}
/**
- * 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
- * @behavior: behavior of the 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 bool may_access(struct dev_cgroup *dev_cgroup,
- struct dev_exception_item *refex,
- enum devcg_behavior behavior)
+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;
+}
+
+/**
+ * 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) {
- /* the exception will deny access to certain devices */
+ /*
+ * new exception in the child doesn't matter, only
+ * adding extra restrictions
+ */
return true;
} else {
- /* the exception will allow access to certain devices */
+ /*
+ * 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)
- /*
- * a new exception allowing access shouldn't
- * match an parent's exception
- */
return false;
return true;
}
} else {
- /* only behavior == DEVCG_DEFAULT_DENY allowed here */
+ /*
+ * 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;
if (!parent)
return 1;
- return may_access(parent, ex, childcg->behavior);
+ 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(css_parent(&childcg->css));
+
+ 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);
}
/**
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;
}
+
+ if (!parent_has_perm(devcgroup, &ex))
+ return -EPERM;
rc = dev_exception_add(devcgroup, &ex);
break;
case DEVCG_DENY:
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, dev_cgroup->behavior);
+ 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)
projects / linux-beck.git / commitdiff