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Date: Mon, 11 Dec 2023 13:00:47 -0600
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From: Jacob Moody <moody@posixcafe.org>
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X-Bullshit: progressive overflow-preventing wrapper pipelining-oriented solution 
Subject: Re: [9front] [PITCH] ip/null
Reply-To: 9front@9front.org
Precedence: bulk

This as obsoleted by cinap's aux/dial(1).
It functionally works the same here except you would
need an explicit direction to /dev/null.

ie.

aux/dial 'ipmux!ifc=my.external.ip;dst=192.168.0.0&255.255.0.0|10.0.0.0&255.0.0.0' > /dev/null

On 12/11/23 12:54, unobe@cpan.org wrote:
> FWIW, I haven't seen anyone else comment on this, but I like it.
> 
> Quoth 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;
>> +		}
>> +}
>