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

[John W. O'Brien]

On 9/23/18 17:50, Don Lewis wrote:
> On 23 Sep, John W. O'Brien wrote:
>> 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
>>
> 
> It looks to me like r337776 is a further performance improvement, only
> present in head, which also introduced a new bug that was fixed by
> r338406. I don't know why r338406 was merged to stable/11 since r337776
> was not.  Stable/11 only has the original fix (r337787 in head, r337803
> in stable/11).

Hi Don,

I'm looking at this line of code [5] in releng/11.2. It looks to me like
that's what r338406 fixed in head [6]. Am I being obtuse here?

[5]
https://svnweb.freebsd.org/base/releng/11.2/sys/netinet6/frag6.c?annotate=337828#l219
[6]
https://svnweb.freebsd.org/base/head/sys/netinet6/frag6.c?r1=338406&r2=338405&pathrev=338406

-- 
John W. O'Brien
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    0x33C4D64B895DBF3B

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