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>
diff --git a/kernel/acct.c b/kernel/acct.c
index f6006a6..d57b7cb 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -530,15 +530,14 @@
 	do_div(elapsed, AHZ);
 	ac.ac_btime = get_seconds() - elapsed;
 	/* we really need to bite the bullet and change layout */
-	ac.ac_uid = current->uid;
-	ac.ac_gid = current->gid;
+	current_uid_gid(&ac.ac_uid, &ac.ac_gid);
 #if ACCT_VERSION==2
 	ac.ac_ahz = AHZ;
 #endif
 #if ACCT_VERSION==1 || ACCT_VERSION==2
 	/* backward-compatible 16 bit fields */
-	ac.ac_uid16 = current->uid;
-	ac.ac_gid16 = current->gid;
+	ac.ac_uid16 = ac.ac_uid;
+	ac.ac_gid16 = ac.ac_gid;
 #endif
 #if ACCT_VERSION==3
 	ac.ac_pid = task_tgid_nr_ns(current, ns);