Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751741AbbEASnD (ORCPT ); Fri, 1 May 2015 14:43:03 -0400 Received: from mail-ig0-f174.google.com ([209.85.213.174]:34174 "EHLO mail-ig0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751233AbbEASm7 (ORCPT ); Fri, 1 May 2015 14:42:59 -0400 Message-ID: <1430505777.3711.135.camel@edumazet-glaptop2.roam.corp.google.com> Subject: Re: [PATCH] Allow TCP connections to cache SYN packet for userspace inspection From: Eric Dumazet To: Eric B Munson Cc: "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy , netdev@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 01 May 2015 11:42:57 -0700 In-Reply-To: <1430502237-5619-1-git-send-email-emunson@akamai.com> References: <1430502237-5619-1-git-send-email-emunson@akamai.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1914 Lines: 43 On Fri, 2015-05-01 at 13:43 -0400, Eric B Munson wrote: > In order to enable policy decisions in userspace, the data contained in > the SYN packet would be useful for tracking or identifying connections. > Only parts of this data are available to userspace after the hand shake > is completed. This patch exposes a new setsockopt() option that will, > when used with a listening socket, ask the kernel to cache the skb > holding the SYN packet for retrieval later. The SYN skbs will not be > saved while the kernel is in syn cookie mode. > > The same option will ask the kernel for the packet headers when used > with getsockopt() with the socket returned from accept(). The cached > packet will only be available for the first getsockopt() call, the skb > is consumed after the requested data is copied to userspace. Subsequent > calls will return -ENOENT. Because of this behavior, getsockopt() will > return -E2BIG if the caller supplied a buffer that is too small to hold > the skb header. > > Signed-off-by: Eric B Munson > Cc: Alexey Kuznetsov > Cc: James Morris > Cc: Hideaki YOSHIFUJI > Cc: Patrick McHardy > Cc: netdev@vger.kernel.org > Cc: linux-api@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > --- We have a similar patch here at Google, but we do not hold one skb and dst per saved syn. That can be ~4KB for some drivers. Only a kmalloc() with the needed part (headers), usually less than 128 bytes. We store the length in first byte of this allocation. This has a huge difference if you want to have ~4 million request socks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/