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Diffstat (limited to 'doc/s6-tlsd.html')
| -rw-r--r-- | doc/s6-tlsd.html | 193 |
1 files changed, 37 insertions, 156 deletions
diff --git a/doc/s6-tlsd.html b/doc/s6-tlsd.html index 36125d2..beeedda 100644 --- a/doc/s6-tlsd.html +++ b/doc/s6-tlsd.html @@ -20,8 +20,8 @@ <p> <tt>s6-tlsd</tt> is a program that performs the server side of -a TLS or SSL connection over an existing TCP connection, then spawns -an application. It is meant to make network communications +a TLS or SSL connection over an existing TCP connection, then execs +into an application. It is meant to make network communications secure even for applications that do not natively support TLS/SSL. </p> @@ -45,69 +45,25 @@ the options given when configuring <tt>s6-networking</tt>. <li> s6-tlsd expects to have an open TCP connection it can talk to on its stdin (for reading) and stdout (for writing). </li> - <li> It spawns <em>prog...</em> as a child process, -interposing itself between it and the network. -In other words: <em>prog</em> still reads cleartext -on its stdin and writes cleartext on its stdout, but -those will actually be pipes to <tt>s6-tlsd</tt>, which -will read ciphertext from its own stdin (the network) -and write ciphertext to its own stdout (the network). </li> - <li> It initiates the server side of a TLS/SSL handshake -over the network connection, expecting a TLS/SSL client on -the other side. </li> - <li> It manages the encryption/decryption of all the -messages between <em>prog</em> and the client. -<em>prog</em> speaks plaintext, but only ciphertext is sent -on the network. </li> - <li> When <em>prog</em> exits, <tt>s6-tlsd</tt> exits. + <li> It spawns a <a href="s6-tlsd-io.html">s6-tlsd-io</a> +child process that will be the server-side of a TLS connection, +perform the handshake (expecting a TLS client on the other side +of the network) and maintain the TLS tunnel. </li> + <li> When notified by <a href="s6-tlsd-io.html">s6-tlsd-io</a> +that the handshake has completed, s6-tlsd execs into +<em>prog...</em>. </li> </ul> <h2> Exit codes </h2> <ul> - <li> 96: error while configuring the TLS/SSL context - for instance, invalid -private key or server certificate files. </li> - <li> 97: error while setting up the TLS/SSL client engine. </li> - <li> 98: TLS/SSL error while running the engine. </li> <li> 100: wrong usage. </li> <li> 111: system call failed. </li> </ul> <p> - If the TLS/SSL connection closes cleanly, <tt>s6-tlsd</tt> -waits for <em>prog</em> to exit, then exits with an -<a href="//skarnet.org/software/execline/exitcodes.html">approximation</a> -of <em>prog</em>'s exit code. -</p> - -<h2> Protocol version and parameters </h2> - -<p> - During the TLS/SSL handshake, <tt>s6-tlsd</tt> tries the -versions of the protocol that is supported by default by the -backend, with the default algorithms and cipher suites; -the backend normally ensures that the most secure combination -is tried first, with slow degradation until the client and -the server agree. -</p> - -<ul> - <li> For BearSSL, this means use of the -<a href="https://bearssl.org/apidoc/bearssl__ssl_8h.html#a76293c81c4624c58254a62be7b2d5e79">br_ssl_server_init_full_rsa()</a> or -<a href="https://bearssl.org/apidoc/bearssl__ssl_8h.html#a592b2af27b2f6b9389aac854fb0b783a">br_ssl_server_init_full_ec()</a> -function. The supported protocol versions are described -<a href="https://bearssl.org/support.html#supported-versions">here</a>. </li> - <li> For LibreSSL, this means use of the -<a href="https://man.openbsd.org/OpenBSD-current/man3/tls_config_set_protocols.3">tls_config_set_protocols(TLS_PROTOCOLS_DEFAULT)</a> -call. </li> -</ul> - -<p> - As a server, <tt>s6-tlsd</tt> can be conservative in its -choice of protocols. It is currently not very conservative -when using the BearSSL backend; it could become more so in -the future, by defining a custom server profile that supports -only TLS-1.2 but with several algorithms and cipher suites. + If everything goes smoothly, s6-tlsd does not exit, but execs +into <em>prog...</em> instead. </p> <h2> Environment variables </h2> @@ -115,120 +71,44 @@ only TLS-1.2 but with several algorithms and cipher suites. <h3> Read </h3> <p> - <tt>s6-tlsd</tt> expects to have the following -environment variables set: -</p> - -<ul> - <li> <tt>KEYFILE</tt>: a path to the file -containing the server's private key, DER- or PEM-encoded. </li> - <li> <tt>CERTFILE</tt>: a path to the file -containing the server's certificate, DER- or PEM-encoded. -If PEM-encoded, the file can actually contain a chain -of certificates. </li> -</ul> - -<p> - If one of those variables is unset, <tt>s6-tlsd</tt> -will refuse to run. -</p> - -<p> - If you are using client certificats, <tt>s6-tlsd</tt> -also requires either one of the following variables to be set: -</p> - -<ul> - <li> <tt>CADIR</tt>: a directory where trust anchors -(i.e. root or intermediate CA certificates) can be found, -one per file, DER- or PEM-encoded. </li> - <li> <tt>CAFILE</tt>: a file containing the whole set -of trust anchors, PEM-encoded. </li> -</ul> - -<p> - If <tt>s6-tlsd</tt> is run as root, it can also read two -more environment variables, <tt>TLS_UID</tt> and <tt>TLS_GID</tt>, -which contain a numeric uid and a numeric gid; <tt>s6-tlsd</tt> -then drops its root privileges to this uid/gid after spawning -<em>prog...</em>. This ensures that the TLS/engine and the -application run with different privileges. -</p> - -<p> - Note that <em>prog...</em> -should drop its own root privileges by its own means: the -<a href="//skarnet.org/software/s6/s6-applyuidgid.html">s6-applyuidgid</a> -program is a way of doing it. If the <tt>s6-tlsd</tt> -invocation actually comes from a -<a href="s6-tlsserver.html">s6-tlsserver</a> command line, -and privilege-dropping options (<tt>-G</tt>, <tt>-g</tt>, -<tt>-u</tt> or <tt>-U</tt>) have been given to -<a href="s6-tlsserver.html">s6-tlsserver</a>, then -<a href="//skarnet.org/software/s6/s6-applyuidgid.html">s6-applyuidgid</a> -directly follows <tt>s6-tlsd</tt> on the command line, in order -to also drop the child's privileges before executing the application. -The point of that setup is: + s6-tlsd does not expect to have any particular +environment variables, but it spawns a +<a href="s6-tlsd-io.html">s6-tlsd-io</a> program that does. +So it should pay attention to the following variables: </p> <ul> - <li> To read the private key file as root </li> - <li> To run the application as a non-root user </li> - <li> To run <tt>s6-tlsd</tt> as a <em>different</em> non-root user </li> - <li> That way, even if <tt>s6-tlsd</tt>, the application, or both, -get compromised, the private key is still secure. </li> + <li> <tt>KEYFILE</tt> and <tt>CERTFILE</tt> </li> + <li> (if the -y or -Y option has been given) <tt>CADIR</tt> or <tt>CAFILE</tt> </li> + <li> <tt>TLS_UID</tt> and <tt>TLS_GID</tt> </ul> <h3> Written </h3> <p> - Unless the <tt>-Z</tt> option has been given to -<tt>s6-tlsd</tt>, <em>prog...</em> is run with all the -TLS/SSL variables <em>unset</em>: CADIR, CAFILE, -KEYFILE, CERTFILE, TLS_UID and TLS_GID. The goal is -for <tt>s6-tlsd</tt> to be, by default, as invisible -as possible. + By default, <em>prog...</em> is run with all these +variables <em>unset</em>: CADIR, CAFILE, +KEYFILE, CERTFILE, TLS_UID and TLS_GID. They're passed to +the <a href="s6-tlsd-io.html">s6-tlsd-io</a> child but +not to <em>prog...</em>. +The <tt>-Z</tt> option prevents that behaviour. </p> -<h2> SSL close handling </h2> - <p> - If <em>prog</em> initiates the end of the session by sending -EOF, there are two ways for the TLS/SSL layer to handle it. + However, <em>prog...</em> is run with the following additional +environment variables: </p> <ul> - <li> It can send a <tt>close_notify</tt> alert, and wait for -an acknowledgement from the peer, at which point the connection -is closed. The advantage of this setup is that it is secure -even when the application protocol is not auto-terminated, i.e. -when it does not know when its data stops. Old protocols such -as HTTP-0.9 are in this case. The drawback of this setup is -that it breaks full-duplex: once a peer has sent the -<tt>close_notify</tt>, it must discard all the incoming -records that are not a <tt>close_notify</tt> from the -other peer. So if a client sends EOF while it is still -receiving data from the server, the connection closes -immediately and the data can be truncated. </li> - <li> It can simply transmit the EOF, shutting down -half the TCP connection, and wait for the EOF back. -The advantage of this setup is that it maintains -full-duplex: a client can send EOF after its initial -request, and still receive a complete answer from the -server. The drawback is that it is insecure when the application -protocol is not auto-terminated. </li> + <li> <tt>SSL_PROTOCOL</tt> contains the protocol version: +TLSv1, TLSv1.1, TLSv1.2... </li> + <li> <tt>SSL_CIPHER</tt> contains the name of the cipher +used. </li> + <li> More similar environment variables containing information +about the connection may be added in the future. </li> </ul> -<p> - Nowadays (2017), most protocols are auto-terminated, so -it is not dangerous anymore to use EOF tranmission, and that -is the default for <tt>s6-tlsd</tt>. Nevertheless, by -using the <tt>-S</tt> option, you can -force it to use the <tt>close_notify</tt> method if your -application requires it to be secure. -</p> - -<h2> <tt>s6-tlsd</tt> options </h2> +<h2> Options </h2> <ul> <li> <tt>-v <em>verbosity</em></tt> : Be more or less @@ -236,10 +116,11 @@ verbose. Default for <em>verbosity</em> is 1. 0 is quiet, 2 is verbose, more than 2 is debug output. This option currently has no effect. </li> <li> <tt>-Z</tt> : do not clean the environment of -<tt>s6-tlsd</tt>-related variables before spawning <em>prog...</em>. </li> +the variables used by <a href="s6-tlsd-io.html">s6-tlsd-io</a> +before execing <em>prog...</em>. </li> <li> <tt>-z</tt> : clean the environment of -<tt>s6-tlsd</tt>-related variables before spawning <em>prog...</em>. -This is the default. </li> +the variables used by <a href="s6-tlsd-io.html">s6-tlsd-io</a> +before execing <em>prog...</em>. This is the default. </li> <li> <tt>-S</tt> : send a <tt>close_notify</tt> alert and break the connection when <em>prog</em> sends EOF. </li> <li> <tt>-s</tt> : transmit EOF by half-closing the TCP |