1 files changed, 360 insertions, 142 deletions

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index d794abcc4b3..d9d69e6930e 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -25,6 +25,12 @@
 
 static DEFINE_MUTEX(devcgroup_mutex);
 
+enum devcg_behavior {
+	DEVCG_DEFAULT_NONE,
+	DEVCG_DEFAULT_ALLOW,
+	DEVCG_DEFAULT_DENY,
+};
+
 /*
  * exception list locking rules:
  * hold devcgroup_mutex for update/read.
@@ -42,37 +48,17 @@ struct dev_exception_item {
 struct dev_cgroup {
 	struct cgroup_subsys_state css;
 	struct list_head exceptions;
-	enum {
-		DEVCG_DEFAULT_ALLOW,
-		DEVCG_DEFAULT_DENY,
-	} behavior;
+	enum devcg_behavior behavior;
 };
 
 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
 {
-	return container_of(s, struct dev_cgroup, css);
-}
-
-static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
-{
-	return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
+	return s ? container_of(s, struct dev_cgroup, css) : NULL;
 }
 
 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
 {
-	return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
-}
-
-struct cgroup_subsys devices_subsys;
-
-static int devcgroup_can_attach(struct cgroup *new_cgrp,
-				struct cgroup_taskset *set)
-{
-	struct task_struct *task = cgroup_taskset_first(set);
-
-	if (current != task && !capable(CAP_SYS_ADMIN))
-		return -EPERM;
-	return 0;
+	return css_to_devcgroup(task_css(task, devices_cgrp_id));
 }
 
 /*
@@ -159,6 +145,16 @@ static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
 	}
 }
 
+static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
+{
+	struct dev_exception_item *ex, *tmp;
+
+	list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
+		list_del_rcu(&ex->list);
+		kfree_rcu(ex, rcu);
+	}
+}
+
 /**
  * dev_exception_clean - frees all entries of the exception list
  * @dev_cgroup: dev_cgroup with the exception list to be cleaned
@@ -167,57 +163,74 @@ static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
  */
 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
 {
-	struct dev_exception_item *ex, *tmp;
-
 	lockdep_assert_held(&devcgroup_mutex);
 
-	list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
-		list_del_rcu(&ex->list);
-		kfree_rcu(ex, rcu);
-	}
+	__dev_exception_clean(dev_cgroup);
 }
 
-/*
- * called from kernel/cgroup.c with cgroup_lock() held.
+static inline bool is_devcg_online(const struct dev_cgroup *devcg)
+{
+	return (devcg->behavior != DEVCG_DEFAULT_NONE);
+}
+
+/**
+ * devcgroup_online - initializes devcgroup's behavior and exceptions based on
+ * 		      parent's
+ * @css: css getting online
+ * returns 0 in case of success, error code otherwise
  */
-static struct cgroup_subsys_state *devcgroup_css_alloc(struct cgroup *cgroup)
+static int devcgroup_online(struct cgroup_subsys_state *css)
 {
-	struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
-	struct cgroup *parent_cgroup;
-	int ret;
+	struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
+	struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent);
+	int ret = 0;
 
-	dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
-	if (!dev_cgroup)
-		return ERR_PTR(-ENOMEM);
-	INIT_LIST_HEAD(&dev_cgroup->exceptions);
-	parent_cgroup = cgroup->parent;
+	mutex_lock(&devcgroup_mutex);
 
-	if (parent_cgroup == NULL)
+	if (parent_dev_cgroup == NULL)
 		dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
 	else {
-		parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
-		mutex_lock(&devcgroup_mutex);
 		ret = dev_exceptions_copy(&dev_cgroup->exceptions,
 					  &parent_dev_cgroup->exceptions);
-		dev_cgroup->behavior = parent_dev_cgroup->behavior;
-		mutex_unlock(&devcgroup_mutex);
-		if (ret) {
-			kfree(dev_cgroup);
-			return ERR_PTR(ret);
-		}
+		if (!ret)
+			dev_cgroup->behavior = parent_dev_cgroup->behavior;
 	}
+	mutex_unlock(&devcgroup_mutex);
 
-	return &dev_cgroup->css;
+	return ret;
 }
 
-static void devcgroup_css_free(struct cgroup *cgroup)
+static void devcgroup_offline(struct cgroup_subsys_state *css)
 {
-	struct dev_cgroup *dev_cgroup;
+	struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
 
-	dev_cgroup = cgroup_to_devcgroup(cgroup);
 	mutex_lock(&devcgroup_mutex);
-	dev_exception_clean(dev_cgroup);
+	dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
 	mutex_unlock(&devcgroup_mutex);
+}
+
+/*
+ * called from kernel/cgroup.c with cgroup_lock() held.
+ */
+static struct cgroup_subsys_state *
+devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
+{
+	struct dev_cgroup *dev_cgroup;
+
+	dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
+	if (!dev_cgroup)
+		return ERR_PTR(-ENOMEM);
+	INIT_LIST_HEAD(&dev_cgroup->exceptions);
+	dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
+
+	return &dev_cgroup->css;
+}
+
+static void devcgroup_css_free(struct cgroup_subsys_state *css)
+{
+	struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
+
+	__dev_exception_clean(dev_cgroup);
 	kfree(dev_cgroup);
 }
 
@@ -259,10 +272,9 @@ static void set_majmin(char *str, unsigned m)
 		sprintf(str, "%u", m);
 }
 
-static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
-				struct seq_file *m)
+static int devcgroup_seq_show(struct seq_file *m, void *v)
 {
-	struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
+	struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
 	struct dev_exception_item *ex;
 	char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
 
@@ -294,51 +306,145 @@ static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
 }
 
 /**
- * may_access - verifies if a new exception is part of what is allowed
- *		by a dev cgroup based on the default policy +
- *		exceptions. This is used to make sure a child cgroup
- *		won't have more privileges than its parent or to
- *		verify if a certain access is allowed.
- * @dev_cgroup: dev cgroup to be tested against
- * @refex: new exception
+ * match_exception	- iterates the exception list trying to find a complete match
+ * @exceptions: list of exceptions
+ * @type: device type (DEV_BLOCK or DEV_CHAR)
+ * @major: device file major number, ~0 to match all
+ * @minor: device file minor number, ~0 to match all
+ * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
+ *
+ * It is considered a complete match if an exception is found that will
+ * contain the entire range of provided parameters.
+ *
+ * Return: true in case it matches an exception completely
  */
-static int may_access(struct dev_cgroup *dev_cgroup,
-		      struct dev_exception_item *refex)
+static bool match_exception(struct list_head *exceptions, short type,
+			    u32 major, u32 minor, short access)
 {
 	struct dev_exception_item *ex;
-	bool match = false;
 
-	rcu_lockdep_assert(rcu_read_lock_held() ||
-			   lockdep_is_held(&devcgroup_mutex),
-			   "device_cgroup::may_access() called without proper synchronization");
+	list_for_each_entry_rcu(ex, exceptions, list) {
+		if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
+			continue;
+		if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
+			continue;
+		if (ex->major != ~0 && ex->major != major)
+			continue;
+		if (ex->minor != ~0 && ex->minor != minor)
+			continue;
+		/* provided access cannot have more than the exception rule */
+		if (access & (~ex->access))
+			continue;
+		return true;
+	}
+	return false;
+}
+
+/**
+ * match_exception_partial - iterates the exception list trying to find a partial match
+ * @exceptions: list of exceptions
+ * @type: device type (DEV_BLOCK or DEV_CHAR)
+ * @major: device file major number, ~0 to match all
+ * @minor: device file minor number, ~0 to match all
+ * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
+ *
+ * It is considered a partial match if an exception's range is found to
+ * contain *any* of the devices specified by provided parameters. This is
+ * used to make sure no extra access is being granted that is forbidden by
+ * any of the exception list.
+ *
+ * Return: true in case the provided range mat matches an exception completely
+ */
+static bool match_exception_partial(struct list_head *exceptions, short type,
+				    u32 major, u32 minor, short access)
+{
+	struct dev_exception_item *ex;
 
-	list_for_each_entry_rcu(ex, &dev_cgroup->exceptions, list) {
-		if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
+	list_for_each_entry_rcu(ex, exceptions, list) {
+		if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
 			continue;
-		if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR))
+		if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
 			continue;
-		if (ex->major != ~0 && ex->major != refex->major)
+		/*
+		 * We must be sure that both the exception and the provided
+		 * range aren't masking all devices
+		 */
+		if (ex->major != ~0 && major != ~0 && ex->major != major)
 			continue;
-		if (ex->minor != ~0 && ex->minor != refex->minor)
+		if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
 			continue;
-		if (refex->access & (~ex->access))
+		/*
+		 * In order to make sure the provided range isn't matching
+		 * an exception, all its access bits shouldn't match the
+		 * exception's access bits
+		 */
+		if (!(access & ex->access))
 			continue;
-		match = true;
-		break;
+		return true;
 	}
+	return false;
+}
 
-	/*
-	 * In two cases we'll consider this new exception valid:
-	 * - the dev cgroup has its default policy to allow + exception list:
-	 *   the new exception should *not* match any of the exceptions
-	 *   (behavior == DEVCG_DEFAULT_ALLOW, !match)
-	 * - the dev cgroup has its default policy to deny + exception list:
-	 *   the new exception *should* match the exceptions
-	 *   (behavior == DEVCG_DEFAULT_DENY, match)
-	 */
-	if ((dev_cgroup->behavior == DEVCG_DEFAULT_DENY) == match)
-		return 1;
-	return 0;
+/**
+ * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions
+ * @dev_cgroup: dev cgroup to be tested against
+ * @refex: new exception
+ * @behavior: behavior of the exception's dev_cgroup
+ *
+ * This is used to make sure a child cgroup won't have more privileges
+ * than its parent
+ */
+static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
+		          struct dev_exception_item *refex,
+		          enum devcg_behavior behavior)
+{
+	bool match = false;
+
+	rcu_lockdep_assert(rcu_read_lock_held() ||
+			   lockdep_is_held(&devcgroup_mutex),
+			   "device_cgroup:verify_new_ex called without proper synchronization");
+
+	if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
+		if (behavior == DEVCG_DEFAULT_ALLOW) {
+			/*
+			 * new exception in the child doesn't matter, only
+			 * adding extra restrictions
+			 */ 
+			return true;
+		} else {
+			/*
+			 * new exception in the child will add more devices
+			 * that can be acessed, so it can't match any of
+			 * parent's exceptions, even slightly
+			 */ 
+			match = match_exception_partial(&dev_cgroup->exceptions,
+							refex->type,
+							refex->major,
+							refex->minor,
+							refex->access);
+
+			if (match)
+				return false;
+			return true;
+		}
+	} else {
+		/*
+		 * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore
+		 * the new exception will add access to more devices and must
+		 * be contained completely in an parent's exception to be
+		 * allowed
+		 */
+		match = match_exception(&dev_cgroup->exceptions, refex->type,
+					refex->major, refex->minor,
+					refex->access);
+
+		if (match)
+			/* parent has an exception that matches the proposed */
+			return true;
+		else
+			return false;
+	}
+	return false;
 }
 
 /*
@@ -349,13 +455,42 @@ static int may_access(struct dev_cgroup *dev_cgroup,
 static int parent_has_perm(struct dev_cgroup *childcg,
 				  struct dev_exception_item *ex)
 {
-	struct cgroup *pcg = childcg->css.cgroup->parent;
-	struct dev_cgroup *parent;
+	struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
 
-	if (!pcg)
+	if (!parent)
 		return 1;
-	parent = cgroup_to_devcgroup(pcg);
-	return may_access(parent, ex);
+	return verify_new_ex(parent, ex, childcg->behavior);
+}
+
+/**
+ * parent_allows_removal - verify if it's ok to remove an exception
+ * @childcg: child cgroup from where the exception will be removed
+ * @ex: exception being removed
+ *
+ * When removing an exception in cgroups with default ALLOW policy, it must
+ * be checked if removing it will give the child cgroup more access than the
+ * parent.
+ *
+ * Return: true if it's ok to remove exception, false otherwise
+ */
+static bool parent_allows_removal(struct dev_cgroup *childcg,
+				  struct dev_exception_item *ex)
+{
+	struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
+
+	if (!parent)
+		return true;
+
+	/* It's always allowed to remove access to devices */
+	if (childcg->behavior == DEVCG_DEFAULT_DENY)
+		return true;
+
+	/*
+	 * Make sure you're not removing part or a whole exception existing in
+	 * the parent cgroup
+	 */
+	return !match_exception_partial(&parent->exceptions, ex->type,
+					ex->major, ex->minor, ex->access);
 }
 
 /**
@@ -371,6 +506,87 @@ static inline int may_allow_all(struct dev_cgroup *parent)
 	return parent->behavior == DEVCG_DEFAULT_ALLOW;
 }
 
+/**
+ * revalidate_active_exceptions - walks through the active exception list and
+ * 				  revalidates the exceptions based on parent's
+ * 				  behavior and exceptions. The exceptions that
+ * 				  are no longer valid will be removed.
+ * 				  Called with devcgroup_mutex held.
+ * @devcg: cgroup which exceptions will be checked
+ *
+ * This is one of the three key functions for hierarchy implementation.
+ * This function is responsible for re-evaluating all the cgroup's active
+ * exceptions due to a parent's exception change.
+ * Refer to Documentation/cgroups/devices.txt for more details.
+ */
+static void revalidate_active_exceptions(struct dev_cgroup *devcg)
+{
+	struct dev_exception_item *ex;
+	struct list_head *this, *tmp;
+
+	list_for_each_safe(this, tmp, &devcg->exceptions) {
+		ex = container_of(this, struct dev_exception_item, list);
+		if (!parent_has_perm(devcg, ex))
+			dev_exception_rm(devcg, ex);
+	}
+}
+
+/**
+ * propagate_exception - propagates a new exception to the children
+ * @devcg_root: device cgroup that added a new exception
+ * @ex: new exception to be propagated
+ *
+ * returns: 0 in case of success, != 0 in case of error
+ */
+static int propagate_exception(struct dev_cgroup *devcg_root,
+			       struct dev_exception_item *ex)
+{
+	struct cgroup_subsys_state *pos;
+	int rc = 0;
+
+	rcu_read_lock();
+
+	css_for_each_descendant_pre(pos, &devcg_root->css) {
+		struct dev_cgroup *devcg = css_to_devcgroup(pos);
+
+		/*
+		 * Because devcgroup_mutex is held, no devcg will become
+		 * online or offline during the tree walk (see on/offline
+		 * methods), and online ones are safe to access outside RCU
+		 * read lock without bumping refcnt.
+		 */
+		if (pos == &devcg_root->css || !is_devcg_online(devcg))
+			continue;
+
+		rcu_read_unlock();
+
+		/*
+		 * in case both root's behavior and devcg is allow, a new
+		 * restriction means adding to the exception list
+		 */
+		if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
+		    devcg->behavior == DEVCG_DEFAULT_ALLOW) {
+			rc = dev_exception_add(devcg, ex);
+			if (rc)
+				break;
+		} else {
+			/*
+			 * in the other possible cases:
+			 * root's behavior: allow, devcg's: deny
+			 * root's behavior: deny, devcg's: deny
+			 * the exception will be removed
+			 */
+			dev_exception_rm(devcg, ex);
+		}
+		revalidate_active_exceptions(devcg);
+
+		rcu_read_lock();
+	}
+
+	rcu_read_unlock();
+	return rc;
+}
+
 /*
  * Modify the exception list using allow/deny rules.
  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
@@ -385,21 +601,17 @@ static inline int may_allow_all(struct dev_cgroup *parent)
  * parent cgroup has the access you're asking for.
  */
 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
-				   int filetype, const char *buffer)
+				   int filetype, char *buffer)
 {
 	const char *b;
 	char temp[12];		/* 11 + 1 characters needed for a u32 */
-	int count, rc;
+	int count, rc = 0;
 	struct dev_exception_item ex;
-	struct cgroup *p = devcgroup->css.cgroup;
-	struct dev_cgroup *parent = NULL;
+	struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	if (p->parent)
-		parent = cgroup_to_devcgroup(p->parent);
-
 	memset(&ex, 0, sizeof(ex));
 	b = buffer;
 
@@ -407,6 +619,9 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 	case 'a':
 		switch (filetype) {
 		case DEVCG_ALLOW:
+			if (css_has_online_children(&devcgroup->css))
+				return -EINVAL;
+
 			if (!may_allow_all(parent))
 				return -EPERM;
 			dev_exception_clean(devcgroup);
@@ -420,6 +635,9 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 				return rc;
 			break;
 		case DEVCG_DENY:
+			if (css_has_online_children(&devcgroup->css))
+				return -EINVAL;
+
 			dev_exception_clean(devcgroup);
 			devcgroup->behavior = DEVCG_DEFAULT_DENY;
 			break;
@@ -503,82 +721,82 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 
 	switch (filetype) {
 	case DEVCG_ALLOW:
-		if (!parent_has_perm(devcgroup, &ex))
-			return -EPERM;
 		/*
 		 * If the default policy is to allow by default, try to remove
 		 * an matching exception instead. And be silent about it: we
 		 * don't want to break compatibility
 		 */
 		if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
+			/* Check if the parent allows removing it first */
+			if (!parent_allows_removal(devcgroup, &ex))
+				return -EPERM;
 			dev_exception_rm(devcgroup, &ex);
-			return 0;
+			break;
 		}
-		return dev_exception_add(devcgroup, &ex);
+
+		if (!parent_has_perm(devcgroup, &ex))
+			return -EPERM;
+		rc = dev_exception_add(devcgroup, &ex);
+		break;
 	case DEVCG_DENY:
 		/*
 		 * If the default policy is to deny by default, try to remove
 		 * an matching exception instead. And be silent about it: we
 		 * don't want to break compatibility
 		 */
-		if (devcgroup->behavior == DEVCG_DEFAULT_DENY) {
+		if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
 			dev_exception_rm(devcgroup, &ex);
-			return 0;
-		}
-		return dev_exception_add(devcgroup, &ex);
+		else
+			rc = dev_exception_add(devcgroup, &ex);
+
+		if (rc)
+			break;
+		/* we only propagate new restrictions */
+		rc = propagate_exception(devcgroup, &ex);
+		break;
 	default:
-		return -EINVAL;
+		rc = -EINVAL;
 	}
-	return 0;
+	return rc;
 }
 
-static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
-				  const char *buffer)
+static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
+				      char *buf, size_t nbytes, loff_t off)
 {
 	int retval;
 
 	mutex_lock(&devcgroup_mutex);
-	retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
-					 cft->private, buffer);
+	retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
+					 of_cft(of)->private, strstrip(buf));
 	mutex_unlock(&devcgroup_mutex);
-	return retval;
+	return retval ?: nbytes;
 }
 
 static struct cftype dev_cgroup_files[] = {
 	{
 		.name = "allow",
-		.write_string  = devcgroup_access_write,
+		.write = devcgroup_access_write,
 		.private = DEVCG_ALLOW,
 	},
 	{
 		.name = "deny",
-		.write_string = devcgroup_access_write,
+		.write = devcgroup_access_write,
 		.private = DEVCG_DENY,
 	},
 	{
 		.name = "list",
-		.read_seq_string = devcgroup_seq_read,
+		.seq_show = devcgroup_seq_show,
 		.private = DEVCG_LIST,
 	},
 	{ }	/* terminate */
 };
 
-struct cgroup_subsys devices_subsys = {
-	.name = "devices",
-	.can_attach = devcgroup_can_attach,
+struct cgroup_subsys devices_cgrp_subsys = {
 	.css_alloc = devcgroup_css_alloc,
 	.css_free = devcgroup_css_free,
-	.subsys_id = devices_subsys_id,
+	.css_online = devcgroup_online,
+	.css_offline = devcgroup_offline,
 	.base_cftypes = dev_cgroup_files,
-
-	/*
-	 * While devices cgroup has the rudimentary hierarchy support which
-	 * checks the parent's restriction, it doesn't properly propagates
-	 * config changes in ancestors to their descendents.  A child
-	 * should only be allowed to add more restrictions to the parent's
-	 * configuration.  Fix it and remove the following.
-	 */
-	.broken_hierarchy = true,
 };
 
 /**
@@ -595,18 +813,18 @@ static int __devcgroup_check_permission(short type, u32 major, u32 minor,
 				        short access)
 {
 	struct dev_cgroup *dev_cgroup;
-	struct dev_exception_item ex;
-	int rc;
-
-	memset(&ex, 0, sizeof(ex));
-	ex.type = type;
-	ex.major = major;
-	ex.minor = minor;
-	ex.access = access;
+	bool rc;
 
 	rcu_read_lock();
 	dev_cgroup = task_devcgroup(current);
-	rc = may_access(dev_cgroup, &ex);
+	if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
+		/* Can't match any of the exceptions, even partially */
+		rc = !match_exception_partial(&dev_cgroup->exceptions,
+					      type, major, minor, access);
+	else
+		/* Need to match completely one exception to be allowed */
+		rc = match_exception(&dev_cgroup->exceptions, type, major,
+				     minor, access);
 	rcu_read_unlock();
 
 	if (!rc)