2 files changed, 17 insertions, 1 deletions

diff --git a/kernel/groups.c b/kernel/groups.c
index 02d8a251c476..664411f171b5 100644
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -6,6 +6,7 @@
 #include <linux/slab.h>
 #include <linux/security.h>
 #include <linux/syscalls.h>
+#include <linux/user_namespace.h>
 #include <asm/uaccess.h>
 
 /* init to 2 - one for init_task, one to ensure it is never freed */
@@ -217,7 +218,8 @@ bool may_setgroups(void)
 {
         struct user_namespace *user_ns = current_user_ns();
 
-        return ns_capable(user_ns, CAP_SETGID);
+        return ns_capable(user_ns, CAP_SETGID) &&
+                userns_may_setgroups(user_ns);
 }
 
 /*
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index b99c862a2e3f..27c8dab48c07 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -843,6 +843,20 @@ static bool new_idmap_permitted(const struct file *file,
         return false;
 }
 
+bool userns_may_setgroups(const struct user_namespace *ns)
+{
+        bool allowed;
+
+        mutex_lock(&id_map_mutex);
+        /* It is not safe to use setgroups until a gid mapping in
+         * the user namespace has been established.
+         */
+        allowed = ns->gid_map.nr_extents != 0;
+        mutex_unlock(&id_map_mutex);
+
+        return allowed;
+}
+
 static void *userns_get(struct task_struct *task)
 {
         struct user_namespace *user_ns;