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

[Linus Torvalds <torvalds@linux-foundation.org>]

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On Wed, 24 Jan 2024 at 09:27, Linus Torvalds
<torvalds@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

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 security/apparmor/lsm.c  | 4 +++-
 security/tomoyo/tomoyo.c | 5 +++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 7717354ce095..98e1150bee9d 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -469,8 +469,10 @@ static int apparmor_file_open(struct file *file)
 	 * Cache permissions granted by the previous exec check, with
 	 * implicit read and executable mmap which are required to
 	 * actually execute the image.
+	 *
+	 * Illogically, FMODE_EXEC is in f_flags, not f_mode.
 	 */
-	if (current->in_execve) {
+	if (file->f_flags & __FMODE_EXEC) {
 		fctx->allow = MAY_EXEC | MAY_READ | AA_EXEC_MMAP;
 		return 0;
 	}
diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index 3c3af149bf1c..e8fb02b716aa 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -327,8 +327,9 @@ static int tomoyo_file_fcntl(struct file *file, unsigned int cmd,
  */
 static int tomoyo_file_open(struct file *f)
 {
-	/* Don't check read permission here if called from execve(). */
-	if (current->in_execve)
+	/* Don't check read permission here if execve(). */
+	/* Illogically, FMODE_EXEC is in f_flags, not f_mode. */
+	if (file->f_flags & __FMODE_EXEC)
 		return 0;
 	return tomoyo_check_open_permission(tomoyo_domain(), &f->f_path,
 					    f->f_flags);