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Subject: [Bug 213232] [tcp] [panic] tcp_output() Panic String: tcp_output:
 len > IP_MAXPACKET on -head and stable/11
Date: Sun, 16 Oct 2016 06:16:51 +0000
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D213232

Hiren Panchasara <hiren@FreeBSD.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |glebius@FreeBSD.org

--- Comment #6 from Hiren Panchasara <hiren@FreeBSD.org> ---
Now with r306769, len is int32_t so it can actually have -ve value, I am se=
eing
panic at


        /*
         * This KASSERT is here to catch edge cases at a well defined place.
         * Before, those had triggered (random) panic conditions further do=
wn.
         */
        KASSERT(len >=3D 0, ("[%s:%d]: len < 0", __func__, __LINE__));

Now, putting a bit of debugs above that I figured that at following path in
'else' case the len becomes -ve

                if (tso) {

                   <blah>

                } else {
                        len =3D tp->t_maxseg - optlen - ipoptlen;
                        sendalot =3D 1;
                }

I found that tp-t_maxseg =3D 2, optlen =3D 12, ipoptlen =3D 0 resulting in =
len =3D -10.

Clearly, t_maxseg which is supposed to be representing MSS at '2' looks wro=
ng.

I wonder if the changes in
https://svnweb.freebsd.org/base?view=3Drevision&revision=3D293284 somewhere=
 caused
this.

Still investigating.

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