linux-hardening - Re: [PATCH] exec: Check __FMODE_EXEC instead of in

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Date: Thu, 25 Jan 2024 15:59:18 +0100
From: Jann Horn <jannh@...gle.com>
To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc: Kees Cook <keescook@...omium.org>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Josh Triplett <josh@...htriplett.org>, Kevin Locke <kevin@...inlocke.name>, 
	John Johansen <john.johansen@...onical.com>, Paul Moore <paul@...l-moore.com>, 
	James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, 
	Kentaro Takeda <takedakn@...data.co.jp>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	Eric Biederman <ebiederm@...ssion.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
	apparmor@...ts.ubuntu.com, linux-security-module@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] exec: Check __FMODE_EXEC instead of in_execve for LSMs

On Thu, Jan 25, 2024 at 3:35 PM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> On 2024/01/25 6:50, Kees Cook wrote:
> > Yeah, I was just noticing this. I was over thinking. :) It does look
> > like all that is needed is to remove __FMODE_EXEC.
>
> I worry that some out-of-tree kernel code continues using __FMODE_EXEC for
> opening for non-execve() purpose. If that happened, TOMOYO will be fooled...

I just scrolled through the Github code search results for the query
"__FMODE_EXEC -path:fs/exec.c -path:fs/fcntl.c -path:fs/nfs/
-path:security/tomoyo/ -path:security/apparmor/
-path:include/linux/fsnotify.h -path:nfs/dir.c
-path:include/linux/fs.h -path:security/landlock/", and the only place
I saw in there that sets __FMODE_EXEC, other than copies of core
kernel code in weirdly named files, was this one hit in a patch for
the 2.6.39 kernel to add plan9 syscalls:

https://github.com/longlene/clx/blob/fdf996e0c2a7835d61ee827a82146723de76a364/sys-kernel/glendix-sources/files/glendix_2.6.39.patch#L2833

Debian codesearch also doesn't show anything relevant.

So I don't think we have to be particularly worried about that.