2 files changed, 58 insertions, 0 deletions

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index cc4f45361dbb..8178156711f9 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -36,6 +36,9 @@ static inline void put_user_ns(struct user_namespace *ns)
                 kref_put(&ns->kref, free_user_ns);
 }
 
+uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid);
+gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid);
+
 #else
 
 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
@@ -52,6 +55,17 @@ static inline void put_user_ns(struct user_namespace *ns)
 {
 }
 
+static inline uid_t user_ns_map_uid(struct user_namespace *to,
+        const struct cred *cred, uid_t uid)
+{
+        return uid;
+}
+static inline gid_t user_ns_map_gid(struct user_namespace *to,
+        const struct cred *cred, gid_t gid)
+{
+        return gid;
+}
+
 #endif
 
 #endif /* _LINUX_USER_H */
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index b2d70d38dff4..25915832291a 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -9,6 +9,7 @@
 #include <linux/nsproxy.h>
 #include <linux/slab.h>
 #include <linux/user_namespace.h>
+#include <linux/highuid.h>
 #include <linux/cred.h>
 
 /*
@@ -82,3 +83,46 @@ void free_user_ns(struct kref *kref)
         schedule_work(&ns->destroyer);
 }
 EXPORT_SYMBOL(free_user_ns);
+
+uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid)
+{
+        struct user_namespace *tmp;
+
+        if (likely(to == cred->user->user_ns))
+                return uid;
+
+
+        /* Is cred->user the creator of the target user_ns
+         * or the creator of one of it's parents?
+         */
+        for ( tmp = to; tmp != &init_user_ns;
+              tmp = tmp->creator->user_ns ) {
+                if (cred->user == tmp->creator) {
+                        return (uid_t)0;
+                }
+        }
+
+        /* No useful relationship so no mapping */
+        return overflowuid;
+}
+
+gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid)
+{
+        struct user_namespace *tmp;
+
+        if (likely(to == cred->user->user_ns))
+                return gid;
+
+        /* Is cred->user the creator of the target user_ns
+         * or the creator of one of it's parents?
+         */
+        for ( tmp = to; tmp != &init_user_ns;
+              tmp = tmp->creator->user_ns ) {
+                if (cred->user == tmp->creator) {
+                        return (gid_t)0;
+                }
+        }
+
+        /* No useful relationship so no mapping */
+        return overflowgid;
+}