[9front] [PITCH] ip/null

[Jacob Moody <moody@mail.posixcafe.org>]

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;
+		}
+}