X-Git-Url: https://git.exim.org/users/jgh/exim.git/blobdiff_plain/0f06b4f296802e4e13188c740ea09419931a3020..cdeb6856e69a0035df8fc06f11787c755a1cc274:/doc/doc-txt/experimental-spec.txt diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt index 2f44fce26..16c0f56da 100644 --- a/doc/doc-txt/experimental-spec.txt +++ b/doc/doc-txt/experimental-spec.txt @@ -759,11 +759,12 @@ b. Configure, somewhere before the DATA ACL, the control option to -Transport post-delivery actions +Event Actions -------------------------------------------------------------- -An arbitrary per-transport string can be expanded upon various transport events -and (for SMTP transports) a second string on deferrals caused by a host error. +(Renamed from TPDA, Transport post-delivery actions) + +An arbitrary per-transport string can be expanded upon various transport events. Additionally a main-section configuration option can be expanded on some per-message events. This feature may be used, for example, to write exim internal log information @@ -771,33 +772,33 @@ This feature may be used, for example, to write exim internal log information In order to use the feature, you must compile with -EXPERIMENTAL_TPDA=yes +EXPERIMENTAL_EVENT=yes in your Local/Makefile and define one or both of -- the tpda_event_action option in the transport -- the delivery_event_action +- the event_action option in the transport +- the event_action main option to be expanded when the event fires. -A new variable, $tpda_event, is set to the event type when the +A new variable, $event_name, is set to the event type when the expansion is done. The current list of events is: - msg:complete main per message - msg:delivery transport per recipient - msg:host:defer transport per attempt - msg:fail:delivery main per recipient - msg:fail:internal main per recipient - tcp:connect transport per connection - tcp:close transport per connection - tls:cert transport per certificate in verification chain - smtp:connect transport per connection - -The expansion is called for all event types, and should use the $tpda_event + msg:complete after main per message + msg:delivery after transport per recipient + msg:host:defer after transport per attempt + msg:fail:delivery after main per recipient + msg:fail:internal after main per recipient + tcp:connect before transport per connection + tcp:close after transport per connection + tls:cert before both per certificate in verification chain + smtp:connect after transport per connection + +The expansion is called for all event types, and should use the $event_name value to decide when to act. The variable data is a colon-separated list, describing an event tree. -There is an auxilary variable, $tpda_data, for which the +There is an auxilary variable, $event_data, for which the content is event_dependent: msg:delivery smtp confirmation mssage @@ -805,7 +806,7 @@ content is event_dependent: tls:cert verification chain depth smtp:connect smtp banner -The msg:host:defer event populates one extra variable, $tpda_defer_errno. +The msg:host:defer event populates one extra variable, $event_defer_errno. The following variables are likely to be useful depending on the event type: @@ -815,12 +816,12 @@ The following variables are likely to be useful depending on the event type: tls_out_peercert lookup_dnssec_authenticated, tls_out_dane sending_ip_address, sending_port - message_exim_id + message_exim_id, verify_mode An example might look like: -tpda_event_action = ${if = {msg:delivery}{$tpda_event} \ +event_action = ${if = {msg:delivery}{$event_name} \ {${lookup pgsql {SELECT * FROM record_Delivery( \ '${quote_pgsql:$sender_address_domain}',\ '${quote_pgsql:${lc:$sender_address_local_part}}', \ @@ -831,12 +832,12 @@ tpda_event_action = ${if = {msg:delivery}{$tpda_event} \ '${quote_pgsql:$message_exim_id}')}} \ } {}} -The string is expanded for each of the supported events and any -side-effects will happen. The result is then discarded. +The string is expanded when each of the supported events occur +and any side-effects of the expansion will happen. Note that for complex operations an ACL expansion can be used. -The expansion of the tpda_event_action option should normally +The expansion of the event_action option should normally return an empty string. Should it return anything else the following will be forced: @@ -848,8 +849,13 @@ following will be forced: tls:cert refuse verification smtp:connect close connection +No other use is made of the result string. +Known issues: +- the tls:cert event is only called for the cert chain elements + received over the wire, with GnuTLS. OpenSSL gives the entire + chain including thse loaded locally. Redis Lookup @@ -1138,22 +1144,6 @@ the next hop does not support DSN. Adding it to a redirect router makes no difference. -Certificate name checking --------------------------------------------------------------- -The X509 certificates used for TLS are supposed be verified -that they are owned by the expected host. The coding of TLS -support to date has not made these checks. - -If built with EXPERIMENTAL_CERTNAMES defined, code is -included to do so, and a new smtp transport option -"tls_verify_cert_hostname" supported which takes a list of -names for which the checks must be made. The host must -also be in "tls_verify_hosts". - -Both Subject and Subject-Alternate-Name certificate fields -are supported, as are wildcard certificates (limited to -a single wildcard being the initial component of a 3-or-more -component FQDN). DANE @@ -1178,6 +1168,10 @@ admins of the target server. The attack surface presented by (a) is thought to be smaller than that of the set of root CAs. +It also allows the server to declare (implicitly) that +connections to it should use TLS. An MITM could simply +fail to pass on a server's STARTTLS. + DANE scales better than having to maintain (and side-channel communicate) copies of server certificates for every possible target server. It also scales @@ -1202,12 +1196,12 @@ There are no changes to Exim specific to server-side operation of DANE. The TLSA record for the server may have "certificate -usage" of DANE_TA(2) or DANE_EE(3). The latter specifies +usage" of DANE-TA(2) or DANE-EE(3). The latter specifies the End Entity directly, i.e. the certificate involved is that of the server (and should be the sole one transmitted during the TLS handshake); this is appropriate for a single system, using a self-signed certificate. - DANE_TA usage is effectively declaring a specific CA + DANE-TA usage is effectively declaring a specific CA to be used; this might be a private CA or a public, well-known one. A private CA at simplest is just a self-signed certificate which is used to sign @@ -1219,7 +1213,7 @@ the entire certificate chain from CA to server-certificate. If a public CA is used then all clients must be primed with it (losing one advantage of DANE) - but the attack surface is reduced from all public CAs to that single CA. -DANE_TA is commonly used for several services and/or +DANE-TA is commonly used for several services and/or servers, each having a TLSA query-domain CNAME record, all of which point to a single TLSA record. @@ -1236,13 +1230,13 @@ is useful for quickly generating TLSA records; and commands like are workable for 4th-field hashes. -For use with the DANE_TA model, server certificates +For use with the DANE-TA model, server certificates must have a correct name (SubjectName or SubjectAltName). The use of OCSP-stapling should be considered, allowing for fast revocation of certificates (which would otherwise be limited by the DNS TTL on the TLSA records). However, -this is likely to only be usable with DANE_TA. NOTE: the +this is likely to only be usable with DANE-TA. NOTE: the default of requesting OCSP for all hosts is modified iff DANE is in use, to: @@ -1253,10 +1247,10 @@ DANE is in use, to: The (new) variable $tls_out_tlsa_usage is a bitfield with numbered bits set for TLSA record usage codes. The zero above means DANE was not in use, -the four means that only DANE_TA usage TLSA records were -found. If the definition of hosts_require_ocsp or -hosts_request_ocsp includes the string "tls_out_tlsa_usage", -they are re-expanded in time to control the OCSP request. +the four means that only DANE-TA usage TLSA records were +found. If the definition of hosts_request_ocsp includes the +string "tls_out_tlsa_usage", they are re-expanded in time to +control the OCSP request. This modification of hosts_request_ocsp is only done if it has the default value of "*". Admins who change it, and @@ -1271,9 +1265,15 @@ hosts_try_dane and hosts_require_dane. They do the obvious thing. DANE will only be usable if the target host has DNSSEC-secured MX, A and TLSA records. +A TLSA lookup will be done if either of the above options match +and the host-lookup succeded using dnssec. +If the TLSA lookup succeeds, a TLS connection will be required +for the host. + (TODO: specify when fallback happens vs. when the host is not used) If dane is in use the following transport options are ignored: + hosts_require_tls tls_verify_hosts tls_try_verify_hosts tls_verify_certificates @@ -1288,7 +1288,7 @@ in the delivery log line will show as "CV=dane". There is a new variable $tls_out_dane which will have "yes" if verification succeeded using DANE and "no" otherwise (only useful -in combination with EXPERIMENTAL_TPDA), and a new variable +in combination with EXPERIMENTAL_EVENT), and a new variable $tls_out_tlsa_usage (detailed above).