X-Git-Url: https://git.exim.org/users/heiko/exim.git/blobdiff_plain/532be4499552dfab0e3173f7d3e85c81e1496147..1e83d68b72d24d6255d2e78facbe01656515ab4f:/doc/doc-docbook/spec.xfpt?ds=inline diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index dd8db2367..bbc3949c6 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -1,4 +1,4 @@ -. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.83 2010/06/07 07:09:10 pdp Exp $ +. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.88 2010/06/14 18:51:09 pdp Exp $ . . ///////////////////////////////////////////////////////////////////////////// . This is the primary source of the Exim Manual. It is an xfpt document that is @@ -1896,6 +1896,8 @@ given in chapter &<>&. .section "Use of tcpwrappers" "SECID27" .cindex "tcpwrappers, building Exim to support" .cindex "USE_TCP_WRAPPERS" +.cindex "TCP_WRAPPERS_DAEMON_NAME" +.cindex "tcp_wrappers_daemon_name" Exim can be linked with the &'tcpwrappers'& library in order to check incoming SMTP calls using the &'tcpwrappers'& control files. This may be a convenient alternative to Exim's own checking facilities for installations that are @@ -1910,14 +1912,17 @@ USE_TCP_WRAPPERS=yes CFLAGS=-O -I/usr/local/include EXTRALIBS_EXIM=-L/usr/local/lib -lwrap .endd -in &_Local/Makefile_&. The name to use in the &'tcpwrappers'& control files is -&"exim"&. For example, the line +in &_Local/Makefile_&. The daemon name to use in the &'tcpwrappers'& control +files is &"exim"&. For example, the line .code exim : LOCAL 192.168.1. .friendly.domain.example .endd in your &_/etc/hosts.allow_& file allows connections from the local host, from the subnet 192.168.1.0/24, and from all hosts in &'friendly.domain.example'&. -All other connections are denied. Consult the &'tcpwrappers'& documentation for +All other connections are denied. The daemon name used by &'tcpwrappers'& +can be changed at build time by setting TCP_WRAPPERS_DAEMON_NAME in +in &_Local/Makefile_&, or by setting tcp_wrappers_daemon_name in the +configure file. Consult the &'tcpwrappers'& documentation for further details. @@ -3179,11 +3184,20 @@ the listening daemon. .cindex "testing", "malware" .cindex "malware scan test" This debugging option causes Exim to scan the given file, -using the malware scanning framework. The option of av_scanner influences -this option, so if av_scanner's value is dependent upon an expansion then -the expansion should have defaults which apply to this invocation. Exim will -have changed working directory before resolving the filename, so using fully -qualified pathnames is advisable. This option requires admin privileges. +using the malware scanning framework. The option of &%av_scanner%& influences +this option, so if &%av_scanner%&'s value is dependent upon an expansion then +the expansion should have defaults which apply to this invocation. ACLs are +not invoked, so if &%av_scanner%& references an ACL variable then that variable +will never be populated and &%-bmalware%& will fail. + +Exim will have changed working directory before resolving the filename, so +using fully qualified pathnames is advisable. Exim will be running as the Exim +user when it tries to open the file, rather than as the invoking user. +This option requires admin privileges. + +The &%-bmalware%& option will not be extended to be more generally useful, +there are better tools for file-scanning. This option exists to help +administrators verify their Exim and AV scanner configuration. .vitem &%-bt%& .oindex "&%-bt%&" @@ -3317,25 +3331,20 @@ name, but it can be a colon-separated list of names. In this case, the first file that exists is used. Failure to open an existing file stops Exim from proceeding any further along the list, and an error is generated. -When this option is used by a caller other than root or the Exim user, and the -list is different from the compiled-in list, Exim gives up its root privilege -immediately, and runs with the real and effective uid and gid set to those of -the caller. However, if ALT_CONFIG_ROOT_ONLY is defined in -&_Local/Makefile_&, root privilege is retained for &%-C%& only if the caller of -Exim is root. - -That is, the Exim user is no longer privileged in this regard. This build-time -option is not set by default in the Exim source distribution tarbundle. -However, if you are using a &"packaged"& version of Exim (source or binary), -the packagers might have enabled it. - -Setting ALT_CONFIG_ROOT_ONLY locks out the possibility of testing a -configuration using &%-C%& right through message reception and delivery, even -if the caller is root. The reception works, but by that time, Exim is running -as the Exim user, so when it re-executes to regain privilege for the delivery, -the use of &%-C%& causes privilege to be lost. However, root can test reception -and delivery using two separate commands (one to put a message on the queue, -using &%-odq%&, and another to do the delivery, using &%-M%&). +When this option is used by a caller other than root, and the list is different +from the compiled-in list, Exim gives up its root privilege immediately, and +runs with the real and effective uid and gid set to those of the caller. +However, if a TRUSTED_CONFIG_PREFIX_LIST file is defined in &_Local/Makefile_&, +root privilege is retained for any configuration file which matches a prefix +listed in that file. + +Leaving TRUSTED_CONFIG_PREFIX_LIST unset precludes the possibility of testing +a configuration using &%-C%& right through message reception and delivery, +even if the caller is root. The reception works, but by that time, Exim is +running as the Exim user, so when it re-executes to regain privilege for the +delivery, the use of &%-C%& causes privilege to be lost. However, root can +test reception and delivery using two separate commands (one to put a message +on the queue, using &%-odq%&, and another to do the delivery, using &%-M%&). If ALT_CONFIG_PREFIX is defined &_in Local/Makefile_&, it specifies a prefix string with which any file named in a &%-C%& command line option @@ -4487,17 +4496,21 @@ existing file in the list. .cindex "configuration file" "ownership" .cindex "ownership" "configuration file" The run time configuration file must be owned by root or by the user that is -specified at compile time by the EXIM_USER option, or by the user that is specified at compile time by the CONFIGURE_OWNER option (if set). The -configuration file must not be world-writeable or group-writeable, unless its -group is the one specified at compile time by the EXIM_GROUP option or by the +configuration file must not be world-writeable, or group-writeable unless its +group is the root group or the one specified at compile time by the CONFIGURE_GROUP option. &*Warning*&: In a conventional configuration, where the Exim binary is setuid to root, anybody who is able to edit the run time configuration file has an -easy way to run commands as root. If you make your mail administrators members -of the Exim group, but do not trust them with root, make sure that the run time -configuration is not group writeable. +easy way to run commands as root. If you specify a user or group in the +CONFIGURE_OWNER or CONFIGURE_GROUP options, then that user and/or any users +who are members of that group will trivially be able to obtain root privileges. + +Up to Exim version 4.72, the run time configuration file was also permitted to +be writeable by the Exim user and/or group. That has been changed in Exim 4.73 +since it offered a simple privilege escalation for any attacker who managed to +compromise the Exim user account. A default configuration file, which will work correctly in simple situations, is provided in the file &_src/configure.default_&. If CONFIGURE_FILE @@ -4513,21 +4526,23 @@ configuration. .cindex "configuration file" "alternate" A one-off alternate configuration can be specified by the &%-C%& command line option, which may specify a single file or a list of files. However, when -&%-C%& is used, Exim gives up its root privilege, unless called by root or the -Exim user (or unless the argument for &%-C%& is identical to the built-in value -from CONFIGURE_FILE). &%-C%& is useful mainly for checking the syntax of -configuration files before installing them. No owner or group checks are done -on a configuration file specified by &%-C%&. - -The privileged use of &%-C%& by the Exim user can be locked out by setting -ALT_CONFIG_ROOT_ONLY in &_Local/Makefile_& when building Exim. However, -if you do this, you also lock out the possibility of testing a -configuration using &%-C%& right through message reception and delivery, even -if the caller is root. The reception works, but by that time, Exim is running -as the Exim user, so when it re-execs to regain privilege for the delivery, the -use of &%-C%& causes privilege to be lost. However, root can test reception and -delivery using two separate commands (one to put a message on the queue, using -&%-odq%&, and another to do the delivery, using &%-M%&). +&%-C%& is used, Exim gives up its root privilege, unless called by root (or +unless the argument for &%-C%& is identical to the built-in value from +CONFIGURE_FILE) or matches a prefix listed in the TRUSTED_CONFIG_PREFIX_LIST +file. &%-C%& is useful mainly for checking the syntax of configuration files +before installing them. No owner or group checks are done on a configuration +file specified by &%-C%&, if root privilege has been dropped. + +Even the Exim user is not trusted to specify an arbitrary configuration file +with the &%-C%& option to be used with root privileges, unless that file is +listed in the TRUSTED_CONFIG_PREFIX_LIST file. This locks out the possibility +of testing a configuration using &%-C%& right through message reception and +delivery, even if the caller is root. The reception works, but by that time, +Exim is running as the Exim user, so when it re-execs to regain privilege for +the delivery, the use of &%-C%& causes privilege to be lost. However, root +can test reception and delivery using two separate commands (one to put a +message on the queue, using &%-odq%&, and another to do the delivery, using +&%-M%&). If ALT_CONFIG_PREFIX is defined &_in Local/Makefile_&, it specifies a prefix string with which any file named in a &%-C%& command line option must @@ -9802,7 +9817,7 @@ zero. This condition turns a string holding a true or false representation into a boolean state. It parses &"true"&, &"false"&, &"yes"& and &"no"& (case-insensitively); also positive integer numbers map to true if non-zero, -false if zero. Leading whitespace is ignored. +false if zero. Leading and trailing whitespace is ignored. All other string values will result in expansion failure. When combined with ACL variables, this expansion condition will let you @@ -9812,6 +9827,17 @@ For example: ${if bool{$acl_m_privileged_sender} ... .endd +.vitem &*bool_lax&~{*&<&'string'&>&*}*& +.cindex "expansion" "boolean parsing" +.cindex "&%bool_lax%& expansion condition" +Like &%bool%&, this condition turns a string into a boolean state. But +where &%bool%& accepts a strict set of strings, &%bool_lax%& uses the same +loose definition that the Router &%condition%& option uses. The empty string +and the values &"false"&, &"no"& and &"0"& map to false, all others map to +true. Leading and trailing whitespace is ignored. + +Note that where &"bool{00}"& is false, &"bool_lax{00}"& is true. + .vitem &*crypteq&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& .cindex "expansion" "encrypted comparison" .cindex "encrypted strings, comparing" @@ -15670,10 +15696,7 @@ If the result is any other value, the router is run (as this is the last precondition to be evaluated, all the other preconditions must be true). This option is unique in that multiple &%condition%& options may be present. -In this case, the previous statement does not quite apply: the result of each -&%condition%& option must be a string recognised by the &%bool%& expansion -operator, or failure will be forced. The effect is to "and" the conditions -together, as each must pass. +All &%condition%& options must succeed. The &%condition%& option provides a means of applying custom conditions to the running of routers. Note that in the case of a simple conditional expansion, @@ -15685,10 +15708,11 @@ Because of the default behaviour of the string expansion, this is equivalent to .code condition = ${if >{$message_age}{600}{true}{}} .endd -A multiple condition example: +A multiple condition example, which succeeds: .code condition = ${if >{$message_age}{600}} condition = ${if !eq{${lc:$local_part}}{postmaster}} +condition = foobar .endd If the expansion fails (other than forced failure) delivery is deferred. Some of the other precondition options are common special cases that could in fact @@ -33778,15 +33802,16 @@ which only root has access, this guards against someone who has broken into the Exim account from running a privileged Exim with an arbitrary configuration file, and using it to break into other accounts. .next -If ALT_CONFIG_ROOT_ONLY is defined, root privilege is retained for &%-C%& -and &%-D%& only if the caller of Exim is root. Without it, the Exim user may -also use &%-C%& and &%-D%& and retain privilege. Setting this option locks out -the possibility of testing a configuration using &%-C%& right through message -reception and delivery, even if the caller is root. The reception works, but by -that time, Exim is running as the Exim user, so when it re-execs to regain -privilege for the delivery, the use of &%-C%& causes privilege to be lost. -However, root can test reception and delivery using two separate commands. -ALT_CONFIG_ROOT_ONLY is not set by default. +If a non-trusted configuration file (i.e. the default configuration file or +one which is trusted by virtue of matching a prefix listed in the +TRUSTED_CONFIG_PREFIX_LIST file) is specified with &%-C%&, or if macros are +given with &%-D%&, then root privilege is retained only if the caller of Exim +is root. This locks out the possibility of testing a configuration using &%-C%& +right through message reception and delivery, even if the caller is root. The +reception works, but by that time, Exim is running as the Exim user, so when +it re-execs to regain privilege for the delivery, the use of &%-C%& causes +privilege to be lost. However, root can test reception and delivery using two +separate commands. .next If DISABLE_D_OPTION is defined, the use of the &%-D%& command line option is disabled. @@ -33842,11 +33867,10 @@ uid and gid in the following cases: .oindex "&%-D%&" If the &%-C%& option is used to specify an alternate configuration file, or if the &%-D%& option is used to define macro values for the configuration, and the -calling process is not running as root or the Exim user, the uid and gid are -changed to those of the calling process. -However, if ALT_CONFIG_ROOT_ONLY is defined in &_Local/Makefile_&, only -root callers may use &%-C%& and &%-D%& without losing privilege, and if -DISABLE_D_OPTION is set, the &%-D%& option may not be used at all. +calling process is not running as root, the uid and gid are changed to those of + the calling process. +However, if DISABLE_D_OPTION is defined in &_Local/Makefile_&, the &%-D%& +option may not be used at all. .next .oindex "&%-be%&" .oindex "&%-bf%&"