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From Steve Hay <steve.m....@googlemail.com.INVALID>
Subject Re: Fix for Segfault with Apache and mod_perl
Date Fri, 21 Jun 2019 07:38:34 GMT
Thanks for the report, Sam (and to Joe for the fix). This is now
committed to mod_perl trunk:
http://svn.apache.org/viewvc?view=revision&revision=1861755

On Thu, 20 Jun 2019 at 09:07, Steve Hay <steve.m.hay@googlemail.com> wrote:
>
> Looks fine to me too. Will give it a test...
>
> On Thu, 20 Jun 2019 at 01:28, Philippe Chiasson <gozer@ectoplasm.org> wrote:
> >
> > Looks good to me
> >
> > Sent from the depths of my mind on an iPhone
> >
> > > On Jun 19, 2019, at 17:22, Sam Vaughan <samjvaughan@gmail.com> wrote:
> > >
> > > Hi mod_perl team,
> > >
> > > I reported a bug yesterday to the Apache team, describing a segfault that only
happens if mod_perl is installed:
> > >
> > > https://bz.apache.org/bugzilla/show_bug.cgi?id=63516
> > >
> > > My impression was that it should be fixed in httpd2, but mod_perl is the only
module that adds a configuration flag to the global ap_server_config_defines array, so it
has been suggested that a one-line change go into the modperl_register_hooks() function instead:
> > >
> > > Index: src/modules/perl/mod_perl.c
> > > --- src/modules/perl/mod_perl.c.orig
> > > +++ src/modules/perl/mod_perl.c
> > > @@ -861,7 +861,7 @@
> > >
> > >     /* for <IfDefine MODPERL2> and Apache2->define("MODPERL2") */
> > >     *(char **)apr_array_push(ap_server_config_defines) =
> > > -        apr_pstrdup(p, "MODPERL2");
> > > +        apr_pstrdup(ap_server_config_defines->pool, "MODPERL2");
> > >
> > >     ap_hook_pre_config(modperl_hook_pre_config,
> > >                        NULL, NULL, APR_HOOK_MIDDLE);
> > >
> > > Essentially, the pool provided as an argument to this function doesn't have
a long enough lifetime to safely be used as backing storage for the "MODPERL2" string.  This
change uses the pool that the ap_server_config_defines array itself was created in, thereby
giving the "MODPERL2" string the same lifetime as the array it is being added to.
> > >
> > > As far as I can tell, this use-after-free bug has been sitting there for quite
a few years now but Apache only segfaults if your OS is strict enough about reclaiming/unmapping
freed memory.
> > >
> > > Currently, this issue causes httpd2 to segfault during startup the majority
of the time on OpenBSD 6.5.
> > >
> > > I'd really appreciate it if someone could either confirm that the above patch
is OK and apply it to mod_perl, or jump on the above Apache bug report and add a comment explaining
why it isn't.
> > >
> > > Thanks!
> > >
> > > Sam
> > >
> > >
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> > >
> >
> >
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> >

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