Re: [screen-devel] Memory Leak in FreeAltScreen

[Bill Pursell]

Juergen Weigert wrote:
> On Mar 27, 06 05:41:04 +0100, Bill Pursell wrote:
>
> > Daniel De Graaf wrote:
> >
> > > In FreeAltScreen, the w_alt_mlines and w_alt_hlines entries are not
> > > freed before setting them to zero. This causes a memory leak every
> > > time a screen is switched, which can be demonstrated by the shell
> > > script "for a in `seq 1 1000`; do echo test|less -E;done".
> > >
> > > - Daniel De Graaf
> > >
> > > --- resize.c.orig       2003-09-08 09:26:31.000000000 -0500
> > > +++ resize.c    2006-03-26 13:16:26.000000000 -0600
> > > @@ -1045,8 +1045,10 @@
> > >
> > >  if (p->w_alt_mlines)
> > >    for (i = 0; i < p->w_alt_height; i++)
> > >      FreeMline(p->w_alt_mlines + i);
> > > +  free(p->w_alt_mlines);
> > > +  free(p->w_alt_hlines);
> > >  p->w_alt_mlines = 0;
> > >  p->w_alt_width = 0;
> > >  p->w_alt_height = 0;
> > >  p->w_alt_x = 0;
> >
> > Freeing a memory address and then assigning to it is a bad idea.  Simply 
> > freeing it is adequate.
>
>
> why bad idea? I prefer to die in the NULL-Pointer access, 
> than go amok in memory that I do no longer own.
>
>         cheers,

My bad.  I mis-read the code as:

free(p->w_alt_mlines);
*p->w_alt_mlines = 0;

Which is definitely a bad idea :)