[RFC PATCH 21/30] user namespace: Add function that checks if the UID map is defined

[<krzysztof.struczynski@huawei.com>]

From: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>

Add function that checks if the UID map is defined. It will be used by
ima to check if ID remapping in subject-based rules is necessary.

Signed-off-by: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>
---
 include/linux/user_namespace.h |  6 ++++++
 kernel/user_namespace.c        | 11 +++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index d9759c54fead..bcb21c41c910 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -138,6 +138,7 @@ extern bool in_userns(const struct user_namespace *ancestor,
 		       const struct user_namespace *child);
 extern bool current_in_userns(const struct user_namespace *target_ns);
 struct ns_common *ns_get_owner(struct ns_common *ns);
+extern bool userns_set_uidmap(const struct user_namespace *ns);
 #else
 
 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
@@ -182,6 +183,11 @@ static inline struct ns_common *ns_get_owner(struct ns_common *ns)
 {
 	return ERR_PTR(-EPERM);
 }
+
+static inline bool userns_set_uidmap(const struct user_namespace *ns)
+{
+	return true;
+}
 #endif
 
 #endif /* _LINUX_USER_H */
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 87804e0371fe..e38f9f11a589 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -1232,6 +1232,17 @@ bool current_in_userns(const struct user_namespace *target_ns)
 }
 EXPORT_SYMBOL(current_in_userns);
 
+bool userns_set_uidmap(const struct user_namespace *ns)
+{
+	bool mapping_defined;
+
+	mutex_lock(&userns_state_mutex);
+	mapping_defined = ns->uid_map.nr_extents != 0;
+	mutex_unlock(&userns_state_mutex);
+
+	return mapping_defined;
+}
+
 static inline struct user_namespace *to_user_ns(struct ns_common *ns)
 {
 	return container_of(ns, struct user_namespace, ns);
-- 
2.20.1