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Date: Fri, 4 Oct 2013 10:05:38 +0100
From: Djalal Harouni <>
To: Ingo Molnar <>
Cc: Kees Cook <>,
	Andy Lutomirski <>,
	"Eric W. Biederman" <>,
	Al Viro <>,
	Andrew Morton <>,
	Linus Torvalds <>,
	"Serge E. Hallyn" <>,
	Cyrill Gorcunov <>,
	David Rientjes <>,
	LKML <>,
	Linux FS Devel <>,
	"" <>,
	Djalal Harouni <>
Subject: Re: [PATCH v2 0/9] procfs: protect /proc/<pid>/* files with

On Thu, Oct 03, 2013 at 08:12:44AM +0200, Ingo Molnar wrote:
> So please first get consensus on this fundamental design question before 
> spreading your solution to more areas.
Check file_ns_capable() added in commit 935d8aabd4331 by Linus
Add file_ns_capable() helper function for open-time capability checking

commit 6708075f104c3c9b0 by Eric,
userns: Don't let unprivileged users trick privileged users into setting
the id_map

So they add file_ns_capable() to inspect file->f_cred during ->write()

The difference between the function I've added proc_allow_access() and
file_ns_capable() is that proc_allow_access() will check if it's
absolutely the same user, otherwise fallback to security_capable() which
is the heart of file_ns_capable()

So it's already been done and proposed! this is an easy solution to
detect if current's cred have changed.

> Thanks,
> 	Ingo

Djalal Harouni

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