[6.8-rc1 Regression] Unable to exec apparmor_parser from virt-aa-helper

[Linus Torvalds]

On Wed, 24 Jan 2024 at 09:27, Linus Torvalds
<torvalds at linux-foundation.org> wrote:
>
> IOW, I think the goal here should be "minimal fix" followed by "remove
> that horrendous thing".

Ugh. The tomoyo use is even *more* disgusting, in how it uses it for
"tomoyo_domain()" entirely independently of even the ->file_open()
callback.

So for tomoyo, it's not about the file open, it's about
tomoyo_cred_prepare() and friends.

So the patch I posted probably fixes apparmor, but only breaks tomoyo
instead, because tomoyo really does seem to use it around the whole
security_bprm_creds_for_exec() thing.

Now, tomoyo *also* uses it for the file_open() callback, just to confuse things.

IOW, I think the right thing to do is to split this in two:

 - leave the existing ->in_execve for the bprm_creds dance in
boprm_execve(). Horrendous and disgusing.

 - the ->file_open() thing is changed to check file->f_flags

(with a comment about how FMODE_EXEC is in f_flags, not f_mode like it
should be).

IOW, I think the patch I posted earlier - and Kees' version of the
same thing - is just broken. This attached patch might work.

And as noted, since it checks __FMODE_EXEC, it now allows the uselib()
case too. I think that's ok.

UNTESTED. But I think this is at least a movement in the right
direction. The whole cred use of current->in_execve in tomoyo should
*also* be fixed, but I didn't even try to follow what it actually
wanted.

           Linus