CRED: Wrap task credential accesses in the filesystem subsystem

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>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/fs/quota.c b/fs/quota.c
index 7f4386e..b7fe44e 100644
--- a/fs/quota.c
+++ b/fs/quota.c
@@ -79,7 +79,7 @@
 
 	/* Check privileges */
 	if (cmd == Q_GETQUOTA) {
-		if (((type == USRQUOTA && current->euid != id) ||
+		if (((type == USRQUOTA && current_euid() != id) ||
 		     (type == GRPQUOTA && !in_egroup_p(id))) &&
 		    !capable(CAP_SYS_ADMIN))
 			return -EPERM;
@@ -130,7 +130,7 @@
 
 	/* Check privileges */
 	if (cmd == Q_XGETQUOTA) {
-		if (((type == XQM_USRQUOTA && current->euid != id) ||
+		if (((type == XQM_USRQUOTA && current_euid() != id) ||
 		     (type == XQM_GRPQUOTA && !in_egroup_p(id))) &&
 		     !capable(CAP_SYS_ADMIN))
 			return -EPERM;