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Date: Mon, 4 Feb 2002 13:58:51 -0800 (PST)
From: Joseph Ishac <jishac@grc.nasa.gov>
To: freebsd-gnats-submit@FreeBSD.org
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Subject: kern/34619: TCP - FINs with different sequence numbers
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>Number:         34619
>Category:       kern
>Synopsis:       TCP - FINs with different sequence numbers
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Feb 04 14:00:02 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     Joseph Ishac
>Release:        
>Organization:
NASA Glenn Research Center
>Environment:
>Description:
      Problem (below) discovered on OpenBSD. The problem code exists in the current (1.39.2.14) version of src/sys/netinet/tcp_output.c. However, the problem has not been verified on a FreeBSD box.  OpenBSD fix by Niels Provos.

After loosing a packet in the final window of data, the resulting retransmission carries the FIN bit erroneously (it is not the final packet and carries a different sequence number).

See: OpenBSD PR number 2368 (http://cvs.openbsd.org/cgi-bin/wwwgnats.pl/full/2368) for sample output.
>How-To-Repeat:
      
>Fix:
      OpenBSD solution from Niels Provos <provos@citi.umich.edu>

 Index: tcp_output.c
 ===================================================================
 --- tcp_output.c	14 Jan 2002 19:58:18 -0000	1.46
 +++ tcp_output.c	2 Feb 2002 01:01:37 -0000
  		len = tp->t_maxseg;
  		sendalot = 1;
  	}
 -	if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
 +	if (off + len < so->so_snd.sb_cc)
  		flags &= ~TH_FIN;
  
  	win = sbspace(&so->so_rcv);
 
>Release-Note:
>Audit-Trail:
>Unformatted:

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