Re: Obscure zsh history overflow with segfault

[Peter Stephenson <p.w.stephenson@ntlworld.com>]

On Tue, 24 Jan 2012 12:28:19 -0800
Bart Schaefer <schaefer@brasslantern.com> wrote:

> On Jan 21,  4:39am, Daniel Shahaf wrote:
> }
> } Apparently, 'r 100 foo' should re-execute the portion of your history
> } from event #100 to event 'foo'.
> } 
> } Sounds like a bad idea...
> 
> Interesting.  Here we are:
> 
> 1516                /*
> 1517                 * Nasty behaviour results if we use the current history
> 1518                 * line here.  Treat it as if it doesn't exist, unless
> 1519                 * that gives us an empty range.
> 1520                 */
> 1521                if (last >= curhist) {
> 1522                    last = curhist - 1;
> 1523                    if (first > last) {
> 1524                        unqueue_signals();
> 1525                        zwarnnam("fc",
> 1526                          "current history line would recurse endlessly, aborted");
> 1527                        fclose(out);
> 1528                        unlink(fil);
> 1529                        return 1;
> 1530                    }
> 1531                }
> 
> In the situation in this bug, first > last is true but last >= curhist
> is false.  I believe that means that even though this is an infinite
> loop, we don't detect that it will be.

I'm not really following the problem, but do you mean something like
this?

Index: Src/builtin.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/builtin.c,v
retrieving revision 1.254
diff -p -u -r1.254 builtin.c
--- Src/builtin.c	29 Aug 2011 17:21:40 -0000	1.254
+++ Src/builtin.c	26 Jan 2012 20:56:28 -0000
@@ -1652,6 +1652,12 @@ fclist(FILE *f, Options ops, zlong first
 	last = first;
 	first = tmp;
     }
+    if (first > last) {
+	zwarnnam("fc", "history events are in wrong order, aborted");
+	if (f != stdout)
+	    fclose(f);
+	return 1;
+    }
     /* suppress "no substitution" warning if no substitution is requested */
     if (!subs)
 	fclistdone = 1;

-- 
Peter Stephenson <p.w.stephenson@ntlworld.com>
Web page now at http://homepage.ntlworld.com/p.w.stephenson/