Date: Fri, 23 Feb 2001 13:34:10 -0600 From: Jonathan Lemon <jlemon@flugsvamp.com> To: Kris Kennaway <kris@obsecurity.org> Cc: arch@FreeBSD.ORG, Marcel Moolenaar <marcel@cup.hp.com> Subject: Re: sysctl kern.fallback_elf_brand Message-ID: <20010223133410.O5714@prism.flugsvamp.com> In-Reply-To: <20010223113155.B73221@mollari.cthul.hu> References: <3A960EF8.75C3FC53@cup.hp.com> <20010223042641.B2539@dragon.nuxi.com> <20010223113155.B73221@mollari.cthul.hu>
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On Fri, Feb 23, 2001 at 11:31:56AM -0800, Kris Kennaway wrote:
> On Fri, Feb 23, 2001 at 04:26:41AM -0800, David O'Brien wrote:
> > On Thu, Feb 22, 2001 at 11:19:20PM -0800, Marcel Moolenaar wrote:
> > > One problem with this is that unbranded static Linux binaries are
> > > executed as FreeBSD native binaries and there's a high chance of them
> > > rebooting the machine if run as root.
> >
> > I've never seen that. Everyone I've every tried just dumped core. Have
> > you really seen running one reboot the machine?
>
> Yes. This was under 4.2-STABLE. Unfortunately, I can't remember off
> the top of my head what the binary was - something extracted from a
> redhat 6.2 RPM, I think. Have you tried any statically linked
> binaries which make the correspondingly-numbered syscall (actually, I
> think mine triggered a halt, not a reboot, but they're both common
> syscall numbers)?
It's quite easy to reproduce. Here's why:
>From sys/kern/syscalls.master:
55 STD BSD { int reboot(int opt); }
>From sys/i386/linux/syscalls.master:
55 STD LINUX { int linux_fcntl(int fd, int cmd, int arg); }
If you run an unbranded Linux binary, our current default assumes
that it is a FreeBSD elf executable. So when the Linux binary then
calls what it thinks is fcntl, it actually winds up calling reboot.
*BEWM*
To reproduce, just compile this program (statically) on a Linux box,
and then run (as root) on a FreeBSD box:
main()
{
fcntl(0,0,0);
}
--
Jonathan
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