Initial import

1 files changed, 870 insertions, 0 deletions

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
new file mode 100644
index 000000000..426d9af14
--- /dev/null
+++ b/security/device_cgroup.c
@@ -0,0 +1,870 @@
+/*
+ * device_cgroup.c - device cgroup subsystem
+ *
+ * Copyright 2007 IBM Corp
+ */
+
+#include <linux/device_cgroup.h>
+#include <linux/cgroup.h>
+#include <linux/ctype.h>
+#include <linux/export.h>
+#include <linux/list.h>
+#include <linux/uaccess.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include <linux/rcupdate.h>
+#include <linux/mutex.h>
+
+#define ACC_MKNOD 1
+#define ACC_READ  2
+#define ACC_WRITE 4
+#define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
+
+#define DEV_BLOCK 1
+#define DEV_CHAR  2
+#define DEV_ALL   4  /* this represents all devices */
+
+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.
+ * hold rcu_read_lock() for read.
+ */
+
+struct dev_exception_item {
+	u32 major, minor;
+	short type;
+	short access;
+	struct list_head list;
+	struct rcu_head rcu;
+};
+
+struct dev_cgroup {
+	struct cgroup_subsys_state css;
+	struct list_head exceptions;
+	enum devcg_behavior behavior;
+};
+
+static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
+{
+	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_css(task, devices_cgrp_id));
+}
+
+/*
+ * called under devcgroup_mutex
+ */
+static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
+{
+	struct dev_exception_item *ex, *tmp, *new;
+
+	lockdep_assert_held(&devcgroup_mutex);
+
+	list_for_each_entry(ex, orig, list) {
+		new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
+		if (!new)
+			goto free_and_exit;
+		list_add_tail(&new->list, dest);
+	}
+
+	return 0;
+
+free_and_exit:
+	list_for_each_entry_safe(ex, tmp, dest, list) {
+		list_del(&ex->list);
+		kfree(ex);
+	}
+	return -ENOMEM;
+}
+
+/*
+ * called under devcgroup_mutex
+ */
+static int dev_exception_add(struct dev_cgroup *dev_cgroup,
+			     struct dev_exception_item *ex)
+{
+	struct dev_exception_item *excopy, *walk;
+
+	lockdep_assert_held(&devcgroup_mutex);
+
+	excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
+	if (!excopy)
+		return -ENOMEM;
+
+	list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
+		if (walk->type != ex->type)
+			continue;
+		if (walk->major != ex->major)
+			continue;
+		if (walk->minor != ex->minor)
+			continue;
+
+		walk->access |= ex->access;
+		kfree(excopy);
+		excopy = NULL;
+	}
+
+	if (excopy != NULL)
+		list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
+	return 0;
+}
+
+/*
+ * called under devcgroup_mutex
+ */
+static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
+			     struct dev_exception_item *ex)
+{
+	struct dev_exception_item *walk, *tmp;
+
+	lockdep_assert_held(&devcgroup_mutex);
+
+	list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
+		if (walk->type != ex->type)
+			continue;
+		if (walk->major != ex->major)
+			continue;
+		if (walk->minor != ex->minor)
+			continue;
+
+		walk->access &= ~ex->access;
+		if (!walk->access) {
+			list_del_rcu(&walk->list);
+			kfree_rcu(walk, rcu);
+		}
+	}
+}
+
+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
+ *
+ * called under devcgroup_mutex
+ */
+static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
+{
+	lockdep_assert_held(&devcgroup_mutex);
+
+	__dev_exception_clean(dev_cgroup);
+}
+
+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 int devcgroup_online(struct cgroup_subsys_state *css)
+{
+	struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
+	struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent);
+	int ret = 0;
+
+	mutex_lock(&devcgroup_mutex);
+
+	if (parent_dev_cgroup == NULL)
+		dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
+	else {
+		ret = dev_exceptions_copy(&dev_cgroup->exceptions,
+					  &parent_dev_cgroup->exceptions);
+		if (!ret)
+			dev_cgroup->behavior = parent_dev_cgroup->behavior;
+	}
+	mutex_unlock(&devcgroup_mutex);
+
+	return ret;
+}
+
+static void devcgroup_offline(struct cgroup_subsys_state *css)
+{
+	struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
+
+	mutex_lock(&devcgroup_mutex);
+	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);
+}
+
+#define DEVCG_ALLOW 1
+#define DEVCG_DENY 2
+#define DEVCG_LIST 3
+
+#define MAJMINLEN 13
+#define ACCLEN 4
+
+static void set_access(char *acc, short access)
+{
+	int idx = 0;
+	memset(acc, 0, ACCLEN);
+	if (access & ACC_READ)
+		acc[idx++] = 'r';
+	if (access & ACC_WRITE)
+		acc[idx++] = 'w';
+	if (access & ACC_MKNOD)
+		acc[idx++] = 'm';
+}
+
+static char type_to_char(short type)
+{
+	if (type == DEV_ALL)
+		return 'a';
+	if (type == DEV_CHAR)
+		return 'c';
+	if (type == DEV_BLOCK)
+		return 'b';
+	return 'X';
+}
+
+static void set_majmin(char *str, unsigned m)
+{
+	if (m == ~0)
+		strcpy(str, "*");
+	else
+		sprintf(str, "%u", m);
+}
+
+static int devcgroup_seq_show(struct seq_file *m, void *v)
+{
+	struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
+	struct dev_exception_item *ex;
+	char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
+
+	rcu_read_lock();
+	/*
+	 * To preserve the compatibility:
+	 * - Only show the "all devices" when the default policy is to allow
+	 * - List the exceptions in case the default policy is to deny
+	 * This way, the file remains as a "whitelist of devices"
+	 */
+	if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
+		set_access(acc, ACC_MASK);
+		set_majmin(maj, ~0);
+		set_majmin(min, ~0);
+		seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL),
+			   maj, min, acc);
+	} else {
+		list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
+			set_access(acc, ex->access);
+			set_majmin(maj, ex->major);
+			set_majmin(min, ex->minor);
+			seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
+				   maj, min, acc);
+		}
+	}
+	rcu_read_unlock();
+
+	return 0;
+}
+
+/**
+ * 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 bool match_exception(struct list_head *exceptions, short type,
+			    u32 major, u32 minor, short access)
+{
+	struct dev_exception_item *ex;
+
+	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, exceptions, list) {
+		if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
+			continue;
+		if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
+			continue;
+		/*
+		 * 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 && minor != ~0 && ex->minor != minor)
+			continue;
+		/*
+		 * 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;
+		return true;
+	}
+	return false;
+}
+
+/**
+ * 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;
+}
+
+/*
+ * parent_has_perm:
+ * when adding a new allow rule to a device exception list, the rule
+ * must be allowed in the parent device
+ */
+static int parent_has_perm(struct dev_cgroup *childcg,
+				  struct dev_exception_item *ex)
+{
+	struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
+
+	if (!parent)
+		return 1;
+	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);
+}
+
+/**
+ * may_allow_all - checks if it's possible to change the behavior to
+ *		   allow based on parent's rules.
+ * @parent: device cgroup's parent
+ * returns: != 0 in case it's allowed, 0 otherwise
+ */
+static inline int may_allow_all(struct dev_cgroup *parent)
+{
+	if (!parent)
+		return 1;
+	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
+ * so we can give a container CAP_MKNOD to let it create devices but not
+ * modify the exception list.
+ * It seems likely we'll want to add a CAP_CONTAINER capability to allow
+ * us to also grant CAP_SYS_ADMIN to containers without giving away the
+ * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
+ *
+ * Taking rules away is always allowed (given CAP_SYS_ADMIN).  Granting
+ * new access is only allowed if you're in the top-level cgroup, or your
+ * parent cgroup has the access you're asking for.
+ */
+static int devcgroup_update_access(struct dev_cgroup *devcgroup,
+				   int filetype, char *buffer)
+{
+	const char *b;
+	char temp[12];		/* 11 + 1 characters needed for a u32 */
+	int count, rc = 0;
+	struct dev_exception_item ex;
+	struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	memset(&ex, 0, sizeof(ex));
+	b = buffer;
+
+	switch (*b) {
+	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);
+			devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
+			if (!parent)
+				break;
+
+			rc = dev_exceptions_copy(&devcgroup->exceptions,
+						 &parent->exceptions);
+			if (rc)
+				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;
+		default:
+			return -EINVAL;
+		}
+		return 0;
+	case 'b':
+		ex.type = DEV_BLOCK;
+		break;
+	case 'c':
+		ex.type = DEV_CHAR;
+		break;
+	default:
+		return -EINVAL;
+	}
+	b++;
+	if (!isspace(*b))
+		return -EINVAL;
+	b++;
+	if (*b == '*') {
+		ex.major = ~0;
+		b++;
+	} else if (isdigit(*b)) {
+		memset(temp, 0, sizeof(temp));
+		for (count = 0; count < sizeof(temp) - 1; count++) {
+			temp[count] = *b;
+			b++;
+			if (!isdigit(*b))
+				break;
+		}
+		rc = kstrtou32(temp, 10, &ex.major);
+		if (rc)
+			return -EINVAL;
+	} else {
+		return -EINVAL;
+	}
+	if (*b != ':')
+		return -EINVAL;
+	b++;
+
+	/* read minor */
+	if (*b == '*') {
+		ex.minor = ~0;
+		b++;
+	} else if (isdigit(*b)) {
+		memset(temp, 0, sizeof(temp));
+		for (count = 0; count < sizeof(temp) - 1; count++) {
+			temp[count] = *b;
+			b++;
+			if (!isdigit(*b))
+				break;
+		}
+		rc = kstrtou32(temp, 10, &ex.minor);
+		if (rc)
+			return -EINVAL;
+	} else {
+		return -EINVAL;
+	}
+	if (!isspace(*b))
+		return -EINVAL;
+	for (b++, count = 0; count < 3; count++, b++) {
+		switch (*b) {
+		case 'r':
+			ex.access |= ACC_READ;
+			break;
+		case 'w':
+			ex.access |= ACC_WRITE;
+			break;
+		case 'm':
+			ex.access |= ACC_MKNOD;
+			break;
+		case '\n':
+		case '\0':
+			count = 3;
+			break;
+		default:
+			return -EINVAL;
+		}
+	}
+
+	switch (filetype) {
+	case DEVCG_ALLOW:
+		/*
+		 * 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);
+			break;
+		}
+
+		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)
+			dev_exception_rm(devcgroup, &ex);
+		else
+			rc = dev_exception_add(devcgroup, &ex);
+
+		if (rc)
+			break;
+		/* we only propagate new restrictions */
+		rc = propagate_exception(devcgroup, &ex);
+		break;
+	default:
+		rc = -EINVAL;
+	}
+	return rc;
+}
+
+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(css_to_devcgroup(of_css(of)),
+					 of_cft(of)->private, strstrip(buf));
+	mutex_unlock(&devcgroup_mutex);
+	return retval ?: nbytes;
+}
+
+static struct cftype dev_cgroup_files[] = {
+	{
+		.name = "allow",
+		.write = devcgroup_access_write,
+		.private = DEVCG_ALLOW,
+	},
+	{
+		.name = "deny",
+		.write = devcgroup_access_write,
+		.private = DEVCG_DENY,
+	},
+	{
+		.name = "list",
+		.seq_show = devcgroup_seq_show,
+		.private = DEVCG_LIST,
+	},
+	{ }	/* terminate */
+};
+
+struct cgroup_subsys devices_cgrp_subsys = {
+	.css_alloc = devcgroup_css_alloc,
+	.css_free = devcgroup_css_free,
+	.css_online = devcgroup_online,
+	.css_offline = devcgroup_offline,
+	.legacy_cftypes = dev_cgroup_files,
+};
+
+/**
+ * __devcgroup_check_permission - checks if an inode operation is permitted
+ * @dev_cgroup: the dev cgroup to be tested against
+ * @type: device type
+ * @major: device major number
+ * @minor: device minor number
+ * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
+ *
+ * returns 0 on success, -EPERM case the operation is not permitted
+ */
+static int __devcgroup_check_permission(short type, u32 major, u32 minor,
+				        short access)
+{
+	struct dev_cgroup *dev_cgroup;
+	bool rc;
+
+	rcu_read_lock();
+	dev_cgroup = task_devcgroup(current);
+	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)
+		return -EPERM;
+
+	return 0;
+}
+
+int __devcgroup_inode_permission(struct inode *inode, int mask)
+{
+	short type, access = 0;
+
+	if (S_ISBLK(inode->i_mode))
+		type = DEV_BLOCK;
+	if (S_ISCHR(inode->i_mode))
+		type = DEV_CHAR;
+	if (mask & MAY_WRITE)
+		access |= ACC_WRITE;
+	if (mask & MAY_READ)
+		access |= ACC_READ;
+
+	return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
+			access);
+}
+EXPORT_SYMBOL(__devcgroup_inode_permission);
+
+int devcgroup_inode_mknod(int mode, dev_t dev)
+{
+	short type;
+
+	if (!S_ISBLK(mode) && !S_ISCHR(mode))
+		return 0;
+
+	if (S_ISBLK(mode))
+		type = DEV_BLOCK;
+	else
+		type = DEV_CHAR;
+
+	return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
+			ACC_MKNOD);
+
+}