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

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Message-ID: <202401240958.8D9A11E8E@keescook>
Date: Wed, 24 Jan 2024 10:57:38 -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>,
	Kentaro Takeda <takedakn@...data.co.jp>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	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've tested AppArmor, and this works fine:

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 7717354ce095..ab104ce05f96 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -470,7 +470,7 @@ static int apparmor_file_open(struct file *file)
 	 * implicit read and executable mmap which are required to
 	 * actually execute the image.
 	 */
-	if (current->in_execve) {
+	if (file->f_flags & __FMODE_EXEC) {
 		fctx->allow = MAY_EXEC | MAY_READ | AA_EXEC_MMAP;
 		return 0;
 	}

Converting TOMOYO is less obvious to me, though, as it has a helper that
isn't strictly always called during open(). I haven't finished figuring
out the call graphs for it...

-- 
Kees Cook