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-rw-r--r--security/device_cgroup.c41
1 files changed, 38 insertions, 3 deletions
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 6b1266dd92bb..9134dbf70d3e 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -463,6 +463,37 @@ static int parent_has_perm(struct dev_cgroup *childcg,
}
/**
+ * 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);
+}
+
+/**
* may_allow_all - checks if it's possible to change the behavior to
* allow based on parent's rules.
* @parent: device cgroup's parent
@@ -697,17 +728,21 @@ 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;
}
+
+ if (!parent_has_perm(devcgroup, &ex))
+ return -EPERM;
rc = dev_exception_add(devcgroup, &ex);
break;
case DEVCG_DENY: