From mboxrd@z Thu Jan 1 00:00:00 1970 From: Helge Deller Subject: Re: [RFC] API to modify /proc/sys/net/ipv4/ip_local_reserved_ports Date: Thu, 17 May 2012 23:18:18 +0200 Message-ID: <4FB56B1A.6010208@gmx.de> References: <4F5BE563.9050506@gmx.de> <4F5FAF28.5030205@gmx.de> <4F611835.4080904@gmx.de> <4F7CADE8.3060205@gmx.de> <1333960981.414.24.camel@cr0> <4F84A06F.3090808@gmx.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Cong Wang , Octavian Purdila , netdev@vger.kernel.org, David Miller , Andrew Morton , Frank Danapfel , Laszlo Ersek , shemminger@vyatta.com To: "Eric W. Biederman" Return-path: Received: from mailout-de.gmx.net ([213.165.64.22]:52857 "HELO mailout-de.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1755167Ab2EQVSY (ORCPT ); Thu, 17 May 2012 17:18:24 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On 04/11/2012 12:13 AM, Eric W. Biederman wrote: > Helge Deller writes: > >> On 04/09/2012 10:43 AM, Cong Wang wrote: >>> On Wed, 2012-04-04 at 22:24 +0200, Helge Deller wrote: >>>> I would like to follow up on my last patch series to be able to modify >>>> the contents of the /proc/sys/net/ipv4/ip_local_reserved_ports port list >>>> from userspace. >>>> >>>> My last patch (https://lkml.org/lkml/2012/3/10/187) was based on >>>> modifications to the proc interface, which - based on the feedback here >>>> on the list - seemed to not be the right way to go (although I personally >>>> still like the idea very much :-)). >>>> >>>> Anyway, with this RFC I would like to get feedback about a new proposed >>>> API and attached kernel patch. >>>> >>>> The idea is to introduce a new value for get/setsockopt() >>>> named SO_RESERVED_PORTS to get/set the ip_local_reserved_ports >>>> bitmap via standard get/setsockopt() syscalls. >>>> As far as I understand this seems to be similiar to how iptables works. >>>> >>>> An untested kernel patch for review and feedback is attached below. >>>> >>>> In userspace it then would be possible to write a new tool or to extend >>>> for example the "ip" tool to accept commands like: >>>> $> ip reserved_ports add 100-2000 >>>> $> ip reserved_ports remove 50-60 >>>> $> ip reserved_ports list (to show current reserved port list) >>>> >>>> This userspace tool could then read the port bitmap from kernel via >>>> a) socket(PF_INET, SOCK_RAW, IPPROTO_RAW) >>>> b) getsockopt(3, SOL_SOCKET, SO_RESERVED_PORTS,) >>>> and write back the results after modification via >>>> c) setsockopt(3, SOL_SOCKET, SO_RESERVED_PORTS,) >>>> >>>> Would that be an acceptable solution? >>> Hmm, it is indeed that bitmap fits for syscall rather than /proc file. >>> >>> But it seems that using getsockopt()/setsockopt() makes it like it is a >>> per-socket setting, actually it is a system-wide setting. >> Yes, that's the reason why I used SOL_SOCKET which configures at least >> a few system-wide settings too. >> >>> So I am >>> wondering if exporting a binary /proc file for this is a better >>> solution. >> Yeah - that's another solution, but (65536 ports)/(8 bits per byte) = 8 KByte, >> so we >> may again hit the 4k limit of /proc (unless you do binary reads which should >> be done with a binary /proc-entry anyway). >> >> Again, I'm open to develop any kind of solution which would get an OK >> here. > > Just looking at proc_do_large_bitmap, it does appear that there is a > very local 4k limit on writes. > > Can you please just modify proc_do_large_bitmap so that there is not a > 4k limit on writes. Ideally the code would just read another 4k from > userspace when it is getting close to the end of it's 4k buffer, or > perhaps we just read everything directly from userspace and run slowly. Hi Eric, sorry for the very late reply. Yes, you are right- this is only a local 4K limit. Increasing it allowed me to write more ports at once. With your tips I was now able to build a simple solution which fits my needs. Based on standard tools like echo and dd (with the seek option) I can block all ports which I need. Nevertheless, the current kernel interface is not very flexible. So, my proposal for a new interface (with tools) still stands. I just need and advise what would be acceptable. Without any advise I will just leave everything as is (since I'm now fine with it). Helge