linux-kernel - Re: Kernel panic at Ubuntu: IMA + Apparmor

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Message-ID: <20140425212128.GB18016@ZenIV.linux.org.uk>
Date:	Fri, 25 Apr 2014 22:21:28 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Dmitry Kasatkin <d.kasatkin@...sung.com>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	John Johansen <john.johansen@...onical.com>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	James Morris <jmorris@...ei.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kernel-team <kernel-team@...ts.ubuntu.com>
Subject: Re: Kernel panic at Ubuntu: IMA + Apparmor

On Fri, Apr 25, 2014 at 01:45:17PM -0700, Eric W. Biederman wrote:

> IMA-appraisal is fundamentally broken because I can take a mandatory
> file lock and prevent IMA-apprasial.
> 
> Using kernel_read is what allows this.
> 
> > Isn't it a clear motivating case???
> 
> kernel_read is not appropriate for IMA use.  The rest of this is just
> the messenger.
> 
> IMA needs to use a cousin of kernel_read that operates at a lower level
> than vfs_read.  A function that all of the permission checks and the
> fsnotify work.

It's worse than that, actually ;-/  IMA hooks in __fput() have interesting
interplay with revoke-related stuff as well.  Another very messy thing in
the same area is that it actually does ->read() from under ->i_mutex, leading
to all kinds of interesting locking issues...

I doubt that your "let's open-code vfs_read() guts" would be a good idea;
if nothing else, it might make more sense to make rw_verify_area() skip
the mandlock and security theatre when called in such situation.

What a mess... ;-/
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