Path: utzoo!mnetor!uunet!husc6!tut.cis.ohio-state.edu!mailrus!nrl-cmf!ames!lll-tis!elxsi!beatnix!gww
From: gww@beatnix.UUCP (Gary Winiger)
Newsgroups: comp.bugs.4bsd
Subject: Vi can longjmp before setjmp is called. +Fix
Message-ID: <726@elxsi.UUCP>
Date: 12 Mar 88 20:10:16 GMT
Sender: nobody@elxsi.UUCP
Reply-To: gww@beatnix.UUCP (Gary Winiger)
Organization: ELXSI Super Computers, San Jose
Lines: 62

Subject: Vi can longjmp before setjmp is called. +Fix
Index:	ucb/ex/ex.h 4.3BSD +Fix

Description:
	It is possible for vi to take a longjmp before the setjmp has
	completed.
Repeat-By:
	The macro CATCH (defined in ex.h) sets a flag to tell if the
	the jump buffer is valid.  At least in fastpeekkey() (ex_vget.c)
	the signal can be user generated (SIGINT).  With the original
	version of CATCH the flag is set before the setjmp is called, 
	thus with a lot of good luck, one could enter the signal handler
	(trapalarm()) before the setjmp.
	By inspection of CATCH in ex.h.
Fix:
	The attached code solves this problem at Elxsi.

Gary..
{ucbvax!sun,lll-lcc!lll-tis,amdahl!altos86,bridge2}!elxsi!gww
--------- cut --------- snip --------- :.,$w diff -------------
Index: ucb/ex/ex.h
*** /tmp/,RCSt1003323	Tue Sep 22 16:42:41 1987
--- ex.h	Tue Sep 22 16:39:02 1987
***************
*** 1,6 ****
! /*	$Header: ex.h,v 1.1 86/12/23 18:15:35 gww Exp $ ENIX BSD
   *
   * $Log:	ex.h,v $
   * Revision 1.1  86/12/23  18:15:35  gww
   * Initial revision
   * 
--- 1,10 ----
! /*	$Header: ex.h,v 1.2 87/09/22 16:37:57 gww Exp $ ENIX BSD
   *
   * $Log:	ex.h,v $
+  * Revision 1.2  87/09/22  16:37:57  gww
+  * Guard against possible timing bug.  If a signal comes before the setjmp has
+  * been executed.  (This version of the fix by corbett.)
+  * 
   * Revision 1.1  86/12/23  18:15:35  gww
   * Initial revision
   * 
***************
*** 259,266 ****
  #define	setlastchar(c)	lastc = c
  #define	ungetchar(c)	peekc = c
  
! #define	CATCH		vcatch = 1; if (setjmp(vreslab) == 0) {
! #define	ONERR		} else { vcatch = 0;
  #define	ENDCATCH	} vcatch = 0;
  
  /*
--- 263,270 ----
  #define	setlastchar(c)	lastc = c
  #define	ungetchar(c)	peekc = c
  
! #define	CATCH		if (vcatch = !setjmp(vreslab)) {
! #define	ONERR		} else {
  #define	ENDCATCH	} vcatch = 0;
  
  /*