From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org
X-Spam-Level: 
X-Spam-Status: No, score=0.2 required=5.0 tests=DKIM_INVALID,DKIM_SIGNED
	autolearn=no autolearn_force=no version=3.4.4
Received: (qmail 12915 invoked from network); 16 Nov 2022 03:48:57 -0000
Received: from 9front.inri.net (168.235.81.73)
  by inbox.vuxu.org with ESMTPUTF8; 16 Nov 2022 03:48:57 -0000
Received: from mail.posixcafe.org ([45.76.19.58]) by 9front; Tue Nov 15 22:45:14 -0500 2022
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=posixcafe.org;
	s=20200506; t=1668570444;
	h=from:from:reply-to:subject:subject:date:date:message-id:message-id:
	 to:to:cc:mime-version:mime-version:content-type:content-type:
	 content-transfer-encoding:content-transfer-encoding;
	bh=yBhtyODl4ohMLauCvg2/EF0CbB3xYN3FYBrpJHgKOK4=;
	b=I6rYYnYqYTrCLlgRx4QEv7yed894gKxrRy8Eb9ksneAAGpqkRR5bRLvrGvAa8uO9z7t1ZF
	FUu6ywuT181TXjWNDROIwZGqNnPR3XTV5UlfZsdxaYo+G8EqpsH17xBPro+Z8YFPPulCV3
	qgYl8V4CNDWoSBPbcDXLo+1Bh1Lvy84=
Received: from [192.168.168.200] (161-97-205-25.mynextlight.net [161.97.205.25])
	by mail.posixcafe.org (OpenSMTPD) with ESMTPSA id 6d577499 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO)
	for <9front@9front.org>;
	Tue, 15 Nov 2022 21:47:24 -0600 (CST)
Message-ID: <fd9f3ff2-645c-9ff2-22d0-7e218dc88ed8@posixcafe.org>
Date: Tue, 15 Nov 2022 20:42:52 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.4.2
Content-Language: en-US
To: 9front@9front.org
From: Jacob Moody <moody@mail.posixcafe.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
List-ID: <9front.9front.org>
List-Help: <http://lists.9front.org>
X-Glyph: ➈
X-Bullshit: social cloud markup event-oriented frontend 
Subject: [9front] [PITCH] ip/null
Reply-To: 9front@9front.org
Precedence: bulk

As I play around more with 9front as my router, I found myself reaching for some
kind of 'firewall'. I find that we already have a pretty good interface in the kernel
in the form of ipmux. But there isn't too many ways of making use of it as is. I hacked up
something quick to just drop packets matching a filter on to the floor. If others find it
useful I can make up a man page and present again with a bit more polish.

Some examples:
# Drop inbound private range
ip/null 'ifc=my.external.ip;dst=192.168.0.0&255.255.0.0|10.0.0.0&255.0.0.0'

# google verboden
ip/null 'ifc=my.internal.ip;dst=8.8.8.8;src=192.168.0.0&255.255.0.0'

thanks,
moody

--- /dev/null
+++ b//sys/src/cmd/ip/null.c
@@ -1,0 +1,36 @@
+#include <u.h>
+#include <libc.h>
+
+void
+usage(void)
+{
+	fprint(2, "usage: %s filter\n", argv0);
+	exits("usage");
+}
+
+void
+main(int argc, char **argv)
+{
+	char buf[64 * 1024];
+	int fd;
+
+	ARGBEGIN{
+	default:
+		usage();
+		break;
+	}ARGEND
+	if(argc < 1)
+		usage();
+
+	fd = dial(smprint("ipmux!%s", argv[0]), nil, nil, nil);
+	if(fd < 0)
+		sysfatal("dial: %r");
+
+	for(;;)
+		switch(read(fd, buf, sizeof buf)){
+		case -1:
+			sysfatal("read: %r");
+		case 0:
+			return;
+		}
+}