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Date: Tue, 28 Nov 2017 23:12:37 +0100
From: "Luis R. Rodriguez" <>
To: Kees Cook <>
Cc: "Luis R. Rodriguez" <>,
	Djalal Harouni <>,
	Andy Lutomirski <>,
	Andrew Morton <>,
	James Morris <>,
	Ben Hutchings <>,
	Solar Designer <>,
	Serge Hallyn <>, Jessica Yu <>,
	Rusty Russell <>,
	LKML <>,
	linux-security-module <>,,
	Jonathan Corbet <>, Ingo Molnar <>,
	"David S. Miller" <>,
	Network Development <>,
	Peter Zijlstra <>,
	Linus Torvalds <>
Subject: Re: [PATCH v5 next 1/5] modules:capabilities: add

On Tue, Nov 28, 2017 at 01:39:58PM -0800, Kees Cook wrote:
> On Tue, Nov 28, 2017 at 1:16 PM, Luis R. Rodriguez <> wrote:
> > And *all* auto-loading uses aliases? What's the difference between auto-loading
> > and direct-loading?
> The difference is the process privileges. Unprivilged autoloading
> (e.g. int n_hdlc = N_HDLC; ioctl(fd,
> TIOCSETD, &n_hdlc)), triggers a privileged call to finit_module()

Ah, so system call implicated request_module() calls.

> >> We already have a global sysctl for blocking direct-loading (modules_disabled).
> >
> > My point was that even if you have a CAP_NET_ADMIN check on request_module(),
> > finit_module() will not check for it, so a crafty userspace could still try
> > to just finit_module() directly, and completely then bypass the CAP_NET_ADMIN
> > check.
> You need CAP_SYS_MODULE to run finit_module().

OK and since CAP_SYS_MODULE is much more restrictive one could argue, what's the
point here?


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