + myfree((void *) tls); +} + +/* smtp_tls_policy_cache_query - cached lookup of TLS policy */ + +int smtp_tls_policy_cache_query(DSN_BUF *why, SMTP_TLS_POLICY *tls, + SMTP_ITERATOR *iter) +{ + VSTRING *key; + + /* + * Create an empty TLS Policy cache on the fly. + */ + if (policy_cache == 0) + policy_cache = + ctable_create(CACHE_SIZE, policy_create, policy_delete, (void *) 0); + + /* + * Query the TLS Policy cache, with a search key that reflects our shared + * values that also appear in other cache and table search keys. + */ + key = vstring_alloc(100); + smtp_key_prefix(key, ":", iter, SMTP_KEY_FLAG_CUR_NEXTHOP + | SMTP_KEY_FLAG_HOSTNAME + | SMTP_KEY_FLAG_PORT); + ctable_newcontext(policy_cache, (void *) iter); + *tls = *(SMTP_TLS_POLICY *) ctable_locate(policy_cache, STR(key)); + vstring_free(key); + + /* + * Report errors. Both error and non-error results are cached. We must + * therefore copy the cached DSN buffer content to the caller's buffer. + */ + if (tls->level == TLS_LEV_INVALID) { + /* XXX Simplify this by implementing a "copy" primitive. */ + dsb_update(why, + STR(tls->why->status), STR(tls->why->action), + STR(tls->why->mtype), STR(tls->why->mname), + STR(tls->why->dtype), STR(tls->why->dtext), + "%s", STR(tls->why->reason)); + return (0); + } else { + return (1); + } +} + +/* smtp_tls_policy_cache_flush - flush TLS policy cache */ + +void smtp_tls_policy_cache_flush(void) +{ + if (policy_cache != 0) { + ctable_free(policy_cache); + policy_cache = 0; + } +} + +/* global_tls_level - parse and cache var_smtp_tls_level */ + +static int global_tls_level(void) +{ + static int l = TLS_LEV_NOTFOUND; + + if (l != TLS_LEV_NOTFOUND) + return l; + + /* + * Compute the global TLS policy. This is the default policy level when + * no per-site policy exists. It also is used to override a wild-card + * per-site policy. + * + * We require that the global level is valid on startup. + */ + if (*var_smtp_tls_level) { + if ((l = tls_level_lookup(var_smtp_tls_level)) == TLS_LEV_INVALID) + msg_fatal("invalid tls security level: \"%s\"", var_smtp_tls_level); + } else if (var_smtp_enforce_tls) + l = var_smtp_tls_enforce_peername ? TLS_LEV_VERIFY : TLS_LEV_ENCRYPT; + else + l = var_smtp_use_tls ? TLS_LEV_MAY : TLS_LEV_NONE; + + if (msg_verbose) + msg_info("%s TLS level: %s", "global", policy_name(l)); + + return l; +} + +#define NONDANE_CONFIG 0 /* Administrator's fault */ +#define NONDANE_DEST 1 /* Remote server's fault */ +#define DANE_CANTAUTH 2 /* Remote server's fault */ + +static void PRINTFLIKE(4, 5) dane_incompat(SMTP_TLS_POLICY *tls, + SMTP_ITERATOR *iter, + int errtype, + const char *fmt,...) +{ + va_list ap; + + va_start(ap, fmt); + if (tls->level == TLS_LEV_DANE) { + tls->level = (errtype == DANE_CANTAUTH) ? TLS_LEV_ENCRYPT : TLS_LEV_MAY; + if (errtype == NONDANE_CONFIG) + vmsg_warn(fmt, ap); + else if (msg_verbose) + vmsg_info(fmt, ap); + } else { /* dane-only */ + if (errtype == NONDANE_CONFIG) { + vmsg_warn(fmt, ap); + MARK_INVALID(tls->why, &tls->level); + } else { + tls->level = TLS_LEV_INVALID; + vdsb_simple(tls->why, "4.7.5", fmt, ap); + } + } + va_end(ap); +} + +/* dane_init - special initialization for "dane" security level */ + +static void dane_init(SMTP_TLS_POLICY *tls, SMTP_ITERATOR *iter) +{ + TLS_DANE *dane; + + if (!iter->port) { + msg_warn("%s: the \"dane\" security level is invalid for delivery via" + " unix-domain sockets", STR(iter->dest)); + MARK_INVALID(tls->why, &tls->level); + return; + } + if (!tls_dane_avail()) { + dane_incompat(tls, iter, NONDANE_CONFIG, + "%s: %s configured, but no requisite library support", + STR(iter->dest), policy_name(tls->level)); + return; + } + if (!(smtp_host_lookup_mask & SMTP_HOST_FLAG_DNS) + || smtp_dns_support != SMTP_DNS_DNSSEC) { + dane_incompat(tls, iter, NONDANE_CONFIG, + "%s: %s configured with dnssec lookups disabled", + STR(iter->dest), policy_name(tls->level)); + return; + } + + /* + * If we ignore MX lookup errors, we also ignore DNSSEC security problems + * and thus avoid any reasonable expectation that we get the right DANE + * key material. + */ + if (smtp_mode && var_ign_mx_lookup_err) { + dane_incompat(tls, iter, NONDANE_CONFIG, + "%s: %s configured with MX lookup errors ignored", + STR(iter->dest), policy_name(tls->level)); + return; + } + + /* + * This is not optional, code in tls_dane.c assumes that the nexthop + * qname is already an fqdn. If we're using these flags to go from qname + * to rname, the assumption is invalid. Likewise we cannot add the qname + * to certificate name checks, ... + */ + if (smtp_dns_res_opt & (RES_DEFNAMES | RES_DNSRCH)) { + dane_incompat(tls, iter, NONDANE_CONFIG, + "%s: dns resolver options incompatible with %s TLS", + STR(iter->dest), policy_name(tls->level)); + return; + } + + /* + * When the MX name is present and insecure, DANE may not apply, we then + * either fail if DANE is mandatory or use regular opportunistic TLS if + * the insecure MX level is "may". + */ + if (iter->mx && !iter->mx->dnssec_valid + && (tls->level == TLS_LEV_DANE_ONLY || + smtp_tls_insecure_mx_policy <= TLS_LEV_MAY)) { + dane_incompat(tls, iter, NONDANE_DEST, "non DNSSEC destination"); + return; + } + /* When TLSA lookups fail, we defer the message */ + if ((dane = tls_dane_resolve(iter->port, "tcp", iter->rr, + var_smtp_tls_force_tlsa)) == 0) { + tls->level = TLS_LEV_INVALID; + dsb_simple(tls->why, "4.7.5", "TLSA lookup error for %s:%u", + STR(iter->host), ntohs(iter->port)); + return; + } + if (tls_dane_notfound(dane)) { + dane_incompat(tls, iter, NONDANE_DEST, "no TLSA records found"); + tls_dane_free(dane); + return; + } + + /* + * Some TLSA records found, but none usable, per + * + * https://tools.ietf.org/html/draft-ietf-dane-srv-02#section-4 + * + * we MUST use TLS, and SHALL use full PKIX certificate checks. The latter + * would be unwise for SMTP: no human present to "click ok" and risk of + * non-delivery in most cases exceeds risk of interception. + * + * We also have a form of Goedel's incompleteness theorem in play: any list + * of public root CA certs is either incomplete or inconsistent (for any + * given verifier some of the CAs are surely not trustworthy). + */ + if (tls_dane_unusable(dane)) { + dane_incompat(tls, iter, DANE_CANTAUTH, "TLSA records unusable"); + tls_dane_free(dane); + return; + } + + /* + * Perhaps downgrade to "encrypt" if MX is insecure. + */ + if (iter->mx && !iter->mx->dnssec_valid) { + if (smtp_tls_insecure_mx_policy == TLS_LEV_ENCRYPT) { + dane_incompat(tls, iter, DANE_CANTAUTH, + "Verification not possible, MX RRset is insecure"); + tls_dane_free(dane); + return; + } + if (tls->level != TLS_LEV_DANE + || smtp_tls_insecure_mx_policy != TLS_LEV_DANE) + msg_panic("wrong state for insecure MX host DANE policy"); + + /* For correct logging in tls_client_start() */ + tls->level = TLS_LEV_HALF_DANE; + } + + /* + * With DANE trust anchors, peername matching is not configurable. + */ + if (TLS_DANE_HASTA(dane)) { + tls->matchargv = argv_alloc(2); + argv_add(tls->matchargv, dane->base_domain, ARGV_END); + if (iter->mx) { + if (strcmp(iter->mx->qname, iter->mx->rname) == 0) + argv_add(tls->matchargv, iter->mx->qname, ARGV_END); + else + argv_add(tls->matchargv, iter->mx->rname, + iter->mx->qname, ARGV_END); + } + } else if (!TLS_DANE_HASEE(dane)) + msg_panic("empty DANE match list"); + tls->dane = dane; + return; +} + +#endif |