linux-kernel - Re: [kernel-hardening] [PATCH v1 1/1] Add Trusted Path Execution as a stackable LSM

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Message-ID: <CAG48ez1W6Pwxuhc92OGvtmLQLE8XhXCJvZDoqDCMSODvtGUT_A@mail.gmail.com>
Date:   Sat, 3 Jun 2017 12:39:03 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Matt Brown <matt@...tt.com>
Cc:     james.l.morris@...cle.com, serge@...lyn.com,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [kernel-hardening] [PATCH v1 1/1] Add Trusted Path Execution as a
 stackable LSM

On Sat, Jun 3, 2017 at 7:53 AM, Matt Brown <matt@...tt.com> wrote:
> This patch was modified from Brad Spengler's Trusted Path Execution (TPE)
> feature in Grsecurity and also incorporates logging ideas from
> cormander's tpe-lkm.
>
> Modifications from the Grsecurity implementation of TPE were made to
> turn it into a stackable LSM using the existing LSM hook bprm_set_creds.
> Also, denial messages were improved by including the full path of the
> disallowed program. (This idea was taken from cormander's tpe-lkm)
[...]
> Threat Models:
[...]
> 2. Attacker on system replaces binary used by a privileged user with a
>    malicious one
>
> *  This situation arises when administrator of a system leaves a binary
>    as world writable.
>
> *  TPE is very effective against this threat model

How do you end up with world-writable binaries in $PATH?