CRED: Wrap task credential accesses in the CIFS filesystem

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: Steve French <sfrench@samba.org>
Cc: linux-cifs-client@lists.samba.org
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/fs/cifs/ioctl.c b/fs/cifs/ioctl.c
index 0088a5b..f946506 100644
--- a/fs/cifs/ioctl.c
+++ b/fs/cifs/ioctl.c
@@ -65,7 +65,7 @@
 	switch (command) {
 		case CIFS_IOC_CHECKUMOUNT:
 			cFYI(1, ("User unmount attempted"));
-			if (cifs_sb->mnt_uid == current->uid)
+			if (cifs_sb->mnt_uid == current_uid())
 				rc = 0;
 			else {
 				rc = -EACCES;