linux-kernel - Re: [patch] remove MNT_NOEXEC check for PROT

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Message-ID: <20060927115134.GC4296@ucw.cz>
Date:	Wed, 27 Sep 2006 11:51:34 +0000
From:	Pavel Machek <pavel@....cz>
To:	David Wagner <daw-usenet@...erner.cs.berkeley.edu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [patch] remove MNT_NOEXEC check for PROT_EXEC mmaps

Hi

On Mon 25-09-06 21:36:26, David Wagner wrote:
> Pavel Machek  wrote:
> >> I'm curious about this, too.  ld-linux.so is a purely unprivileged
> >> program.  It isn't setuid root.  Can you write a variant of ld-linux.so
> >> that reads an executable into memory off of a partition mounted noexec and
> >> then begins executing that code?  (perhaps by using anonymous mmap
> >> with
> >
> >Yes, you can, but to execute your ld-linux-ignore-noexec.so variant,
> >you need to put it somewhere with exec permissions, right?
> 
> Well, yes, if you write it as a binary executable -- but not if you're
> more clever.  For instance, you can write a ld-linux-ignore-noexec.so.pl
> Perl script, store the Perl script on the noexec partition, and execute
> it via "/usr/bin/perl ld-linux-ignore-noexec.so.pl" (since I think
> Perl scripts can execute all of the system calls you'd need to use to
> write your own loader, since it's pretty well guaranteed that /usr/bin
> will live on a partition that is not marked noexec).  Note that Perl

Ok, you are right. For noexec to be effective, interpretters need to
be well-behaved, and perl is not. Maybe we should forget about
noexec, and maybe we should fix perl, I do not know.
-- 
Thanks for all the (sleeping) penguins.
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