Re: Segmentation fault due to double free for archetype.

[Takashi Yano <takashi.yano@nifty.ne.jp>]

On Mon, 17 Jan 2022 12:01:51 +0100
Corinna Vinschen wrote:
> On Jan 15 19:20, Takashi Yano wrote:
> > I also found the following patch fixes the issue. Is this the
> > right thing?
> > 
> > diff --git a/winsup/cygwin/fhandler.cc b/winsup/cygwin/fhandler.cc
> > index fc7c0422e..e51208117 100644
> > --- a/winsup/cygwin/fhandler.cc
> > +++ b/winsup/cygwin/fhandler.cc
> > @@ -441,7 +441,7 @@ fhandler_base::open_with_arch (int flags, mode_t mode)
> >  	|| open (flags, mode & 07777)))
> >      {
> >        if (archetype)
> > -	delete archetype;
> > +	cygheap->fdtab.delete_archetype (archetype);
> >      }
> >    else if (archetype)
> >      {
> 
> Good catch!  I think this is basically ok, but you have to check the
> usecount, i. e.
> 
>   if (archetype && archetype_usecount (-1) == 0)
>     cygheap->fdtab.delete_archetype (archetype);
> 
> Does that sound right?

Where is archetype->usecount is incremented? It seems that
archetype->usecount is zero here. archetype->usecount is not
incremented around line 672 in dtable.cc when archetype is
created by fh->clone().

  else
    {
      if (!fh->get_name ())
        fh->set_name (fh->dev ().native ());
      fh->archetype = fh->clone ();
      debug_printf ("created an archetype (%p) for %s(%d/%d)", fh->archetype, fh->get_name (), fh->dev ().get_major (), fh->dev ().get_minor ());
      fh->archetype->archetype = NULL;
      *cygheap->fdtab.add_archetype () = fh->archetype;
    }

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>