linux-kernel - Re: [6.8-rc1 Regression] Unable to exec apparmor

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Date: Wed, 24 Jan 2024 09:21:14 -0800
From: Kees Cook <keescook@...omium.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kevin Locke <kevin@...inlocke.name>,
	John Johansen <john.johansen@...onical.com>,
	Josh Triplett <josh@...htriplett.org>,
	Mateusz Guzik <mjguzik@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [6.8-rc1 Regression] Unable to exec apparmor_parser from
 virt-aa-helper

On Wed, Jan 24, 2024 at 09:10:58AM -0800, Linus Torvalds wrote:
> On Wed, 24 Jan 2024 at 08:54, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > Hmm. That whole thing is disgusting. I think it should have checked
> > FMODE_EXEC, and I have no idea why it doesn't.
> 
> Maybe because FMODE_EXEC gets set for uselib() calls too? I dunno. I
> think it would be even better if we had the 'intent' flags from
> 'struct open_flags' available, but they aren't there in the
> file_open() security chain.

I think there were other problems that I might have already fixed when I
reorganized things in commit 0fd338b2d2cd ("exec: move path_noexec() check
earlier") to more correctly map to LSM checks.

> Anyway, moving current->in_execve earlier looks fairly trivial, but I
> worry about the randomness. I'd be *so*( much happier if this crazy
> flag went away, and it got changed to look at the open intent instead.
> 
> Attached patch is ENTIRELY UNTESTED. And disgusting.

I opted to tie "current->in_execve" lifetime to bprm lifetime just to
have a clean boundary (i.e. strictly in alloc/free_bprm()).

-Kees

-- 
Kees Cook