apparmor: replace recursive profile removal with iterative approach

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: c88d4c7b049e ("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>

1 files changed, 27 insertions, 3 deletions

diff --git a/security/apparmor/policy.c b/security/apparmor/policy.c
index 9108d74c6b46..566821852592 100644
--- a/security/apparmor/policy.c
+++ b/security/apparmor/policy.c
@@ -191,19 +191,43 @@ 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);