Date: Tue, 9 Jul 2013 06:15:56 -0600 (MDT) From: Warren Block <wblock@wonkity.com> To: Gabor Pali <pgj@FreeBSD.org> Cc: svn-doc-head@freebsd.org, svn-doc-all@freebsd.org, doc-committers@freebsd.org Subject: Re: svn commit: r42215 - head/en_US.ISO8859-1/htdocs/news/status Message-ID: <alpine.BSF.2.00.1307090606520.42925@wonkity.com> In-Reply-To: <201307090848.r698m8Uq018589@svn.freebsd.org> References: <201307090848.r698m8Uq018589@svn.freebsd.org>
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On Tue, 9 Jul 2013, Gabor Pali wrote: > Author: pgj > Date: Tue Jul 9 08:48:08 2013 > New Revision: 42215 > URL: http://svnweb.freebsd.org/changeset/doc/42215 > > Log: > - Add a Q2 report on improved TCP SYN cookies > > Submitted by: andre > > Modified: > head/en_US.ISO8859-1/htdocs/news/status/report-2013-04-2013-06.xml > > Modified: head/en_US.ISO8859-1/htdocs/news/status/report-2013-04-2013-06.xml > ============================================================================== > --- head/en_US.ISO8859-1/htdocs/news/status/report-2013-04-2013-06.xml Tue Jul 9 08:33:48 2013 (r42214) > +++ head/en_US.ISO8859-1/htdocs/news/status/report-2013-04-2013-06.xml Tue Jul 9 08:48:08 2013 (r42215) > @@ -18,7 +18,7 @@ > > <!-- XXX: keep updating the number of entries --> > <p>Thanks to all the reporters for the excellent work! This report > - contains 28 entries and we hope you enjoy reading it.</p> > + contains 29 entries and we hope you enjoy reading it.</p> > > <!-- XXX: set date for the next set of submissions --> > <p>The deadline for submissions covering between July and September 2013 > @@ -1579,4 +1579,84 @@ functionality through <tt>pkg(8)</tt>.</ > and <tt>CAP_RECV_RIGHTS</tt>.</task> > </help> > </project> > + > + <project cat='kern'> > + <title>Improved TCP SYN Cookies</title> > + > + <contact> > + <person> > + <name> > + <given>Andre</given> > + <common>Oppermann</common> > + </name> > + <email>andre@FreeBSD.org</email> > + </person> > + </contact> > + > + <links> > + <url href="http://docs.freebsd.org/cgi/getmsg.cgi?fetch=28838+0+current/freebsd-net">Description</url>; > + <url href="http://people.freebsd.org/~andre/syncookie-20130708.diff">Patch</url>; > + </links> > + > + <body> > + <p>We have had a SYN cookie implementation for quite some time now > + but it has some limitations with current realities for window > + scaling and SACK encoding the in the few available bits.</p> > + > + <p>This patch updates and improves SYN cookies mainly by:</p> > + > + <ol> > + <li>Encoding of MSS, WSCALE (window scaling) and SACK into the > + ISN (initial sequence number) without the use of timestamp > + bits.</li> > + > + <li>Switching to the very fast and cryptographically strong > + SipHash-2-4 hash MAC algorithm to protect the SYN cookie > + against forgery.</li> > + </ol> > + > + <p>The common parameters used on TCP sessions have changed quite a > + bit since SYN cookies very invented some 17 years ago. Today we s/very/were/ > + have a lot more bandwidth which makes the use window scaling s/the use/use of/ > + almost mandatory. Also SACK has become standard as it makes > + recovering from packet loss much more efficient.</p> > + > + <p>The original SYN cookies method only stored an indexed MSS > + values in the cookie. This obviously is not sufficient anymore s/values/value/ s/anymore/any more/ > + and breaks in the presence of WSCALE. WSCALE information is > + only exchanged during SYN and SYN-ACK. If we cannot keep track > + of it then we severely underestimate the available send or > + receive window, compounded with the fact that with large window > + scaling the window size information on the TCP segment header > + would be even lower numerically.</p> > + > + <p>A number of years back SYN cookies have been extended to store s/back SYN/back, SYN/ s/have been/were/ > + the additional state in the TCP timestamp fields, if available > + on a connection. It has been adopted by Linux as well. While > + timestamps are common among the BSD, Linux and other Unix > + systems, Windows never enabled them by default, thus they are > + not present for the vast majority of clients seen on the > + Internet.</p> > + > + <p>The new improvement in this patch moves all necessary > + information into the ISN again removing the need for timestamps. s/again removing/again, removing/ > + Both the MSS and send WSCALE are stored in 3 bit indexed form > + together with a single bit for SACK. While we cannot represent > + all possible MSS and WSCALE values, both are 16 bit fields in > + the TCP header, in only 3 bits each this, it turns out, is not > + actually necessary.</p> That last sentence is very unclear. I *think* it means "While we cannot represent all possible MSS and WSCALE values in only 3 bits each (both are 16 bit fields in the TCP header), it turns out that is not actually necessary.</p>" > + <p>These improvements allow one to run with SYN cookies only on > + Internet-facing servers. However while SYN cookies are > + calculated and sent all the time, they are only used when the > + syn cache overflows due to attacks or overload. In that cause s/cause/case/ > + though, you can rest assured that no significant degradation in > + TCP connection setup happens anymore and that even Windows s/anymore/any more/ > + clients can make use of window scaling and SACK.</p> > + </body> > + > + <help> > + <task>Additional testing on busy servers.</task> > + </help> > + </project> > </report> > Phew, almost done. Sorry, and thanks!
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