apparmor: replace recursive profile removal with iterative approach

commit ab09264 upstream.

The profile removal code uses recursion when removing nested profiles,
which can lead to kernel stack exhaustion and system crashes.

Reproducer:
  $ pf='a'; for ((i=0; i<1024; i++)); do
      echo -e "profile $pf { \n }" | apparmor_parser -K -a;
      pf="$pf//x";
  done
  $ echo -n a > /sys/kernel/security/apparmor/.remove

Replace the recursive __aa_profile_list_release() approach with an
iterative approach in __remove_profile(). The function repeatedly
finds and removes leaf profiles until the entire subtree is removed,
maintaining the same removal semantic without recursion.

Fixes: c88d4c7 ("AppArmor: core policy routines")
Reported-by: Qualys Security Advisory <qsa@qualys.com>
Tested-by: Salvatore Bonaccorso <carnil@debian.org>
Reviewed-by: Georgia Garcia <georgia.garcia@canonical.com>
Reviewed-by: Cengiz Can <cengiz.can@canonical.com>
Signed-off-by: Massimiliano Pellizzer <massimiliano.pellizzer@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: m-pellizzer

security/apparmor/policy.c

@@ -184,19 +184,43 @@ static void __list_remove_profile(struct aa_profile *profile)
 }
 
 /**
- * __remove_profile - remove old profile, and children
- * @profile: profile to be replaced  (NOT NULL)
+ * __remove_profile - remove profile, and children
+ * @profile: profile to be removed  (NOT NULL)
  *
  * Requires: namespace list lock be held, or list not be shared
  */
 static void __remove_profile(struct aa_profile *profile)
 {
+	struct aa_profile *curr, *to_remove;
+
 	AA_BUG(!profile);
 	AA_BUG(!profile->ns);
 	AA_BUG(!mutex_is_locked(&profile->ns->lock));
 
 	/* release any children lists first */
-	__aa_profile_list_release(&profile->base.profiles);
+	if (!list_empty(&profile->base.profiles)) {
+		curr = list_first_entry(&profile->base.profiles, struct aa_profile, base.list);
+
+		while (curr != profile) {
+
+			while (!list_empty(&curr->base.profiles))
+				curr = list_first_entry(&curr->base.profiles,
+							struct aa_profile, base.list);
+
+			to_remove = curr;
+			if (!list_is_last(&to_remove->base.list,
+					  &aa_deref_parent(curr)->base.profiles))
+				curr = list_next_entry(to_remove, base.list);
+			else
+				curr = aa_deref_parent(curr);
+
+			/* released by free_profile */
+			aa_label_remove(&to_remove->label);
+			__aafs_profile_rmdir(to_remove);
+			__list_remove_profile(to_remove);
+		}
+	}
+
 	/* released by free_profile */
 	aa_label_remove(&profile->label);
 	__aafs_profile_rmdir(profile);