louie@umd5 (Louis Mamakos) (08/27/86)
Subject: sending data after a FIN
Index: sys/netinet/tcp_output.c 4.3BSD
Description:
tcp_output.c will emit a segment with a FIN even if it cannot send
all of the remaining data in the socket. Consider a host which
offers a 1000 byte window, but whose maximum segment size is 576
bytes. Take the case where the user has sent some data on a
connection, and close()ed the socket. If there is between 576
and 1000 bytes remaining, it will attempt to send it all. It will
not clear the FIN since it fits within the offered window, but
will only send the max segment size number of bytes. Later, it
will emit a subsequent segment with a FIN, carrying a different
sequence number.
Repeat-By:
Difficult to reproduce; try to FTP to such a host.
Fix:
Add check of tp->t_maxseg when clearing the FIN bit in the
segment to be sent.
RCS file: RCS/tcp_output.c,v
retrieving revision 1.1
retrieving revision 1.2
diff -c -r1.1 -r1.2
*** /tmp/,RCSt1000310 Tue Aug 26 19:19:54 1986
--- /tmp/,RCSt2000310 Tue Aug 26 19:19:56 1986
***************
*** 91,97 ****
len = MIN(so->so_snd.sb_cc, win) - off;
flags = tcp_outflags[tp->t_state];
! if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
flags &= ~TH_FIN;
if (len < 0) {
--- 92,99 ----
len = MIN(so->so_snd.sb_cc, win) - off;
flags = tcp_outflags[tp->t_state];
! if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc) ||
! (len > tp->t_maxseg)) /* what we're REALLY going to send */
flags &= ~TH_FIN;
if (len < 0) {
Share and enjoy.
-----------------------------------------------------------------------------
Louis A. Mamakos WA3YMH Internet: louie@TRANTOR.UMD.EDU
University of Maryland, Computer Science Center - Systems Programming
--
Louis A. Mamakos WA3YMH University of Maryland, Computer Science Center
Internet: louie@trantor.umd.edu
UUCP: {seismo!umcp-cs, ihnp4!rlgvax}!cvl!umd5!louie