IPv6 fragment reassembly regression following FreeBSD-SA-18:10.ip

John W. O'Brien john at saltant.com
Sun Sep 23 13:43:39 UTC 2018

I'd like to check my understanding and then ask a procedural question.

FreeBSD-SA-18:10.ip [0], released on 08/14, was resolved by r337828 [1].
That changeset, resulting in 11.1R-p13 and 11.2R-p2, included a patch to
the way IPv6 fragment reassembly is handled [2] that was part of the
merge to releng. In an ensuing thread [3] two weeks later, an
implementation defect was identified, but not before that defect had
shipped. The defect is now being tracked as a bug [4], as of 09/03 has
been fixed in head and stable/11, and is registered as a blocker for 12.0.

I believe this defect is the cause of a problem I detected recently
where postfix would query BIND on ::1 for the DNSSEC-signed AAAA of an
MX, and never receive a response. I'm a little puzzled that lo0 is
affected in spite of having a 16k MTU, but the other signs are there:
the symptoms appeared after upgrading from 11.2R-p1 to -p3, and I can
perform that query successfully on UDPv4 or TCPv6.

What I have been unable so far to determine is, will another 11.2R patch
be forthcoming to resolve this regression, and if so, when? I can limp
along without UDPv6 for a little while, but not until 11.3. The only
clear alternative is to downgrade to -p1.

[0] https://www.freebsd.org/security/advisories/FreeBSD-SA-18:10.ip.asc
[1] https://svnweb.freebsd.org/changeset/base/337828
[2] https://svnweb.freebsd.org/changeset/base/337776
[3] https://lists.freebsd.org/pipermail/svn-src-head/2018-August/117514.html
[4] https://bugs.freebsd.org/231045

John W. O'Brien
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