Reported by Christopher Allan Webber <cwebber@dustycloud.org>
Co-authored-by: Ludovic Courtès <ludo@gnu.org>
This commit adds protection to Guile's REPL servers against HTTP
inter-protocol exploitation attacks, a scenario whereby an attacker can,
via an HTML page, cause a web browser to send data to TCP servers
listening on a loopback interface or private network. See
<https://en.wikipedia.org/wiki/Inter-protocol_exploitation> and
<https://www.jochentopf.com/hfpa/hfpa.pdf>, The HTML Form Protocol
Attack (2001) by Tochen Topf <jochen@remote.org>.
Here we add a procedure to 'before-read-hook' that looks for a possible
HTTP request-line in the first line of input from the client socket. If
present, the socket is drained and closed, and a loud warning is written
to stderr (POSIX file descriptor 2).
* module/system/repl/server.scm: Add 'maybe-check-for-http-request'
to 'before-read-hook' when this module is loaded.
(with-temporary-port-encoding, with-saved-port-line+column)
(drain-input-and-close, permissive-http-request-line?)
(check-for-http-request, guard-against-http-request)
(maybe-check-for-http-request): New procedures.
(serve-client): Use 'guard-against-http-request'.
* module/system/repl/coop-server.scm (start-repl-client): Use
'guard-against-http-request'.
* doc/ref/guile-invoke.texi (Command-line Options): In the description
of the --listen option, make the security warning more prominent.
Mention the new protection added here. Recommend using UNIX domain
sockets for REPL servers. "a path to" => "the file name of".
Modified-by: Mark H Weaver <mhw@netris.org>
* module/system/repl/coop-server.scm: New module.
* module/system/repl/repl.scm (start-repl): Extract body to start-repl*.
(start-repl*): New procedure.
(run-repl): Extract body to run-repl*.
(run-repl*): New procedure.
* module/system/repl/server.scm (run-server): Extract body to
run-server*.
(run-server*): New procedure.
* doc/ref/api-evaluation.texi (Cooperative REPL Servers): New node.
* module/Makefile.am (SYSTEM_SOURCES): Add system/repl/coop-server.scm.
