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| author | Laurent Bercot <ska-skaware@skarnet.org> | 2014-12-15 23:08:59 +0000 |
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| committer | Laurent Bercot <ska-skaware@skarnet.org> | 2014-12-15 23:08:59 +0000 |
| commit | e0fc82203d677a6f1e808e9a1a46176c109d89be (patch) | |
| tree | e9609209b755e3f7a8480aea86601ffe9d4ca540 /doc/s6-tcpserver-access.html | |
| download | s6-networking-e0fc82203d677a6f1e808e9a1a46176c109d89be.tar.xz | |
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diff --git a/doc/s6-tcpserver-access.html b/doc/s6-tcpserver-access.html new file mode 100644 index 0000000..7bf15a0 --- /dev/null +++ b/doc/s6-tcpserver-access.html @@ -0,0 +1,239 @@ +<html> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>s6-networking: the s6-tcpserver-access program</title> + <meta name="Description" content="s6-networking: the s6-tcpserver-access program" /> + <meta name="Keywords" content="s6-networking s6-tcpserver-access tcp access control tcprules tcpwrappers libwrap" /> + <!-- <link rel="stylesheet" type="text/css" href="http://skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">s6-networking</a><br /> +<a href="http://skarnet.org/software/">Software</a><br /> +<a href="http://skarnet.org/">skarnet.org</a> +</p> + +<h1> The <tt>s6-tcpserver-access</tt> program </h1> + +<p> +<tt>s6-tcpserver-access</tt> is a command-line TCP access +control tool, and additionally performs some fine-tuning on a +TCP socket. It is meant to be run after +<a href="s6-tcpserver.html">s6-tcpserver</a> and before +the application program on the s6-tcpserver command line, +just like tcpwrappers' <tt>tcpd</tt> program. +</p> + +<h2> Interface </h2> + +<pre> + s6-tcpserver-access [ -v <em>verbosity</em> ] [ -W | -w ] [ -D | -d ] [ -H | -h ] [ -R | -r ] [ -P | -p ] [ -l <em>localname</em> ] [ -B <em>banner</em> ] [ -t <em>timeout</em> ] [ -i <em>rulesdir</em> | -x <em>rulesfile</em> ] <em>prog...</em> +</pre> + +<ul> + <li> s6-tcpserver-access checks it is run under a UCSPI server tool +such as <a href="s6-tcpserver.html">s6-tcpserver</a>, + <a href="s6-tcpserver4.html">s6-tcpserver4</a> or + <a href="s6-tcpserver6.html">s6-tcpserver6</a>. </li> + <li> It checks that the remote end of the connection fits the +accepted criteria defined by the database contained in <em>rulesdir</em> +or <em>rulesfile</em>. If the database tells it to reject the connection, +the program exits 1. </li> + <li> It sets up a few additional environment variables. </li> + <li> It executes into <em>prog...</em>, +unless the first matching rule in the rule database +includes instructions to override <em>prog...</em>. </li> +</ul> + +<h2> Environment variables </h2> + +<p> +s6-tcpserver-access expects to inherit some environment variables from +its parent: +</p> + +<ul> + <li> PROTO: normally TCP, but could be anything else, like SSL. </li> + <li> ${PROTO}REMOTEIP: the remote address of the socket, i.e. the client's +IP address. This can be IPv4 or (if the underlying skalibs supports it) IPv6. </li> + <li> ${PROTO}REMOTEPORT: the remote port of the socket. </li> +</ul> + +<p> + Additionally, it exports the following variables before executing into +<em>prog...</em>: +</p> + +<ul> + <li> ${PROTO}LOCALIP: set to the local address of the socket. </li> + <li> ${PROTO}LOCALPORT: set to the local port of the socket. </li> + <li> ${PROTO}REMOTEINFO: normally unset, but set to the information +retrieved from ${PROTO}REMOTEIP via the IDENT protocol if the <tt>-R</tt> +option has been given. </li> + <li> ${PROTO}REMOTEHOST: set to the remote host name obtained from +a DNS lookup. Unset if the <tt>-H</tt> option has been given. </li> + <li> ${PROTO}LOCALHOST: set to the local host name obtained from a +DNS lookup. If the <tt>-l</tt> option has been given, set to +<em>localname</em> instead. </li> +</ul> + +<p> + Also, the access rules database can instruct s6-tcpserver-access to set +up, or unset, more environment variables, depending on the client address. +</p> + +<h2> Options </h2> + +<ul> + <li> <tt>-v <em>verbosity</em></tt> : be more or less verbose, i.e. +print more or less information to stderr: + <ul> + <li> 0: only log error messages. </li> + <li> 1: only log error and warning messages, and accepted connections. +This is the default. </li> + <li> 2: also log rejected connections and more warning messages. </li> + <li> 3: also log detailed warning messages from DNS and IDENT resolution. </li> + </ul> </li> + <li> <tt>-W</tt> : non-fatal. If errors happen during DNS or IDENT +resolution, the connection process is not aborted. However, incorrect or +incomplete results might still prevent a legitimate connection from being +authenticated against a DNS name. This is the default. </li> + <li> <tt>-w</tt> : fatal. Errors during DNS or IDENT resolution will +drop the connection. </li> + <li> <tt>-D</tt> : disable Nagle's algorithm. Sets the TCP_NODELAY +flag on the network socket. </li> + <li> <tt>-d</tt> : enable Nagle's algorithm. This is the default. </li> + <li> <tt>-H</tt> : disable DNS lookups for the ${PROTO}LOCALHOST and +${PROTO}REMOTEHOST environment variables. </li> + <li> <tt>-h</tt> : enable DNS lookups. This is the default. </li> + <li> <tt>-R</tt> : disable IDENT lookups for the ${PROTO}REMOTEINFO +environment variable. This is the default. </li> + <li> <tt>-r</tt> : enable IDENT lookups. This should only be done +for legacy programs that need it. </li> + <li> <tt>-P</tt> : no paranoid DNS lookups. This is the default. </li> + <li> <tt>-p</tt> : paranoid. After looking up a name for the remote +host, s6-tcpserver-access will lookup IP addresses for this name, and drop +the connection if none of the results matches the address the connection +is originating from. Note that this still does not replace real +authentication via a cryptographic protocol. </li> + <li> <tt>-l <em>localname</em></tt> : use <em>localname</em> +as the value for the ${PROTO}LOCALHOST environment variable, instead of +looking it up in the DNS. </li> + <li> <tt>-B <em>banner</em></tt> : print <em>banner</em> to +the network as soon as the connection is attempted, even before +checking client credentials. The point is to speed up network protocols +that start with a server-side message. </li> + <li> <tt>-t <em>timeout</em></tt> : set a timeout on all the +operations performed by s6-tcpserver-access. If it is not able to do +its job in <em>timeout</em> milliseconds, it will instantly exit 99. +The default is 0, meaning no such timeout. </li> + <li> <tt>-i <em>rulesdir</em></tt> : check client credentials +against a filesystem-based database in the <em>rulesdir</em> directory. </li> + <li> <tt>-x <em>rulesfile</em></tt> : check client credentials +against a <a href="http://en.wikipedia.org/wiki/Cdb_(software)">cdb</a> +database in the <em>rulesfile</em> file. <tt>-i</tt> and <tt>-x</tt> are +mutually exclusive. If none of those options is given, no credential checking will be +performed, and a warning will be emitted on every connection if +<em>verbosity</em> is 2 or more. </li> +</ul> + +<h2> Access rule checking </h2> + +<p> + s6-tcpserver-access checks its client connection against +a ruleset. This ruleset can be implemented: +</p> + +<ul> + <li> either in the filesystem as an arborescence of directories and files, +if the <tt>-i</tt> option has been given. This option is the most flexible +one: the directory format is simple enough for scripts to understand and +modify it, and the ruleset can be changed dynamically. This is practical, +for instance, for roaming users. </li> +<li> or in a <a href="http://en.wikipedia.org/wiki/Cdb_(software)">CDB +file</a>, if the <tt>-x</tt> option has been given. This option is the most +efficient one if the ruleset is static enough: a lot less system calls are +needed to perform searches in a CDB than in the filesystem. </li> +</ul> + +<p> + The exact format of the ruleset is described on the +<a href="s6-accessrules-cdb-from-fs.html">s6-accessrules-cdb-from-fs</a> page. +</p> + +<p> +s6-tcpserver-access first gets the remote address <em>ip</em> of the +client and converts it to canonical form. Then it checks it with the +<a href="libs6net/accessrules.html#ip4">s6net_accessrules_keycheck_ip46()</a> +function. In other words, it tries to match broader and broader network +prefixes of <em>ip</em>, from <tt>ip4/</tt><em>ip</em><tt>_32</tt> to +<tt>ip4/0.0.0.0_0</tt> if <em>ip</em> is v4, or from +<tt>ip6/</tt><em>ip</em><tt>/128</tt> to <tt>ip6/::_0</tt> if <em>ip</em> +is v6. If the result is: +</p> + + <li> S6NET_ACCESSRULES_ERROR: it immediately exits 111. </li> + <li> S6NET_ACCESSRULES_DENY: it immediately exits 1. </li> + <li> S6NET_ACCESSRULES_ALLOW: it grants access. </li> + <li> S6NET_ACCESSRULES_NOTFOUND: more information is needed. </li> +</ul> + +<p> + In the last case, if DNS lookups have been deactivated (<tt>-H</tt>) then access +is denied. But if s6-tcpserver-access is authorized to perform DNS lookups, +then it gets the remote name of the client, <em>remotehost</em>, and +checks it with the +<a href="libs6net/accessrules.html#reversedns">s6net_accessrules_keycheck_reversedns()</a> +function. In other words, it tries to match shorter and shorter suffixes +of <em>remotehost</em>, from <tt>reversedns/</tt><em>remotehost</em> to +<tt>reversedns/@</tt>. +This time, the connection is denied is the result is anything else than +S6NET_ACCESSRULES_ALLOW. +</p> + +<p> + Note that even if the access check succeeds, the connection can still be +denied if paranoid mode has been required (<tt>-p</tt>) and a forward DNS query +on <em>remotehost</em> does not match <em>ip</em>. +</p> + +<h2> Environment and executable modifications </h2> + +<p> + s6-tcpserver-access interprets non-empty <tt>env</tt> subdirectories +and <tt>exec</tt> files +it finds in the matching rule of the ruleset, as explained +in the <a href="s6-accessrules-cdb-from-fs.html">s6-accessrules-cdb-from-fs</a> +page. +</p> + +<ul> + <li> An <tt>env</tt> subdirectory is interpreted as if the +<a href="http://skarnet.org/software/s6/s6-envdir.html">s6-envdir</a> +command had been called before executing <em>prog</em>: the environment +is modified according to the contents of <tt>env</tt>. </li> + <li> An <tt>exec</tt> file containing <em>newprog</em> completely +bypasses the rest of s6-tcpserver-access' command line. After +environment modifications, if any, s6-tcpserver-access execs into +<tt><a href="http://skarnet.org/software/execline/execlineb.html">execlineb</a> -c <em>newprog</em></tt>. </li> +</ul> + +<h2> Notes </h2> + +<ul> + <li> s6-tcpserver-access works with +<a href="s6-tcpserver4.html">s6-tcpserver4</a>, handling IPv4 addresses, +as well as +<a href="s6-tcpserver6.html">s6-tcpserver6</a>, handling IPv6 addresses. +It will automatically detect the remote address type and match it against the +correct subdatabase. </li> + <li> s6-tcpserver-access may perform several DNS queries. For efficiency +purposes, it does as many of them as possible in parallel. However, if asked +to do an IDENT query, it does not parallelize it with DNS queries. Take +that into account when estimating a proper <em>timeout</em> value. </li> +</ul> + +</body> +</html> |