Expansions: A tls option on ${readsocket }. Bug 2282

[users/jgh/exim.git] / doc / doc-docbook / spec.xfpt

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index b1cc46862743cda0f8fc56ebf931a7655d6b5ad2..8b939b52b1e66d5d20a47c97e2df805a7e48610a 100644 (file)
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -9434,11 +9434,14 @@ letters appear. For example:
         &*$h_*&<&'header&~name'&>&*:*&" &&&
        "&*$bheader_*&<&'header&~name'&>&*:*&&~or&~&&&
         &*$bh_*&<&'header&~name'&>&*:*&" &&&
         &*$h_*&<&'header&~name'&>&*:*&" &&&
        "&*$bheader_*&<&'header&~name'&>&*:*&&~or&~&&&
         &*$bh_*&<&'header&~name'&>&*:*&" &&&

+       "&*$lheader_*&<&'header&~name'&>&*:*&&~or&~&&&
+        &*$lh_*&<&'header&~name'&>&*:*&"

        "&*$rheader_*&<&'header&~name'&>&*:*&&~or&~&&&
         &*$rh_*&<&'header&~name'&>&*:*&"
 .cindex "expansion" "header insertion"
 .vindex "&$header_$&"
 .vindex "&$bheader_$&"
        "&*$rheader_*&<&'header&~name'&>&*:*&&~or&~&&&
         &*$rh_*&<&'header&~name'&>&*:*&"
 .cindex "expansion" "header insertion"
 .vindex "&$header_$&"
 .vindex "&$bheader_$&"

+.vindex "&$lheader_$&"

 .vindex "&$rheader_$&"
 .cindex "header lines" "in expansion strings"
 .cindex "header lines" "character sets"
 .vindex "&$rheader_$&"
 .cindex "header lines" "in expansion strings"
 .cindex "header lines" "character sets"


@@ -9451,7 +9454,7 @@ The newline that terminates a header line is not included in the expansion, but
 internal newlines (caused by splitting the header line over several physical
 lines) may be present.
 
 internal newlines (caused by splitting the header line over several physical
 lines) may be present.
 

-The difference between &%rheader%&, &%bheader%&, and &%header%& is in the way
+The difference between the four pairs of expansions is in the way

 the data in the header line is interpreted.
 
 .ilist
 the data in the header line is interpreted.
 
 .ilist


@@ -9459,6 +9462,15 @@ the data in the header line is interpreted.
 &%rheader%& gives the original &"raw"& content of the header line, with no
 processing at all, and without the removal of leading and trailing white space.
 
 &%rheader%& gives the original &"raw"& content of the header line, with no
 processing at all, and without the removal of leading and trailing white space.
 

+.next
+.cindex "list" "of header lines"
+&%lheader%& gives a colon-separated list, one element per header when there
+are multiple headers with a given name.
+Any embedded colon characters within an element are doubled, so normal Exim
+list-processing facilities can be used.
+The terminating newline of each element is removed; in other respects
+the content is &"raw"&.
+

 .next
 .cindex "base64 encoding" "in header lines"
 &%bheader%& removes leading and trailing white space, and then decodes base64
 .next
 .cindex "base64 encoding" "in header lines"
 &%bheader%& removes leading and trailing white space, and then decodes base64


@@ -9866,15 +9878,26 @@ extend what can be done. Firstly, you can vary the timeout. For example:
 .code
 ${readsocket{/socket/name}{request string}{3s}}
 .endd
 .code
 ${readsocket{/socket/name}{request string}{3s}}
 .endd

+

 The third argument is a list of options, of which the first element is the timeout
 and must be present if the argument is given.
 Further elements are options of form &'name=value'&.
 The third argument is a list of options, of which the first element is the timeout
 and must be present if the argument is given.
 Further elements are options of form &'name=value'&.

-One option type is currently recognised, defining whether (the default)
+Two option types is currently recognised: shutdown and tls.
+The first defines whether (the default)

 or not a shutdown is done on the connection after sending the request.
 Example, to not do so (preferred, eg. by some webservers):
 .code
 ${readsocket{/socket/name}{request string}{3s:shutdown=no}}
 .endd
 or not a shutdown is done on the connection after sending the request.
 Example, to not do so (preferred, eg. by some webservers):
 .code
 ${readsocket{/socket/name}{request string}{3s:shutdown=no}}
 .endd

+.new
+The second, tls, controls the use of TLS on the connection.  Example:
+.code
+${readsocket{/socket/name}{request string}{3s:tls=yes}}
+.endd
+The default is to not use TLS.
+If it is enabled, a shutdown as descripbed above is never done.
+.wen
+

 A fourth argument allows you to change any newlines that are in the data
 that is read, in the same way as for &%readfile%& (see above). This example
 turns them into spaces:
 A fourth argument allows you to change any newlines that are in the data
 that is read, in the same way as for &%readfile%& (see above). This example
 turns them into spaces:


@@ -13861,6 +13884,7 @@ listed in more than one group.
 .row &%av_scanner%&                  "specify virus scanner"
 .row &%check_rfc2047_length%&        "check length of RFC 2047 &""encoded &&&
                                       words""&"
 .row &%av_scanner%&                  "specify virus scanner"
 .row &%check_rfc2047_length%&        "check length of RFC 2047 &""encoded &&&
                                       words""&"

+.row &%dns_cname_loops%&             "follow CNAMEs returned by resolver"

 .row &%dns_csa_search_limit%&        "control CSA parent search depth"
 .row &%dns_csa_use_reverse%&         "en/disable CSA IP reverse search"
 .row &%header_maxsize%&              "total size of message header"
 .row &%dns_csa_search_limit%&        "control CSA parent search depth"
 .row &%dns_csa_use_reverse%&         "en/disable CSA IP reverse search"
 .row &%header_maxsize%&              "total size of message header"


@@ -14763,6 +14787,19 @@ This option controls whether or not an IP address, given as a CSA domain, is
 reversed and looked up in the reverse DNS, as described in more detail in
 section &<<SECTverifyCSA>>&.
 
 reversed and looked up in the reverse DNS, as described in more detail in
 section &<<SECTverifyCSA>>&.
 

+.new
+.option dns_cname_loops main integer 1
+.cindex DNS "CNAME following"
+This option controls the following of CNAME chains, needed if the resolver does
+not do it internally.
+As of 2018 most should, and the default can be left.
+If you have an ancient one, a value of 10 is likely needed.
+
+The default value of one CNAME-follow is needed
+thanks to the observed return for an MX request,
+given no MX presence but a CNAME to an A, of the CNAME.
+.wen
+

 
 .option dns_dnssec_ok main integer -1
 .cindex "DNS" "resolver options"
 
 .option dns_dnssec_ok main integer -1
 .cindex "DNS" "resolver options"


@@ -15082,7 +15119,7 @@ server. This reduces security slightly, but improves interworking with older
 implementations of TLS.
 
 
 implementations of TLS.
 
 

-option gnutls_allow_auto_pkcs11 main boolean unset
+.option gnutls_allow_auto_pkcs11 main boolean unset

 This option will let GnuTLS (2.12.0 or later) autoload PKCS11 modules with
 the p11-kit configuration files in &_/etc/pkcs11/modules/_&.
 
 This option will let GnuTLS (2.12.0 or later) autoload PKCS11 modules with
 the p11-kit configuration files in &_/etc/pkcs11/modules/_&.
 


@@ -17369,7 +17406,7 @@ The ordering of the two lists must match.
 .cindex SSMTP
 .cindex SMTPS
 This option specifies a list of incoming SSMTP (aka SMTPS) ports that should
 .cindex SSMTP
 .cindex SMTPS
 This option specifies a list of incoming SSMTP (aka SMTPS) ports that should

-operate the obsolete SSMTP (SMTPS) protocol, where a TLS session is immediately
+operate the SSMTP (SMTPS) protocol, where a TLS session is immediately

 set up without waiting for the client to issue a STARTTLS command. For
 further details, see section &<<SECTsupobssmt>>&.
 
 set up without waiting for the client to issue a STARTTLS command. For
 further details, see section &<<SECTsupobssmt>>&.
 


@@ -23950,14 +23987,15 @@ the message. As a result, the overall timeout for a message depends on the size
 of the message. Its value must not be zero. See also &%final_timeout%&.
 
 
 of the message. Its value must not be zero. See also &%final_timeout%&.
 
 

+.option dkim_canon smtp string&!! unset

 .option dkim_domain smtp string list&!! unset
 .option dkim_domain smtp string list&!! unset

-.option dkim_selector smtp string&!! unset
+.option dkim_hash smtp string&!! sha256
+.option dkim_identity smtp string&!! unset

 .option dkim_private_key smtp string&!! unset
 .option dkim_private_key smtp string&!! unset

-.option dkim_canon smtp string&!! unset
+.option dkim_selector smtp string&!! unset

 .option dkim_strict smtp string&!! unset
 .option dkim_sign_headers smtp string&!! "per RFC"
 .option dkim_strict smtp string&!! unset
 .option dkim_sign_headers smtp string&!! "per RFC"

-.option dkim_hash smtp string&!! sha256
-.option dkim_identity smtp string&!! unset
+.option dkim_timestamps smtp string&!! unset

 DKIM signing options.  For details see section &<<SECDKIMSIGN>>&.
 
 
 DKIM signing options.  For details see section &<<SECDKIMSIGN>>&.
 
 


@@ -26742,7 +26780,7 @@ authenticator only. There is only one option:
 
 .option server_socket dovecot string unset
 
 
 .option server_socket dovecot string unset
 

-This option must specify the socket that is the interface to Dovecot
+This option must specify the UNIX socket that is the interface to Dovecot

 authentication. The &%public_name%& option must specify an authentication
 mechanism that Dovecot is configured to support. You can have several
 authenticators for different mechanisms. For example:
 authentication. The &%public_name%& option must specify an authentication
 mechanism that Dovecot is configured to support. You can have several
 authenticators for different mechanisms. For example:


@@ -27390,7 +27428,10 @@ the size of the generated prime, so it might still be too large.
 .oindex "&%tls_require_ciphers%&" "OpenSSL"
 There is a function in the OpenSSL library that can be passed a list of cipher
 suites before the cipher negotiation takes place. This specifies which ciphers
 .oindex "&%tls_require_ciphers%&" "OpenSSL"
 There is a function in the OpenSSL library that can be passed a list of cipher
 suites before the cipher negotiation takes place. This specifies which ciphers

-are acceptable. The list is colon separated and may contain names like
+.new
+are acceptable for TLS versions prior to 1.3.
+.wen
+The list is colon separated and may contain names like

 DES-CBC3-SHA. Exim passes the expanded value of &%tls_require_ciphers%&
 directly to this function call.
 Many systems will install the OpenSSL manual-pages, so you may have
 DES-CBC3-SHA. Exim passes the expanded value of &%tls_require_ciphers%&
 directly to this function call.
 Many systems will install the OpenSSL manual-pages, so you may have


@@ -27455,6 +27496,18 @@ This example will prefer ECDSA-authenticated ciphers over RSA ones:
 tls_require_ciphers = ECDSA:RSA:!COMPLEMENTOFDEFAULT
 .endd
 
 tls_require_ciphers = ECDSA:RSA:!COMPLEMENTOFDEFAULT
 .endd
 

+.new
+For TLS version 1.3 the control available is less fine-grained
+and Exim does not provide access to it at present.
+The value of the &%tls_require_ciphers%& option is ignored when
+TLS version 1.3 is negotiated.
+
+As of writing the library default cipher suite list for TLSv1.3 is
+.code
+TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256
+.endd
+.wen
+

 
 .section "Requiring specific ciphers or other parameters in GnuTLS" &&&
          "SECTreqciphgnu"
 
 .section "Requiring specific ciphers or other parameters in GnuTLS" &&&
          "SECTreqciphgnu"


@@ -31148,6 +31201,15 @@ connection, HELO, or MAIL).
 The main use of these variables is expected to be to distinguish between
 rejections of MAIL and rejections of RCPT in callouts.
 
 The main use of these variables is expected to be to distinguish between
 rejections of MAIL and rejections of RCPT in callouts.
 

+.new
+The above variables may also be set after a &*successful*&
+address verification to:
+
+.ilist
+&%random%&: A random local-part callout succeeded
+.endlist
+.wen
+

 
 
 
 
 
 


@@ -39037,7 +39099,7 @@ tag value.  Note that Exim does not check the value.
 This option sets the canonicalization method used when signing a message.
 The DKIM RFC currently supports two methods: "simple" and "relaxed".
 The option defaults to "relaxed" when unset. Note: the current implementation
 This option sets the canonicalization method used when signing a message.
 The DKIM RFC currently supports two methods: "simple" and "relaxed".
 The option defaults to "relaxed" when unset. Note: the current implementation

-only supports using the same canonicalization method for both headers and body.
+only supports signing with the same canonicalization method for both headers and body.

 
 .option dkim_strict smtp string&!! unset
 This  option  defines  how  Exim  behaves  when  signing a message that
 
 .option dkim_strict smtp string&!! unset
 This  option  defines  how  Exim  behaves  when  signing a message that


@@ -39067,26 +39129,44 @@ If a '+' prefix if used, all headers that are present with this name
 will be signed, and one signature added for a missing header with the
 name will be appended.
 
 will be signed, and one signature added for a missing header with the
 name will be appended.
 

+.new
+.option dkim_timestamps smtp integer&!! unset
+This option controls the inclusion of timestamp information in the signature.
+If not set, no such information will be included.
+Otherwise, must be an unsigned number giving an offset in seconds from the current time
+for the expiry tag
+(eg. 1209600 for two weeks);
+both creation (t=) and expiry (x=) tags will be included.
+
+RFC 6376 lists these tags as RECOMMENDED.
+.wen
+

 
 .section "Verifying DKIM signatures in incoming mail" "SECDKIMVFY"
 .cindex "DKIM" "verification"
 
 
 .section "Verifying DKIM signatures in incoming mail" "SECDKIMVFY"
 .cindex "DKIM" "verification"
 

-Verification of DKIM signatures in SMTP incoming email is implemented via the
-&%acl_smtp_dkim%& ACL. By default, this ACL is called once for each
+.new
+Verification of DKIM signatures in SMTP incoming email is done for all
+messages for which an ACL control &%dkim_disable_verify%& has not been set.
+.cindex authentication "expansion item"
+Performing verification sets up information used by the
+&$authresults$& expansion item.
+.wen
+
+.new The results of that verification are then made available to the
+&%acl_smtp_dkim%& ACL, &new(which can examine and modify them).
+By default, this ACL is called once for each

 syntactically(!) correct signature in the incoming message.
 A missing ACL definition defaults to accept.
 If any ACL call does not accept, the message is not accepted.
 If a cutthrough delivery was in progress for the message, that is
 summarily dropped (having wasted the transmission effort).
 
 syntactically(!) correct signature in the incoming message.
 A missing ACL definition defaults to accept.
 If any ACL call does not accept, the message is not accepted.
 If a cutthrough delivery was in progress for the message, that is
 summarily dropped (having wasted the transmission effort).
 

-To evaluate the signature in the ACL a large number of expansion variables
+To evaluate the &new(verification result) in the ACL
+a large number of expansion variables

 containing the signature status and its details are set up during the
 runtime of the ACL.
 
 containing the signature status and its details are set up during the
 runtime of the ACL.
 

-.cindex authentication "expansion item"
-Performing verification sets up information used by the
-&$authresults$& expansion item.
-

 Calling the ACL only for existing signatures is not sufficient to build
 more advanced policies. For that reason, the global option
 &%dkim_verify_signers%&, and a global expansion variable
 Calling the ACL only for existing signatures is not sufficient to build
 more advanced policies. For that reason, the global option
 &%dkim_verify_signers%&, and a global expansion variable


@@ -39234,6 +39314,12 @@ strict enforcement should code the check explicitly.
 The number of signed body bytes. If zero ("0"), the body is unsigned. If no
 limit was set by the signer, "9999999999999" is returned. This makes sure
 that this variable always expands to an integer value.
 The number of signed body bytes. If zero ("0"), the body is unsigned. If no
 limit was set by the signer, "9999999999999" is returned. This makes sure
 that this variable always expands to an integer value.

+.new
+&*Note:*& The presence of the signature tag specifying a signing body length
+is one possible route to spoofing of valid DKIM signatures.
+A paranoid implementation might wish to regard signature where this variable
+shows less than the "no limit" return as being invalid.
+.wen

 
 .vitem &%$dkim_created%&
 UNIX timestamp reflecting the date and time when the signature was created.
 
 .vitem &%$dkim_created%&
 UNIX timestamp reflecting the date and time when the signature was created.