CRED: Wrap task credential accesses in the devpts 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>
Signed-off-by: James Morris <jmorris@namei.org>

fs/devpts/inode.c

@@ -222,8 +222,8 @@ int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty)
 		return -ENOMEM;
 
 	inode->i_ino = number+2;
-	inode->i_uid = config.setuid ? config.uid : current->fsuid;
-	inode->i_gid = config.setgid ? config.gid : current->fsgid;
+	inode->i_uid = config.setuid ? config.uid : current_fsuid();
+	inode->i_gid = config.setgid ? config.gid : current_fsgid();
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 	init_special_inode(inode, S_IFCHR|config.mode, device);
 	inode->i_private = tty;