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Date: Tue, 28 Nov 2017 13:39:58 -0800
From: Kees Cook <>
To: "Luis R. Rodriguez" <>
Cc: 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 request_module_cap()

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()

>> 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().


Kees Cook
Pixel Security

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