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>

3 files changed, 103 insertions, 19 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index 9a3ec66a9d84..5a6a612c302d 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -9,7 +9,7 @@ obj-y     = sched.o fork.o exec_domain.o panic.o printk.o \
             rcupdate.o extable.o params.o posix-timers.o \
             kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
             hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
-            notifier.o ksysfs.o pm_qos_params.o sched_clock.o
+            notifier.o ksysfs.o pm_qos_params.o sched_clock.o cred.o
 
 CFLAGS_REMOVE_sched.o = -mno-spe
 
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;
+}
diff --git a/kernel/fork.c b/kernel/fork.c
index 81fdc7733908..c932e283ddfc 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -146,9 +146,7 @@ void __put_task_struct(struct task_struct *tsk)
         WARN_ON(atomic_read(&tsk->usage));
         WARN_ON(tsk == current);
 
-        security_task_free(tsk);
-        free_uid(tsk->__temp_cred.user);
-        put_group_info(tsk->__temp_cred.group_info);
+        put_cred(tsk->cred);
         delayacct_tsk_free(tsk);
 
         if (!profile_handoff_task(tsk))
@@ -969,7 +967,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
 #endif
-        p->cred = &p->__temp_cred;
         retval = -EAGAIN;
         if (atomic_read(&p->cred->user->processes) >=
                         p->signal->rlim[RLIMIT_NPROC].rlim_cur) {
@@ -978,9 +975,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
                         goto bad_fork_free;
         }
 
-        atomic_inc(&p->cred->user->__count);
-        atomic_inc(&p->cred->user->processes);
-        get_group_info(p->cred->group_info);
+        retval = copy_creds(p, clone_flags);
+        if (retval < 0)
+                goto bad_fork_free;
 
         /*
          * If multiple threads are within copy_process(), then this check
@@ -1035,9 +1032,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         do_posix_clock_monotonic_gettime(&p->start_time);
         p->real_start_time = p->start_time;
         monotonic_to_bootbased(&p->real_start_time);
-#ifdef CONFIG_SECURITY
-        p->cred->security = NULL;
-#endif
         p->io_context = NULL;
         p->audit_context = NULL;
         cgroup_fork(p);
@@ -1082,10 +1076,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         /* Perform scheduler related setup. Assign this task to a CPU. */
         sched_fork(p, clone_flags);
 
-        if ((retval = security_task_alloc(p)))
-                goto bad_fork_cleanup_policy;
         if ((retval = audit_alloc(p)))
-                goto bad_fork_cleanup_security;
+                goto bad_fork_cleanup_policy;
         /* copy all the process information */
         if ((retval = copy_semundo(clone_flags, p)))
                 goto bad_fork_cleanup_audit;
@@ -1284,8 +1276,6 @@ bad_fork_cleanup_semundo:
         exit_sem(p);
 bad_fork_cleanup_audit:
         audit_free(p);
-bad_fork_cleanup_security:
-        security_task_free(p);
 bad_fork_cleanup_policy:
 #ifdef CONFIG_NUMA
         mpol_put(p->mempolicy);
@@ -1298,9 +1288,7 @@ bad_fork_cleanup_cgroup:
 bad_fork_cleanup_put_domain:
         module_put(task_thread_info(p)->exec_domain->module);
 bad_fork_cleanup_count:
-        put_group_info(p->cred->group_info);
-        atomic_dec(&p->cred->user->processes);
-        free_uid(p->cred->user);
+        put_cred(p->cred);
 bad_fork_free:
         free_task(p);
 fork_out: