diff --git a/fs/richacl_compat.c b/fs/richacl_compat.c
index 2f6c32d..4f76cb9 100644
--- a/fs/richacl_compat.c
+++ b/fs/richacl_compat.c
@@ -413,3 +413,236 @@ richacl_propagate_everyone(struct richacl_alloc *x)
 	}
 	return 0;
 }
+
+/**
+ * richacl_max_allowed  -  maximum permissions that anybody is allowed
+ */
+static unsigned int
+richacl_max_allowed(struct richacl *acl)
+{
+	struct richace *ace;
+	unsigned int allowed = 0;
+
+	richacl_for_each_entry_reverse(ace, acl) {
+		if (richace_is_inherit_only(ace))
+			continue;
+		if (richace_is_allow(ace))
+			allowed |= ace->e_mask;
+		else if (richace_is_deny(ace)) {
+			if (richace_is_everyone(ace))
+				allowed &= ~ace->e_mask;
+		}
+	}
+	return allowed;
+}
+
+/**
+ * richacl_isolate_owner_class  -  limit the owner class to the owner file mask
+ * @x:		acl and number of allocated entries
+ *
+ * POSIX requires that after a chmod, the owner class is granted no more
+ * permissions than the owner file permission bits.  Mapped to richacls, this
+ * means that the owner class must not be granted any permissions that the
+ * owner mask does not include.
+ *
+ * When we apply file masks to an acl which grant more permissions to the group
+ * or other class than to the owner class, we may end up in a situation where
+ * the owner is granted additional permission from other aces.  For example,
+ * given this acl:
+ *
+ *    everyone:rwx::allow
+ *
+ * when file masks corresponding to mode 0466 are applied, after
+ * richacl_propagate_everyone() and __richacl_apply_masks(), we end up with:
+ *
+ *    owner@:r::allow
+ *    everyone@:rw::allow
+ *
+ * This acl still grants the owner rw access through the everyone@ allow ace.
+ * To fix this, we must deny w access to the owner:
+ *
+ *    owner@:w::deny
+ *    owner@:r::allow
+ *    everyone@:rw::allow
+ */
+static int
+richacl_isolate_owner_class(struct richacl_alloc *x)
+{
+	struct richace *ace;
+	unsigned int allowed = 0;
+
+	allowed = richacl_max_allowed(x->acl);
+	if (allowed & ~x->acl->a_owner_mask) {
+		/*
+		 * Figure out if we can update an existig OWNER@ DENY entry.
+		 */
+		richacl_for_each_entry(ace, x->acl) {
+			if (richace_is_inherit_only(ace))
+				continue;
+			if (richace_is_deny(ace)) {
+				if (richace_is_owner(ace))
+					break;
+			} else if (richace_is_allow(ace)) {
+				ace = x->acl->a_entries + x->acl->a_count;
+				break;
+			}
+		}
+		if (ace != x->acl->a_entries + x->acl->a_count) {
+			if (richace_change_mask(x, &ace, ace->e_mask |
+					(allowed & ~x->acl->a_owner_mask)))
+				return -1;
+		} else {
+			/* Insert an owner@ deny entry at the front. */
+			ace = x->acl->a_entries;
+			if (richacl_insert_entry(x, &ace))
+				return -1;
+			ace->e_type = RICHACE_ACCESS_DENIED_ACE_TYPE;
+			ace->e_flags = RICHACE_SPECIAL_WHO;
+			ace->e_mask = allowed & ~x->acl->a_owner_mask;
+			ace->e_id.special = RICHACE_OWNER_SPECIAL_ID;
+		}
+	}
+	return 0;
+}
+
+/**
+ * __richacl_isolate_who  -  isolate entry from everyone@ allow entry
+ * @x:		acl and number of allocated entries
+ * @who:	identifier to isolate
+ * @deny:	permissions this identifier should not be allowed
+ *
+ * See richacl_isolate_group_class().
+ */
+static int
+__richacl_isolate_who(struct richacl_alloc *x, struct richace *who,
+		      unsigned int deny)
+{
+	struct richace *ace;
+	unsigned int n;
+	/*
+	 * Compute the permissions already denied to @who.
+	 */
+	richacl_for_each_entry(ace, x->acl) {
+		if (richace_is_inherit_only(ace))
+			continue;
+		if (richace_is_same_identifier(ace, who) &&
+		    richace_is_deny(ace))
+			deny &= ~ace->e_mask;
+	}
+	if (!deny)
+		return 0;
+
+	/*
+	 * Figure out if we can update an existig deny entry.  Start from the
+	 * entry before the trailing everyone@ allow entry. We will not hit
+	 * everyone@ entries in the loop.
+	 */
+	for (n = x->acl->a_count - 2; n != -1; n--) {
+		ace = x->acl->a_entries + n;
+		if (richace_is_inherit_only(ace))
+			continue;
+		if (richace_is_deny(ace)) {
+			if (richace_is_same_identifier(ace, who))
+				break;
+		} else if (richace_is_allow(ace) &&
+			   (ace->e_mask & deny)) {
+			n = -1;
+			break;
+		}
+	}
+	if (n != -1) {
+		if (richace_change_mask(x, &ace, ace->e_mask | deny))
+			return -1;
+	} else {
+		/*
+		 * Insert a new entry before the trailing everyone@ deny entry.
+		 */
+		struct richace who_copy;
+
+		ace = x->acl->a_entries + x->acl->a_count - 1;
+		memcpy(&who_copy, who, sizeof(struct richace));
+		if (richacl_insert_entry(x, &ace))
+			return -1;
+		memcpy(ace, &who_copy, sizeof(struct richace));
+		ace->e_type = RICHACE_ACCESS_DENIED_ACE_TYPE;
+		richace_clear_inheritance_flags(ace);
+		ace->e_mask = deny;
+	}
+	return 0;
+}
+
+/**
+ * richacl_isolate_group_class  -  limit the group class to the group file mask
+ * @x:		acl and number of allocated entries
+ *
+ * POSIX requires that after a chmod, the group class is granted no more
+ * permissions than the group file permission bits.  Mapped to richacls, this
+ * means that the group class must not be granted any permissions that the
+ * group mask does not include.
+ *
+ * When we apply file masks to an acl which grant more permissions to the other
+ * class than to the group class, we may end up in a situation where processes
+ * in the group class are granted additional permission from other aces.  For
+ * example, given this acl:
+ *
+ *    joe:rwx::allow
+ *    everyone:rwx::allow
+ *
+ * when file masks corresponding to mode 0646 are applied, after
+ * richacl_propagate_everyone() and __richacl_apply_masks(), we end up with:
+ *
+ *    joe:r::allow
+ *    owner@:rw::allow
+ *    group@:r::allow
+ *    everyone@:rw::allow
+ *
+ * This acl still grants joe and group@ rw access through the everyone@ allow
+ * ace.  To fix this, we must deny w access to group class aces before the
+ * everyone@ allow ace at the end of the acl:
+ *
+ *    joe:r::allow
+ *    owner@:rw::allow
+ *    group@:r::allow
+ *    joe:w::deny
+ *    group@:w::deny
+ *    everyone@:rw::allow
+ */
+static int
+richacl_isolate_group_class(struct richacl_alloc *x)
+{
+	struct richace who = {
+		.e_flags = RICHACE_SPECIAL_WHO,
+		.e_id.special = RICHACE_GROUP_SPECIAL_ID,
+	};
+	struct richace *ace;
+	unsigned int deny;
+
+	if (!x->acl->a_count)
+		return 0;
+	ace = x->acl->a_entries + x->acl->a_count - 1;
+	if (richace_is_inherit_only(ace) || !richace_is_everyone(ace))
+		return 0;
+	deny = ace->e_mask & ~x->acl->a_group_mask;
+
+	if (deny) {
+		unsigned int n;
+
+		if (__richacl_isolate_who(x, &who, deny))
+			return -1;
+		/*
+		 * Start from the entry before the trailing everyone@ allow
+		 * entry.  We will not hit everyone@ entries in the loop.
+		 */
+		for (n = x->acl->a_count - 2; n != -1; n--) {
+			ace = x->acl->a_entries + n;
+
+			if (richace_is_inherit_only(ace) ||
+			    richace_is_owner(ace) ||
+			    richace_is_group(ace))
+				continue;
+			if (__richacl_isolate_who(x, ace, deny))
+				return -1;
+		}
+	}
+	return 0;
+}
