CRED: Wrap task credential accesses in the NFS daemon

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: J. Bruce Fields <bfields@fieldses.org>
Cc: Neil Brown <neilb@suse.de>
Cc: linux-nfs@vger.kernel.org
Signed-off-by: James Morris <jmorris@namei.org>

fs/nfsd/vfs.c

@@ -1169,7 +1169,7 @@ nfsd_create_setattr(struct svc_rqst *rqstp, struct svc_fh *resfhp,
 	 * send along the gid on create when it tries to implement
 	 * setgid directories via NFS:
 	 */
-	if (current->fsuid != 0)
+	if (current_fsuid() != 0)
 		iap->ia_valid &= ~(ATTR_UID|ATTR_GID);
 	if (iap->ia_valid)
 		return nfsd_setattr(rqstp, resfhp, iap, 0, (time_t)0);
@@ -2004,7 +2004,7 @@ nfsd_permission(struct svc_rqst *rqstp, struct svc_export *exp,
 		IS_APPEND(inode)?	" append" : "",
 		__mnt_is_readonly(exp->ex_path.mnt)?	" ro" : "");
 	dprintk("      owner %d/%d user %d/%d\n",
-		inode->i_uid, inode->i_gid, current->fsuid, current->fsgid);
+		inode->i_uid, inode->i_gid, current_fsuid(), current_fsgid());
 #endif
 
 	/* Normally we reject any write/sattr etc access on a read-only file
@@ -2047,7 +2047,7 @@ nfsd_permission(struct svc_rqst *rqstp, struct svc_export *exp,
 	 * with NFSv3.
 	 */
 	if ((acc & NFSD_MAY_OWNER_OVERRIDE) &&
-	    inode->i_uid == current->fsuid)
+	    inode->i_uid == current_fsuid())
 		return 0;
 
 	/* This assumes  NFSD_MAY_{READ,WRITE,EXEC} == MAY_{READ,WRITE,EXEC} */