exec: Check __FMODE_EXEC instead of in_execve for LSMs

After commit 978ffcbf00 ("execve: open the executable file before
doing anything else"), current->in_execve was no longer in sync with the
open(). This broke AppArmor and TOMOYO which depend on this flag to
distinguish "open" operations from being "exec" operations.

Instead of moving around in_execve, switch to using __FMODE_EXEC, which
is where the "is this an exec?" intent is stored. Note that TOMOYO still
uses in_execve around cred handling.

Reported-by: Kevin Locke <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]
Suggested-by: Linus Torvalds <[email protected]>
Fixes: 978ffcbf00 ("execve: open the executable file before doing anything else")
Cc: Josh Triplett <[email protected]>
Cc: John Johansen <[email protected]>
Cc: Paul Moore <[email protected]>
Cc: James Morris <[email protected]>
Cc: Serge E. Hallyn <[email protected]>
Cc: Kentaro Takeda <[email protected]>
Cc: Tetsuo Handa <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Eric Biederman <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc:  <[email protected]>
Cc:  <[email protected]>
Cc:  <[email protected]>
Cc:  <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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;
 	}

security/tomoyo/tomoyo.c

@@ -328,7 +328,8 @@ 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)
+	/* Illogically, FMODE_EXEC is in f_flags, not f_mode. */
+	if (f->f_flags & __FMODE_EXEC)
 		return 0;
 	return tomoyo_check_open_permission(tomoyo_domain(), &f->f_path,
 					    f->f_flags);