From owner-freebsd-current@freebsd.org  Wed Nov  2 19:24:47 2016
Return-Path: <owner-freebsd-current@freebsd.org>
Delivered-To: freebsd-current@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id 315D2C2C997
 for <freebsd-current@mailman.ysv.freebsd.org>;
 Wed,  2 Nov 2016 19:24:47 +0000 (UTC)
 (envelope-from vangyzen@FreeBSD.org)
Received: from mailman.ysv.freebsd.org (unknown [127.0.1.3])
 by mx1.freebsd.org (Postfix) with ESMTP id A62B01063
 for <freebsd-current@freebsd.org>; Wed,  2 Nov 2016 19:24:46 +0000 (UTC)
 (envelope-from vangyzen@FreeBSD.org)
Received: by mailman.ysv.freebsd.org (Postfix)
 id A120DC2C996; Wed,  2 Nov 2016 19:24:46 +0000 (UTC)
Delivered-To: current@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id A0A8FC2C995
 for <current@mailman.ysv.freebsd.org>; Wed,  2 Nov 2016 19:24:46 +0000 (UTC)
 (envelope-from vangyzen@FreeBSD.org)
Received: from smtp.vangyzen.net (hotblack.vangyzen.net
 [IPv6:2607:fc50:1000:7400:216:3eff:fe72:314f])
 by mx1.freebsd.org (Postfix) with ESMTP id 71C0C105E
 for <current@freebsd.org>; Wed,  2 Nov 2016 19:24:46 +0000 (UTC)
 (envelope-from vangyzen@FreeBSD.org)
Received: from sweettea.beer.town (unknown [76.164.8.130])
 by smtp.vangyzen.net (Postfix) with ESMTPSA id BD4DE5648E
 for <current@freebsd.org>; Wed,  2 Nov 2016 14:24:45 -0500 (CDT)
To: "current@freebsd.org" <current@freebsd.org>
From: Eric van Gyzen <vangyzen@FreeBSD.org>
Subject: copyinstr and ENAMETOOLONG
Message-ID: <236b8c7c-a12e-0872-f3cb-03f99bb5fcc5@FreeBSD.org>
Date: Wed, 2 Nov 2016 14:24:43 -0500
User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:45.0) Gecko/20100101
 Thunderbird/45.3.0
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.23
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
 <freebsd-current.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/freebsd-current>, 
 <mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current/>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/freebsd-current>, 
 <mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 02 Nov 2016 19:24:47 -0000

Does copyinstr guarantee that it has filled the output buffer when it
returns ENAMETOOLONG?  I usually try to answer my own questions, but I
don't speak many dialects of assembly.  :)

I ask because I'd like to make the following change, and I'd like to
know whether I should zero the buffer before calling copyinstr to ensure
that I don't set the thread's name to the garbage that was on the stack.

Eric

Index: kern_thr.c
===================================================================
--- kern_thr.c	(revision 308217)
+++ kern_thr.c	(working copy)
@@ -580,8 +580,13 @@ sys_thr_set_name(struct thread *td, struct thr_set
 	if (uap->name != NULL) {
 		error = copyinstr(uap->name, name, sizeof(name),
 			NULL);
-		if (error)
-			return (error);
+		if (error) {
+			if (error == ENAMETOOLONG) {
+				name[sizeof(name) - 1] = '\0';
+			} else {
+				return (error);
+			}
+		}
 	}
 	p = td->td_proc;
 	ttd = tdfind((lwpid_t)uap->id, p->p_pid);