CRED: Wrap task credential accesses in the core kernel

Wrap access to task credentials so that they can be separated more easily from
the task_struct during the introduction of COW creds.

Change most current->(|e|s|fs)[ug]id to current_(|e|s|fs)[ug]id().

Change some task->e?[ug]id to task_e?[ug]id().  In some places it makes more
sense to use RCU directly rather than a convenient wrapper; these will be
addressed by later patches.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-audit@redhat.com
Cc: containers@lists.linux-foundation.org
Cc: linux-mm@kvack.org
Signed-off-by: James Morris <jmorris@namei.org>

mm/mempolicy.c

@@ -1115,6 +1115,7 @@ asmlinkage long sys_migrate_pages(pid_t pid, unsigned long maxnode,
 	nodemask_t old;
 	nodemask_t new;
 	nodemask_t task_nodes;
+	uid_t uid, euid;
 	int err;
 
 	err = get_nodes(&old, old_nodes, maxnode);
@@ -1144,8 +1145,10 @@ asmlinkage long sys_migrate_pages(pid_t pid, unsigned long maxnode,
 	 * capabilities, superuser privileges or the same
 	 * userid as the target process.
 	 */
-	if ((current->euid != task->suid) && (current->euid != task->uid) &&
-	    (current->uid != task->suid) && (current->uid != task->uid) &&
+	uid = current_uid();
+	euid = current_euid();
+	if (euid != task->suid && euid != task->uid &&
+	    uid  != task->suid && uid  != task->uid &&
 	    !capable(CAP_SYS_NICE)) {
 		err = -EPERM;
 		goto out;