sendmail aborts with longjmp botch

[Chris Torek]

Index: /usr/src/usr.lib/sendmail/src/usersmtp.c 4.3BSD Fix

Description:
	When processing long mailing lists, sendmail sometimes
	aborts with a `longjmp botch'.

Repeat-by:
	Difficult.

Fix:
	The problem occurs when sendmail has a read timeout of more
	than five minutes specified in the configuration file.  In
	usersmtp.c, sendmail sets up a timeout event around the
	`greeting' reply call; this timeout is scheduled to occur in
	300 seconds (5 minutes).  It then calls reply(), which calls
	sfgets(), which notes that ReadTimeout is (e.g.) 1 hour.
	sfgets sets another timeout event for one hour, reads a line,
	clears the timeout event, and returns to usersmtp, which clears
	its own read timeout.

	Suppose, however, that no reply is made within the first five
	minutes.  Then the first event, usersmtp.c's timeout, fires
	off.  This does a longjmp() all the way out of sfgets and reply
	back to usersmtp.c, which then returns to its caller, leaving
	in the event queue the event posted by sfgets.  In one hour, if
	sendmail is still running by then, this event attempts to
	longjmp back to the context set by the sfgets from reply.  This
	context is long gone and, with any luck, longjmp notices and
	aborts.

	There are several ways to fix this.  The most general would be
	for sendmail to have a `wrapper' around setjmp and longjmp that
	would provide unwind protection.  That is beyond the scope of
	this message.

	The second way is simply to remove the 5 minute timeout from
	usersmtp.c.  Commenting out the setevent() call should
	suffice.  This is somewhat undesirable but is by far the
	easiest fix.

	The third way is to have usersmtp.c arrange for ReadTimeout to
	be set to 300, preserving its old value and restoring it after
	the first call to reply.  The following UNTESTED change does
	this.

Chris

*** usersmtp.c.old	Wed Mar  9 06:08:59 1988
--- usersmtp.c	Wed Mar  9 06:10:53 1988
***************
*** 67,72 ****
  */
  
- jmp_buf	CtxGreeting;
- 
  smtpinit(m, pvp)
  	struct mailer *m;
--- 67,70 ----
***************
*** 76,80 ****
  	EVENT *gte;
  	char buf[MAXNAME];
! 	extern greettimeout();
  
  	/*
--- 74,78 ----
  	EVENT *gte;
  	char buf[MAXNAME];
! 	int oldtimeout;
  
  	/*
***************
*** 129,138 ****
  	*/
  
! 	if (setjmp(CtxGreeting) != 0)
! 		goto tempfail;
! 	gte = setevent((time_t) 300, greettimeout, 0);
  	SmtpPhase = "greeting wait";
  	r = reply(m);
! 	clrevent(gte);
  	if (r < 0 || REPLYTYPE(r) != 2)
  		goto tempfail;
--- 127,135 ----
  	*/
  
! 	oldtimeout = ReadTimeout;
! 	ReadTimeout = 5 * 60;
  	SmtpPhase = "greeting wait";
  	r = reply(m);
! 	ReadTimeout = oldtimeout;
  	if (r < 0 || REPLYTYPE(r) != 2)
  		goto tempfail;
***************
*** 213,223 ****
  }
  
- 
- static
- greettimeout()
- {
- 	/* timeout reading the greeting message */
- 	longjmp(CtxGreeting, 1);
- }
  /*
  **  SMTPRCPT -- designate recipient.
--- 210,213 ----
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris at mimsy.umd.edu	Path:	uunet!mimsy!chris