Subject: [PATCH] * gnu: endlessh: new service

From: Joshua Branson <[email-masked]>
Date: Fri, 30 Sep 2022 13:03:01 -0400

From: Nicolò Balzarotti <[email-masked]>

Here is an attempted merger of patch 1 and 2.  I hope that it applies
cleanly to master, but if it does not, please let me know!

Thanks!

Joshua

* gnu/services/ssh.scm: Add endlessh service
endlessh-configuration>): New record type.
(endlessh-config->conf, endlessh-shepherd-service, endlessh-service-type): New procedures.

* doc/guix.texi: added documnetation for the endlessh service.
---
 doc/guix.texi        | 60 ++++++++++++++++++++++++++++++++++++
 gnu/services/ssh.scm | 73 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 133 insertions(+)

diff --git a/doc/guix.texi b/doc/guix.texi
index 99f8ba6c54..9a1e2801dd 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -20393,6 +20393,66 @@ may cause undefined behaviour.
 @end table
 @end deftp
 
+@cindex Endlessh
+@deffn {Scheme Variable} endlessh-service-type
+This is the type for the @uref{https://github.com/skeeto/endlessh,
+Endlessh} service, which is an ssh tarbit.  It delays ssh clients for
+days at a time by @emph{very slowly} sending a random and endless SSH
+banner.  The smart hacker will run endlessh on port 22, and let crackers
+get stuck in this tarpit.  This lets your real ssh server run more
+securely on a non-standard port.
+
+For example:
+
+@lisp
+(service endlessh-service-type
+  (endlessh-configuration
+    (port-number 22)))
+@end lisp
+
+@end deffn
+
+@deftp {Data Type} endlessh-configuration
+Data type representing the configuration for @code{endlessh-service}.
+@table @asis
+@item @code{package} (default: @var{endlessh})
+@code{endlessh} package to use.
+
+@item @code{bind-family} (default: @code{'(ipv4 ipv6)})
+This specifies if endlessh should use ipv4 and/or ipv6.
+
+@item @code{delay} (default: @code{10000})
+The endless banner is sent one line at a time. This is the delay
+in milliseconds between individual lines.
+
+@item @code{length} (default: @code{32})
+The length of each line is randomized. This controls the maximum length
+of each line. Shorter lines may keep clients on for longer if they give
+up after a certain number of bytes.
+
+@item @code{max-clients} (default: @code{4096})
+Maximum number of connections to accept at a time. Connections beyond
+this are not immediately rejected, but will wait in the queue.
+
+@item @code{port-number} (default: @code{2222})
+The port on which to listen for new SSH connections.  Most users who
+want to use endlessh as intended should set this port number to
+@code{22}.
+
+@item @code{log-level} (default: @code{0})
+Set the detail level for the log.
+@table @asis
+@item  0 = Quiet
+@item  1 = Standard, useful log messages
+@item  2 = Very noisy debugging information
+@end table
+
+@item @code{syslog} (default: @code{#f})
+Print diagnostics to syslog instead of standard output
+
+@end table
+@end deftp
+
 @cindex WebSSH
 @deffn {Scheme Variable} webssh-service-type
 This is the type for the @uref{https://webssh.huashengdun.org/, WebSSH}
diff --git a/gnu/services/ssh.scm b/gnu/services/ssh.scm
index 72e7183590..2e547b63cd 100644
--- a/gnu/services/ssh.scm
+++ b/gnu/services/ssh.scm
@@ -58,6 +58,10 @@ (define-module (gnu services ssh)
             autossh-configuration?
             autossh-service-type
 
+            endlessh-configuration
+            endlessh-configuration?
+            endlessh-service-type
+
             webssh-configuration
             webssh-configuration?
             webssh-service-type
@@ -802,6 +806,75 @@ (define autossh-service-type
                              autossh-service-activation)))
    (default-value (autossh-configuration))))
 
+
+;;;
+;;; Endlessh.
+;;;
+
+(define-record-type* <endlessh-configuration>
+  endlessh-configuration make-endlessh-configuration
+  endlessh-configuration?
+  ;; list of two symbols, allowed values are ipv4, ipv6 or both
+  (bind-family endlessh-configuration-bind-family (default '(ipv4 ipv6)))
+  ;; integer
+  (delay endlessh-configuration-delay (default 10000))
+  ;; integer
+  ;; Must be in the range
+  (length endlessh-configuration-length (default 32))
+  ;; integer
+  (max-clients endlessh-configuration-max-clients (default 4096))
+  ;; integer
+  (port-number endlessh-configuration-port-number (default 2222))
+  ;; integer
+  ;; Allowed values are 0, 1 and 2
+  (log-level endlessh-configuration-log-level (default 0)))
+
+(define (endlessh-config->conf config)
+  "Convert the CONFIG of type <endlessh-config> to a config file."
+  (let* ((family (endlessh-configuration-bind-family config))
+	 (ipv4 (member 'ipv4 family))
+	 (ipv6 (member 'ipv6 family))
+	 (port (endlessh-configuration-port-number config))
+	 (delay (endlessh-configuration-delay config))
+	 (length (endlessh-configuration-length config))
+	 (log-level (endlessh-configuration-log-level config))
+	 (max-clients (endlessh-configuration-max-clients config))
+	 (bind
+	  ;; check if both are true (0), or only one of them is present
+	  (if (not (and (equal? ipv4 ipv6) ipv4))
+	      (if ipv4 4
+		  (if ipv6 6
+		      (throw 'endlessh-error
+			     "bind-family must contain at least one value")))
+	      0)))
+    (mixed-text-file "endlessh.conf"
+		     "# Generated by 'endlessh-config'.\n\n"
+		     "Port " (number->string port) "\n"
+		     "Delay " (number->string delay) "\n"
+		     "MaxLineLength " (number->string length) "\n"
+		     "MaxClients " (number->string max-clients) "\n"
+		     "LogLevel " (number->string log-level) "\n"
+		     "BindFamily " (number->string bind) "\n")))
+
+(define (endlessh-shepherd-service config)
+  (shepherd-service
+   (documentation "Run endlessh tarpit server.")
+   (provision '(endlessh))
+   (start #~(make-forkexec-constructor
+	     (list #$(file-append endlessh "/bin/endlessh")
+		   "-f" #$(endlessh-config->conf config))))
+   (stop  #~(make-kill-destructor))))
+
+(define endlessh-service-type
+  (service-type
+   (name 'endlessh)
+   (description "Run endlessh tarpit server.")
+   (extensions
+    (list (service-extension shepherd-root-service-type
+                             (compose list endlessh-shepherd-service))))
+   (default-value (endlessh-configuration))))
+
+
 
 ;;;
 ;;; WebSSH
-- 
2.37.3