CRED: Wrap task credential accesses in the GFS2 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: Steven Whitehouse <swhiteho@redhat.com>
Cc: cluster-devel@redhat.com
Signed-off-by: James Morris <jmorris@namei.org>

fs/gfs2/inode.c

@@ -705,18 +705,18 @@ static void munge_mode_uid_gid(struct gfs2_inode *dip, unsigned int *mode,
 	    (dip->i_inode.i_mode & S_ISUID) && dip->i_inode.i_uid) {
 		if (S_ISDIR(*mode))
 			*mode |= S_ISUID;
-		else if (dip->i_inode.i_uid != current->fsuid)
+		else if (dip->i_inode.i_uid != current_fsuid())
 			*mode &= ~07111;
 		*uid = dip->i_inode.i_uid;
 	} else
-		*uid = current->fsuid;
+		*uid = current_fsuid();
 
 	if (dip->i_inode.i_mode & S_ISGID) {
 		if (S_ISDIR(*mode))
 			*mode |= S_ISGID;
 		*gid = dip->i_inode.i_gid;
 	} else
-		*gid = current->fsgid;
+		*gid = current_fsgid();
 }
 
 static int alloc_dinode(struct gfs2_inode *dip, u64 *no_addr, u64 *generation)
@@ -1124,8 +1124,8 @@ int gfs2_unlink_ok(struct gfs2_inode *dip, const struct qstr *name,
 		return -EPERM;
 
 	if ((dip->i_inode.i_mode & S_ISVTX) &&
-	    dip->i_inode.i_uid != current->fsuid &&
-	    ip->i_inode.i_uid != current->fsuid && !capable(CAP_FOWNER))
+	    dip->i_inode.i_uid != current_fsuid() &&
+	    ip->i_inode.i_uid != current_fsuid() && !capable(CAP_FOWNER))
 		return -EPERM;
 
 	if (IS_APPEND(&dip->i_inode))