userns,pidns: Verify the userns for new pid namespaces
It is pointless and confusing to allow a pid namespace hierarchy and
the user namespace hierarchy to get out of sync. The owner of a child
pid namespace should be the owner of the parent pid namespace or
a descendant of the owner of the parent pid namespace.
Otherwise it is possible to construct scenarios where a process has a
capability over a parent pid namespace but does not have the
capability over a child pid namespace. Which confusingly makes
permission checks non-transitive.
It requires use of setns into a pid namespace (but not into a user
namespace) to create such a scenario.
Add the function in_userns to help in making this determination.
v2: Optimized in_userns by using level as suggested
by: Kirill Tkhai <ktkhai@virtuozzo.com>
Ref: 49f4d8b93ccf ("pidns: Capture the user namespace and filter ns_last_pid")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 2f735cb..c490f1e 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -986,17 +986,21 @@
}
/*
- * Returns true if @ns is the same namespace as or a descendant of
- * @target_ns.
+ * Returns true if @child is the same namespace or a descendant of
+ * @ancestor.
*/
+bool in_userns(const struct user_namespace *ancestor,
+ const struct user_namespace *child)
+{
+ const struct user_namespace *ns;
+ for (ns = child; ns->level > ancestor->level; ns = ns->parent)
+ ;
+ return (ns == ancestor);
+}
+
bool current_in_userns(const struct user_namespace *target_ns)
{
- struct user_namespace *ns;
- for (ns = current_user_ns(); ns; ns = ns->parent) {
- if (ns == target_ns)
- return true;
- }
- return false;
+ return in_userns(target_ns, current_user_ns());
}
static inline struct user_namespace *to_user_ns(struct ns_common *ns)