CRED: Wrap task credential accesses in the x86 arch

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: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: James Morris <jmorris@namei.org>

arch/x86/mm/fault.c

@@ -393,7 +393,7 @@ static void show_fault_oops(struct pt_regs *regs, unsigned long error_code,
 		if (pte && pte_present(*pte) && !pte_exec(*pte))
 			printk(KERN_CRIT "kernel tried to execute "
 				"NX-protected page - exploit attempt? "
-				"(uid: %d)\n", current->uid);
+				"(uid: %d)\n", current_uid());
 	}
 #endif