misc/177456: An error of calculating TCP sequence number will resault in the machine to restart

[Gleb Smirnoff]

The following reply was made to PR kern/177456; it has been noted by GNATS.

From: Gleb Smirnoff <glebius at FreeBSD.org>
To: ?????? <lglion718 at 163.com>
Cc: bug-followup at FreeBSD.org
Subject: Re: misc/177456: An error of calculating TCP sequence number will
 resault in the machine to restart
Date: Wed, 3 Apr 2013 19:21:12 +0400

   Hi!
 
 On Wed, Apr 03, 2013 at 07:52:42AM +0800, ?????? wrote:
 ?> I mean there is a bug in FreeBSD's tcp code.  I'm trying to describe it by pictuer. Pelease see the attachments??
 
 I am trying to model what you are describing in the picture by
 special crafted code.
 
 I intentionally model memory allocation failure on first two
 packets for a connection that has special socket option.
 
 I'm modelling allocation failure at tcp_output.c near line 900:
 
 Index: tcp_output.c
 ===================================================================
 --- tcp_output.c        (revision 249051)
 +++ tcp_output.c        (working copy)
 @@ -898,6 +898,13 @@ send:
                 else
                         TCPSTAT_INC(tcps_sndwinup);
  
 +               /* Fail allocating first 2 packets. */
 +               if (tp->t_flags & TF_ZHOPA && tp->t_zhopa < 2) {
 +                       tp->t_zhopa++;
 +                       m = NULL;
 +                       error = ENOBUFS;
 +                       goto out;
 +               } else
                 m = m_gethdr(M_NOWAIT, MT_DATA);
                 if (m == NULL) {
                         error = ENOBUFS;
 
 
 I have no success in reproducing your problems. With above code,
 first 2 packets are failing to allocate, but third retransmission
 succeeds and connection is established with no problems.
 
 May be I incorrectly understand your description :( Please don't
 give up and try to explain again.
 
 A modelling code that demonstrates problem would be appreciated.
 
 -- 
 Totus tuus, Glebius.