From e0e6c0c59639cfed7b63b896b32a55fb2c50b11c Mon Sep 17 00:00:00 2001 From: Wietse Venema Date: Fri, 7 Aug 2009 00:00:00 -0500 Subject: [PATCH] postfix-2.6.4-RC2 --- postfix/HISTORY | 38 ++++++++--- postfix/RELEASE_NOTES | 25 ++++--- postfix/src/global/mail_version.h | 4 +- postfix/src/smtpd/smtpd_check.c | 104 ++++++++++++++++++++++-------- 4 files changed, 123 insertions(+), 48 deletions(-) diff --git a/postfix/HISTORY b/postfix/HISTORY index 7067bd124..a01fca1c5 100644 --- a/postfix/HISTORY +++ b/postfix/HISTORY @@ -15270,13 +15270,33 @@ Apologies for any names omitted. feature can be used meaningfully at any protocol stage. File: proto/postconf.proto. -20090803 +20090805 - Workaround: with some local DNS servers including BIND, it - is possible that A or MX lookups succeed, while NS lookups - for the same domains time out. Spammers use this to avoid - access restrictions. To deal with future variations of - this, check_{client,helo,sender,etc}_{mx,ns,etc}_access no - longer tolerate any lookup failures. Instead, they reply - with $access_map_defer_code or $access_map_reject_code as - appropriate. File: smtpd/smtpd_check.c. + Bugfix: don't panic when an unexpected smtpd access map is + specified. File: smtpd/smtpd_check.c. + +20090807 + + Workaround: NS record lookups for certain domains always + fail, while other queries for those domains always succeed + (and even return replies with NS records as additional + information). + + This inconsistency would allow spammers to avoid the Postfix + check_{client,helo,sender,etc}_ns_access restrictions, + because those restrictions have effect only for names that + are known in the DNS. + + To address this specific inconsistency, the Postfix + check_{client,etc}_ns_access feature now requires that a + known-in-DNS domain name (or parent thereof) resolves to + at least one name server IP address. + + For consistency, check_{client,etc}_mx_access now requires + that a known-in-DNS domain name resolves to at least one + mail server IP address. + + The IP addresses thus obtained may or may not be "correct". + There is little to stop an uncooperative DNS server from + lying, especially when the owner of the domain has no + intention to receive email. File: smtpd/smtpd_check.c. diff --git a/postfix/RELEASE_NOTES b/postfix/RELEASE_NOTES index 8c720bbef..f17d914c9 100644 --- a/postfix/RELEASE_NOTES +++ b/postfix/RELEASE_NOTES @@ -17,18 +17,23 @@ before proceeding. Incompatibility with Postfix 2.6.4 ================================== -The check_{client,helo,sender,etc}_{mx,ns,etc}_access features no -longer tolerate any lookup failures. Instead, they now reply with -$access_map_defer_code or $access_map_reject_code as appropriate. +With some domain names, NS record lookups always fail while other +lookups always succeed (and may even return NS records as additional +information). This anomaly could be used by evil elements to skip +Postfix check_{client,helo,sender,recipient}_ns_access checks, +because these apply only to domains that are known in the DNS. -The reason for this change is that spammers are using tricks where -A or MX lookups succeed while NS lookups for the same domains fail, -depending local DNS infrastructure details. The change deals with -future variants of this anomalous behavior. +To address this specific problem, check_{client,etc}_ns_access now +requires that a known-in-DNS domain name (or parent thereof) resolves +to at least one name server IP address. -As a side effect, non-existent domain names in HELO commands will -now trigger a REJECT action with check_helo_{mx,ns}_access, where -previously such commands were silently permitted. +For consistency, check_{client,etc}_mx_access now requires that a +known-in-DNS domain name resolves to at least one mail server IP +address. + +Keep in mind that these measures provide no hard assurances. There +is little to stop an uncooperative DNS server from lying, especially +when the owner of the domain has no intention to receive email. Major changes - multi-instance support -------------------------------------- diff --git a/postfix/src/global/mail_version.h b/postfix/src/global/mail_version.h index dce91ae4b..52f91ed27 100644 --- a/postfix/src/global/mail_version.h +++ b/postfix/src/global/mail_version.h @@ -20,8 +20,8 @@ * Patches change both the patchlevel and the release date. Snapshots have no * patchlevel; they change the release date only. */ -#define MAIL_RELEASE_DATE "20090803" -#define MAIL_VERSION_NUMBER "2.6.4-RC1" +#define MAIL_RELEASE_DATE "20090807" +#define MAIL_VERSION_NUMBER "2.6.4-RC2" #ifdef SNAPSHOT # define MAIL_VERSION_DATE "-" MAIL_RELEASE_DATE diff --git a/postfix/src/smtpd/smtpd_check.c b/postfix/src/smtpd/smtpd_check.c index 74d86ec47..a2e04f4cb 100644 --- a/postfix/src/smtpd/smtpd_check.c +++ b/postfix/src/smtpd/smtpd_check.c @@ -2315,8 +2315,13 @@ static int check_access(SMTPD_STATE *state, const char *table, const char *name, if (msg_verbose) msg_info("%s: %s", myname, name); - if ((dict = dict_handle(table)) == 0) - msg_panic("%s: dictionary not found: %s", myname, table); + if ((dict = dict_handle(table)) == 0) { + msg_warn("%s: unexpected dictionary: %s", myname, table); + value = "451 4.3.5 Server configuration error"; + CHK_ACCESS_RETURN(check_table_result(state, table, value, name, + reply_name, reply_class, + def_acl), FOUND); + } if (flags == 0 || (flags & dict->flags) != 0) { if ((value = dict_get(dict, name)) != 0) CHK_ACCESS_RETURN(check_table_result(state, table, value, name, @@ -2360,8 +2365,13 @@ static int check_domain_access(SMTPD_STATE *state, const char *table, */ #define CHK_DOMAIN_RETURN(x,y) { *found = y; return(x); } - if ((dict = dict_handle(table)) == 0) - msg_panic("%s: dictionary not found: %s", myname, table); + if ((dict = dict_handle(table)) == 0) { + msg_warn("%s: unexpected dictionary: %s", myname, table); + value = "451 4.3.5 Server configuration error"; + CHK_DOMAIN_RETURN(check_table_result(state, table, value, + domain, reply_name, reply_class, + def_acl), FOUND); + } for (name = domain; *name != 0; name = next) { if (flags == 0 || (flags & dict->flags) != 0) { if ((value = dict_get(dict, name)) != 0) @@ -2419,8 +2429,13 @@ static int check_addr_access(SMTPD_STATE *state, const char *table, #endif delim = '.'; - if ((dict = dict_handle(table)) == 0) - msg_panic("%s: dictionary not found: %s", myname, table); + if ((dict = dict_handle(table)) == 0) { + msg_warn("%s: unexpected dictionary: %s", myname, table); + value = "451 4.3.5 Server configuration error"; + CHK_ADDR_RETURN(check_table_result(state, table, value, address, + reply_name, reply_class, + def_acl), FOUND); + } do { if (flags == 0 || (flags & dict->flags) != 0) { if ((value = dict_get(dict, addr)) != 0) @@ -2500,6 +2515,10 @@ static int check_server_access(SMTPD_STATE *state, const char *table, struct addrinfo *res; int status; INET_PROTO_INFO *proto_info; + const char *saved_domain; + int non_err, soft_err; + int known_name_in_dns; + int ping_status; /* * Sanity check. @@ -2554,15 +2573,26 @@ static int check_server_access(SMTPD_STATE *state, const char *table, * * If the domain name exists but no NS record exists, look up parent domain * NS records. + * + * After the initial lookup fails, do one final DNS sanity check. Reject + * mail when the name exists, but MX lookup produces no valid response or + * NS lookup fails for any reason. Beware, this sanity check provides no + * hard assurance. An uncooperative DNS server may lie about everything, + * including non-existence. */ +#define SOME_DNS_RR_EXISTS(stat, herr) \ + ((stat) == DNS_OK || (stat) == DNS_INVAL || (herr) == NO_DATA) + + saved_domain = domain; dns_status = dns_lookup(domain, type, 0, &server_list, (VSTRING *) 0, (VSTRING *) 0); - if (dns_status == DNS_NOTFOUND && h_errno == NO_DATA) { + known_name_in_dns = SOME_DNS_RR_EXISTS(dns_status, h_errno); + if (dns_status == DNS_NOTFOUND /* Not: h_errno == NO_DATA */ ) { if (type == T_MX) { server_list = dns_rr_create(domain, domain, type, C_IN, 0, 0, domain, strlen(domain) + 1); dns_status = DNS_OK; - } else if (type == T_NS) { + } else if (type == T_NS && h_errno == NO_DATA) { while ((domain = strchr(domain, '.')) != 0 && domain[1]) { domain += 1; dns_status = dns_lookup(domain, type, 0, &server_list, @@ -2575,14 +2605,23 @@ static int check_server_access(SMTPD_STATE *state, const char *table, if (dns_status != DNS_OK) { msg_warn("Unable to look up %s host for %s: %s", dns_strtype(type), domain && domain[1] ? domain : name, dns_strerror(h_errno)); - /* No mercy for DNS failure. */ - return (smtpd_check_reject(state, MAIL_ERROR_POLICY, - dns_status == DNS_NOTFOUND ? - var_map_reject_code : var_map_defer_code, - smtpd_dsn_fix("4.1.8", reply_class), - "<%s>: %s rejected: %s", - reply_name, reply_class, - "Domain not found")); + if (known_name_in_dns == 0) { + /* With hostile DNS, an address query is more likely to work. */ + ping_status = dns_lookup_l(saved_domain, 0, (DNS_RR **) 0, + (VSTRING *) 0, (VSTRING *) 0, + DNS_REQ_FLAG_STOP_OK, + RR_ADDR_TYPES, 0); + known_name_in_dns = SOME_DNS_RR_EXISTS(ping_status, h_errno); + } + if (known_name_in_dns) + return (smtpd_check_reject(state, MAIL_ERROR_POLICY, + dns_status == DNS_RETRY ? + var_map_defer_code : var_map_reject_code, + smtpd_dsn_fix("4.1.8", reply_class), + "<%s>: %s rejected: %s", + reply_name, reply_class, + "Domain not found")); + return (SMTPD_CHECK_DUNNO); } /* @@ -2594,10 +2633,19 @@ static int check_server_access(SMTPD_STATE *state, const char *table, * Check the hostnames first, then the addresses. */ proto_info = inet_proto_info(); + non_err = soft_err = 0; for (server = server_list; server != 0; server = server->next) { if (msg_verbose) msg_info("%s: %s hostname check: %s", myname, dns_strtype(type), (char *) server->data); + if (valid_hostaddr((char *) server->data, DONT_GRIPE)) { + non_err = 1; + if ((status = check_addr_access(state, table, (char *) server->data, + FULL, &found, reply_name, reply_class, + def_acl)) != 0 || found) + CHECK_SERVER_RETURN(status); + continue; + } if ((status = check_domain_access(state, table, (char *) server->data, FULL, &found, reply_name, reply_class, def_acl)) != 0 || found) @@ -2607,17 +2655,11 @@ static int check_server_access(SMTPD_STATE *state, const char *table, msg_warn("Unable to look up %s host %s for %s %s: %s", dns_strtype(type), (char *) server->data, reply_class, reply_name, MAI_STRERROR(aierr)); - /* No mercy for DNS failure. */ - status = smtpd_check_reject(state, - MAIL_ERROR_POLICY, - aierr == EAI_NONAME ? - var_map_reject_code : var_map_defer_code, - smtpd_dsn_fix("4.1.8", reply_class), - "<%s>: %s rejected: %s", - reply_name, reply_class, - "Domain not found"); - CHECK_SERVER_RETURN(status); + if (aierr == EAI_AGAIN || aierr == EAI_SYSTEM) + soft_err = 1; + continue; } + non_err = 1; /* Now we must also free the addrinfo result. */ if (msg_verbose) msg_info("%s: %s host address check: %s", @@ -2641,7 +2683,15 @@ static int check_server_access(SMTPD_STATE *state, const char *table, } freeaddrinfo(res0); /* 200412 */ } - CHECK_SERVER_RETURN(SMTPD_CHECK_DUNNO); + status = non_err ? SMTPD_CHECK_DUNNO : + smtpd_check_reject(state, MAIL_ERROR_POLICY, + soft_err ? var_map_defer_code : + var_map_reject_code, + smtpd_dsn_fix("4.1.8", reply_class), + "<%s>: %s rejected: %s", + reply_name, reply_class, + "Domain not found"); + CHECK_SERVER_RETURN(status); } /* check_ccert_access - access for TLS clients by certificate fingerprint */