userns: limit the maximum depth of user_namespace->parent chain

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / kernel / user_namespace.c

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index d8c30db06c5b75456098fe2f1a26785e9a9110ee..9064b919a4066fe9fca676581479e9162de56717 100644 (file)
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -62,6 +62,9 @@ int create_user_ns(struct cred *new)
        kgid_t group = new->egid;
        int ret;
 
+       if (parent_ns->level > 32)
+               return -EUSERS;
+
        /*
         * Verify that we can not violate the policy of which files
         * may be accessed that is specified by the root directory,
@@ -92,6 +95,7 @@ int create_user_ns(struct cred *new)
        atomic_set(&ns->count, 1);
        /* Leave the new->user_ns reference with the new user namespace. */
        ns->parent = parent_ns;
+       ns->level = parent_ns->level + 1;
        ns->owner = owner;
        ns->group = group;
 
@@ -105,16 +109,21 @@ int create_user_ns(struct cred *new)
 int unshare_userns(unsigned long unshare_flags, struct cred **new_cred)
 {
        struct cred *cred;
+       int err = -ENOMEM;
 
        if (!(unshare_flags & CLONE_NEWUSER))
                return 0;
 
        cred = prepare_creds();
-       if (!cred)
-               return -ENOMEM;
+       if (cred) {
+               err = create_user_ns(cred);
+               if (err)
+                       put_cred(cred);
+               else
+                       *new_cred = cred;
+       }
 
-       *new_cred = cred;
-       return create_user_ns(cred);
+       return err;
 }
 
 void free_user_ns(struct user_namespace *ns)