CRED: Introduce credential access wrappers

The patches that are intended to introduce copy-on-write credentials for 2.6.28
require abstraction of access to some fields of the task structure,
particularly for the case of one task accessing another's credentials where RCU
will have to be observed.

Introduced here are trivial no-op versions of the desired accessors for current
and other tasks so that other subsystems can start to be converted over more
easily.

Wrappers are introduced into a new header (linux/cred.h) for UID/GID,
EUID/EGID, SUID/SGID, FSUID/FSGID, cap_effective and current's subscribed
user_struct. These wrappers are macros because the ordering between header
files mitigates against making them inline functions.

linux/cred.h is #included from linux/sched.h.

Further, XFS is modified such that it no longer defines and uses parameterised
versions of current_fs[ug]id(), thus getting rid of the namespace collision
otherwise incurred.

Signed-off-by: David Howells <[e-mail]>
Signed-off-by: James Morris <[e-mail]>

fs/xfs/linux-2.6/xfs_linux.h

···
 
 #define current_cpu()		(raw_smp_processor_id())
 #define current_pid()		(current->pid)
-#define current_fsuid(cred)	(current->fsuid)
-#define current_fsgid(cred)	(current->fsgid)
 #define current_test_flags(f)	(current->flags & (f))
 #define current_set_flags_nested(sp, f)		\
 		(*(sp) = current->flags, current->flags |= (f))

fs/xfs/xfs_inode.c

···
 	ip->i_d.di_onlink = 0;
 	ip->i_d.di_nlink = nlink;
 	ASSERT(ip->i_d.di_nlink == nlink);
-	ip->i_d.di_uid = current_fsuid(cr);
-	ip->i_d.di_gid = current_fsgid(cr);
+	ip->i_d.di_uid = current_fsuid();
+	ip->i_d.di_gid = current_fsgid();
 	ip->i_d.di_projid = prid;
 	memset(&(ip->i_d.di_pad[0]), 0, sizeof(ip->i_d.di_pad));
 

fs/xfs/xfs_vnodeops.c

···
 	xfs_ilock(ip, lock_flags);
 
 	/* boolean: are we the file owner? */
-	file_owner = (current_fsuid(credp) == ip->i_d.di_uid);
+	file_owner = (current_fsuid() == ip->i_d.di_uid);
 
 	/*
 	 * Change various properties of a file.
···
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
 	error = XFS_QM_DQVOPALLOC(mp, dp,
-			current_fsuid(credp), current_fsgid(credp), prid,
+			current_fsuid(), current_fsgid(), prid,
 			XFS_QMOPT_QUOTALL|XFS_QMOPT_INHERIT, &udqp, &gdqp);
 	if (error)
 		goto std_return;
···
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
 	error = XFS_QM_DQVOPALLOC(mp, dp,
-			current_fsuid(credp), current_fsgid(credp), prid,
+			current_fsuid(), current_fsgid(), prid,
 			XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT, &udqp, &gdqp);
 	if (error)
 		goto std_return;
···
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
 	error = XFS_QM_DQVOPALLOC(mp, dp,
-			current_fsuid(credp), current_fsgid(credp), prid,
+			current_fsuid(), current_fsgid(), prid,
 			XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT, &udqp, &gdqp);
 	if (error)
 		goto std_return;

include/linux/cred.h

···
+/* Credentials management
+ *
+ * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([e-mail])
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#ifndef _LINUX_CRED_H
+#define _LINUX_CRED_H
+
+#define get_current_user()	(get_uid(current->user))
+
+#define task_uid(task)		((task)->uid)
+#define task_gid(task)		((task)->gid)
+#define task_euid(task)		((task)->euid)
+#define task_egid(task)		((task)->egid)
+
+#define current_uid()		(current->uid)
+#define current_gid()		(current->gid)
+#define current_euid()		(current->euid)
+#define current_egid()		(current->egid)
+#define current_suid()		(current->suid)
+#define current_sgid()		(current->sgid)
+#define current_fsuid()		(current->fsuid)
+#define current_fsgid()		(current->fsgid)
+#define current_cap()		(current->cap_effective)
+
+#define current_uid_gid(_uid, _gid)		\
+do {						\
+	*(_uid) = current->uid;			\
+	*(_gid) = current->gid;			\
+} while(0)
+
+#define current_euid_egid(_uid, _gid)		\
+do {						\
+	*(_uid) = current->euid;		\
+	*(_gid) = current->egid;		\
+} while(0)
+
+#define current_fsuid_fsgid(_uid, _gid)		\
+do {						\
+	*(_uid) = current->fsuid;		\
+	*(_gid) = current->fsgid;		\
+} while(0)
+
+#endif /* _LINUX_CRED_H */

include/linux/sched.h

···
 #include <linux/task_io_accounting.h>
 #include <linux/kobject.h>
 #include <linux/latencytop.h>
+#include <linux/cred.h>
 
 #include <asm/processor.h>