In preparation for better hierarchy support, it's needed to retain the local
settings in order to try to reapply them after a propagated change if they're
still valid.

v2: split this patch in two, one to just move dev_exception_rm() before
    dev_exception_add() while keeping functional changes in this patch as
    requested by Tejun.

Acked-by: Tejun Heo <tj@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Aristeu Rozanski <aris@redhat.com>
 
---
 security/device_cgroup.c |   83 +++++++++++++++++++++++++++++++++++++----------
 1 file changed, 67 insertions(+), 16 deletions(-)

--- github.orig/security/device_cgroup.c	2013-01-29 11:49:14.987661210 -0500
+++ github/security/device_cgroup.c	2013-01-29 11:49:15.244665037 -0500
@@ -39,13 +39,27 @@ struct dev_exception_item {
 	struct rcu_head rcu;
 };
 
+enum devcg_behavior {
+	DEVCG_DEFAULT_NONE,
+	DEVCG_DEFAULT_ALLOW,
+	DEVCG_DEFAULT_DENY,
+};
+
 struct dev_cgroup {
 	struct cgroup_subsys_state css;
+
+	/* result of merging the parent's rules with local ones */
 	struct list_head exceptions;
-	enum {
-		DEVCG_DEFAULT_ALLOW,
-		DEVCG_DEFAULT_DENY,
-	} behavior;
+	enum devcg_behavior behavior;
+
+	/*
+	 * local set rules, saved so when a parent propagates new rules, the
+	 * local preferences can be preserved
+	 */
+	struct {
+		struct list_head exceptions;
+		enum devcg_behavior behavior;
+	} local;
 };
 
 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
@@ -104,8 +118,8 @@ free_and_exit:
 /*
  * called under devcgroup_mutex
  */
-static void dev_exception_rm(struct list_head *exceptions,
-			     struct dev_exception_item *ex)
+static void __dev_exception_rm(struct list_head *exceptions,
+			       struct dev_exception_item *ex)
 {
 	struct dev_exception_item *walk, *tmp;
 
@@ -127,11 +141,18 @@ static void dev_exception_rm(struct list
 	}
 }
 
+static void dev_exception_rm(struct dev_cgroup *devcgroup,
+			     struct dev_exception_item *ex)
+{
+	__dev_exception_rm(&devcgroup->local.exceptions, ex);
+	__dev_exception_rm(&devcgroup->exceptions, ex);
+}
+
 /*
  * called under devcgroup_mutex
  */
-static int dev_exception_add(struct list_head *exceptions,
-			     struct dev_exception_item *ex)
+static int __dev_exception_add(struct list_head *exceptions,
+			       struct dev_exception_item *ex)
 {
 	struct dev_exception_item *excopy, *walk;
 
@@ -159,6 +180,28 @@ static int dev_exception_add(struct list
 	return 0;
 }
 
+static int dev_exception_add(struct dev_cgroup *devcgroup,
+			     struct dev_exception_item *ex)
+{
+	int rc;
+
+	lockdep_assert_held(&devcgroup_mutex);
+
+	/*
+	 * we add to the local list so we can preserve local preferences if
+	 * the parent propagates down new rules
+	 */
+	rc = __dev_exception_add(&devcgroup->local.exceptions, ex);
+	if (rc)
+		return rc;
+
+	rc = __dev_exception_add(&devcgroup->exceptions, ex);
+	if (rc)
+		__dev_exception_rm(&devcgroup->local.exceptions, ex);
+
+	return rc;
+}
+
 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
 {
 	struct dev_exception_item *ex, *tmp;
@@ -167,6 +210,11 @@ static void __dev_exception_clean(struct
 		list_del_rcu(&ex->list);
 		kfree_rcu(ex, rcu);
 	}
+	list_for_each_entry_safe(ex, tmp, &dev_cgroup->local.exceptions,
+				 list) {
+		list_del_rcu(&ex->list);
+		kfree_rcu(ex, rcu);
+	}
 }
 
 /**
@@ -195,6 +243,8 @@ static struct cgroup_subsys_state *devcg
 	if (!dev_cgroup)
 		return ERR_PTR(-ENOMEM);
 	INIT_LIST_HEAD(&dev_cgroup->exceptions);
+	INIT_LIST_HEAD(&dev_cgroup->local.exceptions);
+	dev_cgroup->local.behavior = DEVCG_DEFAULT_NONE;
 	parent_cgroup = cgroup->parent;
 
 	if (parent_cgroup == NULL)
@@ -413,18 +463,19 @@ 	memset(&ex, 0, sizeof(ex));
 			if (!may_allow_all(parent))
 				return -EPERM;
 			dev_exception_clean(devcgroup);
+			if (parent)
+				rc = dev_exceptions_copy(&devcgroup->exceptions,
+							 &parent->exceptions);
 			devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
-			if (!parent)
-				break;
+			devcgroup->local.behavior = DEVCG_DEFAULT_ALLOW;
 
-			rc = dev_exceptions_copy(&devcgroup->exceptions,
-						 &parent->exceptions);
 			if (rc)
 				return rc;
 			break;
 		case DEVCG_DENY:
 			dev_exception_clean(devcgroup);
 			devcgroup->behavior = DEVCG_DEFAULT_DENY;
+			devcgroup->local.behavior = DEVCG_DEFAULT_DENY;
 			break;
 		default:
 			return -EINVAL;
@@ -514,10 +565,10 @@ 		case '\0':
 		 * don't want to break compatibility
 		 */
 		if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
-			dev_exception_rm(&devcgroup->exceptions, &ex);
+			dev_exception_rm(devcgroup, &ex);
 			return 0;
 		}
-		return dev_exception_add(&devcgroup->exceptions, &ex);
+		return dev_exception_add(devcgroup, &ex);
 	case DEVCG_DENY:
 		/*
 		 * If the default policy is to deny by default, try to remove
@@ -525,10 +576,10 @@ 			return 0;
 		 * don't want to break compatibility
 		 */
 		if (devcgroup->behavior == DEVCG_DEFAULT_DENY) {
-			dev_exception_rm(&devcgroup->exceptions, &ex);
+			dev_exception_rm(devcgroup, &ex);
 			return 0;
 		}
-		return dev_exception_add(&devcgroup->exceptions, &ex);
+		return dev_exception_add(devcgroup, &ex);
 	default:
 		return -EINVAL;
 	}

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