Re: [tcpm] ECN++ control packet handling
Bob Briscoe <ietf@bobbriscoe.net> Tue, 09 February 2021 15:48 UTC
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To: "Scheffenegger, Richard" <rs.ietf@gmx.at>
References: <d5754c0e-f45b-9cf0-1a68-e90eee0740c7@gmx.at>
From: Bob Briscoe <ietf@bobbriscoe.net>
Cc: "tcpm@ietf.org" <tcpm@ietf.org>, draft-ietf-tcpm-generalized-ecn@ietf.org
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Date: Tue, 09 Feb 2021 15:48:52 +0000
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Subject: Re: [tcpm] ECN++ control packet handling
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Richard, Good point. Thanks for noticing this potential implementation pit-fall. In my local copy of the ECN++ draft I have added the following to the end of "3.2.6 RST (Send)": + Implementers SHOULD ensure that RST packets (and control packets + generally) are always sent out with the same ECN field regardless of + the TCP state machine. Otherwise the ECN field could reveal internal + TCP state. For instance, the ECN field on a RST ought not to reveal + any distinction between a non-listening port, a recently in-use + port, and a closed session port. And I've added this to the end of Security Considerations: + Section 3.2.6 on sending TCP RSTs points out + that implementers need to take care to ensure that the ECN field on a + RST does not depend on TCP's state machine. Otherwise the internal + information revealed could be of use to potential attackers. This point + applies more generally to all control packets, not just RSTs. Do you think that's correct / sufficient? Cheers Bob On 08/02/2021 21:03, Scheffenegger, Richard wrote: > Hi Bob, Marcelo, > > While working on the ecn++ code for fbsd patch, I found that the > codepath for dealing with out-of-window, past-established and > non-listening ports is actually quite different there. > > Casually glancing over the draft for ecn++, I didn’t find a reference > specifically about the handling of RST (non-listening port, vs. closing > session etc). > > This may need a hint in the security section, that an implementation > should ensure, that control packets are always sent out with similar > headers, regardless of the TCP state machine. Otherwise, you could > potentially leak information (eg. Recently in-use ports) which may be a > clue to malicious players… > > > Richard Scheffenegger > > _______________________________________________ > tcpm mailing list > tcpm@ietf.org > https://www.ietf.org/mailman/listinfo/tcpm -- ________________________________________________________________ Bob Briscoe http://bobbriscoe.net/
- [tcpm] ECN++ control packet handling Scheffenegger, Richard
- Re: [tcpm] ECN++ control packet handling Bob Briscoe
- Re: [tcpm] ECN++ control packet handling Scheffenegger, Richard