[Bug 225536] ipfw tcp-setmss doesn't seems to work

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225536

Rodney W. Grimes  changed:

   What|Removed |Added

 CC||i...@freebsd.org

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[Bug 225536] ipfw tcp-setmss doesn't seems to work

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225536

Andrey V. Elsukov  changed:

   What|Removed |Added

 Resolution|--- |FIXED
 Status|New |Closed
   Assignee|i...@freebsd.org|a...@freebsd.org

--- Comment #11 from Andrey V. Elsukov  ---
Fixed in head/ and stable/11. Thanks!

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[Bug 225536] ipfw tcp-setmss doesn't seems to work

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225536

--- Comment #10 from commit-h...@freebsd.org ---
A commit references this bug:

Author: ae
Date: Thu Aug 16 09:42:09 UTC 2018
New revision: 337902
URL: https://svnweb.freebsd.org/changeset/base/337902

Log:
  MFC r337469:
Use host byte order when comparing mss values.

This fixes tcp-setmss action on little endian machines.

PR: 225536
Submitted by:   John Zielinski

Changes:
_U  stable/11/
  stable/11/sys/netpfil/ipfw/pmod/tcpmod.c

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[Bug 225536] ipfw tcp-setmss doesn't seems to work

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225536

--- Comment #9 from commit-h...@freebsd.org ---
A commit references this bug:

Author: ae
Date: Wed Aug  8 17:32:03 UTC 2018
New revision: 337469
URL: https://svnweb.freebsd.org/changeset/base/337469

Log:
  Use host byte order when comparing mss values.

  This fixes tcp-setmss action on little endian machines.

  PR:   225536
  Submitted by: John Zielinski

Changes:
  head/sys/netpfil/ipfw/pmod/tcpmod.c

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[Bug 225536] ipfw tcp-setmss doesn't seems to work

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225536

--- Comment #8 from John Zielinski  ---
The incorrect network order byte compare on a little endian processor explains
exactly what Emmanuel is seeing.

An mss of 8960 (0x0023 network order) which is compared <= to the desired mss
of 1460 (0xB405 network order) will be true and break out before setting the
mss.  The test value of 1400 (0x7805 network order) will also break out.

In the case where the locally generated traffic worked with the 1400 rule I
suspect the mss was 1460 already.  So 1460 (0xB405 network order) <= 1400
(0x7805 network order) is false, since we're comparing the network order
values, we don't break and go on to set the mss in the packet.

People using it for the usual PPPoE clamp would normally not notice on normal
1460  mss packets.  The 1460 (0xB405 network order) <= 1452 (0xAC05 network
order) test would be false and the mss would be changed.  Any device using an
mss less than 1460 might have its mss increased.

This bug also affects me as I also use MTU 9000 (mss 8960) on my internal
network.  After I applied my patch and reloaded the kernel module it started
working and setting the mss properly.

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[Bug 225536] ipfw tcp-setmss doesn't seems to work

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225536

John Zielinski  changed:

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 CC||aver...@gmail.com

--- Comment #7 from John Zielinski  ---
Created attachment 195605
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=195605=edit
Fix for little endian machines

The tcp-setmss option is broken on little endian machines.  The comparison
between oldmss and mss needs to be done in host byte order.

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[Bug 225536] ipfw tcp-setmss doesn't seems to work

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gra...@menhennitt.com.au changed:

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--- Comment #6 from gra...@menhennitt.com.au ---
(In reply to Emmanuel Vadot from comment #5)

Emmanuel,


I can't tell you why it matters, but I can say that it does make a significant
difference.

See my mailing list thread about this from last year at
https://lists.freebsd.org/pipermail/freebsd-ipfw/2017-August/006578.html
(disabling TSO). Slightly related is another thread
https://lists.freebsd.org/pipermail/freebsd-ipfw/2017-September/006585.html
(disable TXCSUM).

Also, see the ipfw(8) man page in the BUGS section:

"Due to the architecture of libalias(3), ipfw nat is not compatible with the
TCP segmentation offloading (TSO).  Thus, to reliably nat network traffic,
please disable TSO on your NICs using ifconfig(8)."

Graham

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[Bug 225536] ipfw tcp-setmss doesn't seems to work

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--- Comment #5 from Emmanuel Vadot  ---
(In reply to Emmanuel Vadot from comment #4)

What is the reason for disabling TSO when using NAT btw ?

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[Bug 225536] ipfw tcp-setmss doesn't seems to work

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225536

--- Comment #4 from Emmanuel Vadot  ---
(In reply to Andrey V. Elsukov from comment #3)

 Yes exactly.

I didn't know about disabling TSO when using NAT, I'll test that tomorrow.
Thanks.

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[Bug 225536] ipfw tcp-setmss doesn't seems to work

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225536

Andrey V. Elsukov  changed:

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--- Comment #3 from Andrey V. Elsukov  ---
(In reply to Emmanuel Vadot from comment #2)
> I've just tested without NAT (just bypassing by adding the destination IP on
> a discarded table) and the situation is the same.
> So maybe fib are the problems ?

Can you clarify a bit, is tcp-setmss works for locally originated traffic, and
doesn't work for forwarded traffic not depending from presence of NAT?

Also, since you use NAT, you need to disable TSO on the used NICs.

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[Bug 225536] ipfw tcp-setmss doesn't seems to work

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Mark Linimon  changed:

   What|Removed |Added

   Assignee|freebsd-b...@freebsd.org|freebsd-ipfw@FreeBSD.org

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