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Date: Mon, 15 May 2017 19:23:26 +0000
From: Alexey Dokuchaev <danfe@FreeBSD.org>
To: Nikolai Lifanov <lifanov@FreeBSD.org>
Cc: Konstantin Belousov <kib@FreeBSD.org>, svn-src-head@freebsd.org,
 svn-src-all@freebsd.org, src-committers@freebsd.org
Subject: Re: svn commit: r318313 - head/libexec/rtld-elf
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On Mon, May 15, 2017 at 03:09:33PM -0400, Nikolai Lifanov wrote:
> On 05/15/2017 14:52, Alexey Dokuchaev wrote:
> > Does it mean that old Linux' trick of /lib/ld-linux.so.2 /bin/chmod +x
> > /bin/chmod would now be possible on FreeBSD as well?  Does this have
> > any security implications?
> 
> This is a use case for fixing accidentally hosed /bin/chmod binary and
> not some sort of an escalation thing. You will need to be root to do
> this.

Because /bin/chmod is owned by root, not because /libexec/ld-elf.so.1 is
limiting execution to root only, or is it (I might have missed uid check
in that patch [1], but at a quick glance I didn't see it).

On a living system, there are plenty of other ways to restore missing
+x on /bin/chmod as long as you can call chmod(2), from simple Python
script down to manually crafting small binary in hex.

> Likewise, with working chmod binary, you should be able to mark
> binaries with write access executable.

Well, it's not just about chmod(1), this opens what can be a can of worms
and I want to know how big it is.

./danfe

[1] Idea for security.bsd.ld_elf_exec_root_only sysctl(8)?