CRED: Detach the credentials from task_struct

Detach the credentials from task_struct, duplicating them in copy_process()
and releasing them in __put_task_struct().

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 96 insertions, 0 deletions

diff --git a/kernel/cred.c b/kernel/cred.c
new file mode 100644
index 000000000000..833244a7cb05
--- /dev/null
+++ b/kernel/cred.c
@@ -0,0 +1,96 @@
+/* Task credentials management
+ *
+ * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+#include <linux/module.h>
+#include <linux/cred.h>
+#include <linux/sched.h>
+#include <linux/key.h>
+#include <linux/keyctl.h>
+#include <linux/init_task.h>
+#include <linux/security.h>
+
+/*
+ * The initial credentials for the initial task
+ */
+struct cred init_cred = {
+        .usage                  = ATOMIC_INIT(3),
+        .securebits             = SECUREBITS_DEFAULT,
+        .cap_inheritable        = CAP_INIT_INH_SET,
+        .cap_permitted          = CAP_FULL_SET,
+        .cap_effective          = CAP_INIT_EFF_SET,
+        .cap_bset               = CAP_INIT_BSET,
+        .user                   = INIT_USER,
+        .group_info             = &init_groups,
+};
+
+/*
+ * The RCU callback to actually dispose of a set of credentials
+ */
+static void put_cred_rcu(struct rcu_head *rcu)
+{
+        struct cred *cred = container_of(rcu, struct cred, rcu);
+
+        BUG_ON(atomic_read(&cred->usage) != 0);
+
+        key_put(cred->thread_keyring);
+        key_put(cred->request_key_auth);
+        put_group_info(cred->group_info);
+        free_uid(cred->user);
+        security_cred_free(cred);
+        kfree(cred);
+}
+
+/**
+ * __put_cred - Destroy a set of credentials
+ * @sec: The record to release
+ *
+ * Destroy a set of credentials on which no references remain.
+ */
+void __put_cred(struct cred *cred)
+{
+        call_rcu(&cred->rcu, put_cred_rcu);
+}
+EXPORT_SYMBOL(__put_cred);
+
+/*
+ * Copy credentials for the new process created by fork()
+ */
+int copy_creds(struct task_struct *p, unsigned long clone_flags)
+{
+        struct cred *pcred;
+        int ret;
+
+        pcred = kmemdup(p->cred, sizeof(*p->cred), GFP_KERNEL);
+        if (!pcred)
+                return -ENOMEM;
+
+#ifdef CONFIG_SECURITY
+        pcred->security = NULL;
+#endif
+
+        ret = security_cred_alloc(pcred);
+        if (ret < 0) {
+                kfree(pcred);
+                return ret;
+        }
+
+        atomic_set(&pcred->usage, 1);
+        get_group_info(pcred->group_info);
+        get_uid(pcred->user);
+        key_get(pcred->thread_keyring);
+        key_get(pcred->request_key_auth);
+
+        atomic_inc(&pcred->user->processes);
+
+        /* RCU assignment is unneeded here as no-one can have accessed this
+         * pointer yet, barring us */
+        p->cred = pcred;
+        return 0;
+}