From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <pengyu.ut@gmail.com>
Received: from mail-io1-xd2f.google.com (mail-io1-xd2f.google.com
 [IPv6:2607:f8b0:4864:20::d2f])
 by sourceware.org (Postfix) with ESMTPS id 74C87388A43B
 for <libc-help@sourceware.org>; Fri,  9 Apr 2021 16:53:40 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 74C87388A43B
Received: by mail-io1-xd2f.google.com with SMTP id z136so6558318iof.10
 for <libc-help@sourceware.org>; Fri, 09 Apr 2021 09:53:40 -0700 (PDT)
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=1e100.net; s=20161025;
 h=x-gm-message-state:mime-version:from:date:message-id:subject:to;
 bh=SvAJIjXoR1w5M01WAOJRVt8RlMlPcKcrO9jpQQgtVHE=;
 b=lmkhfTfO768kg2awGCC3mbcuNSnxg4zoz81pTudHu5rp2pws7Rjb6t68e9XHdZJrHz
 bUreD0qLKruv8+OIg3XQiJeOMScxy3lOk/WFw7ya9AR70BTOP7o3vv3Zm7h1LHFvqnKT
 2chYhfbREIqUPfM2aKAMYcK+cyGJvpMCLq35fJPJHRm+QriuFYVH13LLsfmRZbJXBA+5
 l8IO1LbUjFG2OPcAptm+hRxTOgw93YmrNz00HZiO5KiynvuJVDsVV5IXxsngfDhuztai
 LJoMPWW0uWszzpfLLvgCLvaUaakyxtD4JtMzNZS44hxf/68AT/Z8hYIc+jofMdldeB7V
 c8sw==
X-Gm-Message-State: AOAM530RFfoUxUo4Vcwc4HTmR2xnFWk8O3RxoXhjVNenALDkKfhFtZWP
 Nl+7FQv5ngk2EccNfbvu/8BYBWfgLeTb4wchSeISHDNN23I=
X-Google-Smtp-Source: ABdhPJzcbwy+NPRjRlsJKg6nvku4WLxlztI9mfhl133VjFhObk+szxHIUoKmzDP4GhO/GLxbzvVEdpVYa/FqMCykaj8=
X-Received: by 2002:a6b:6f14:: with SMTP id k20mr12389280ioc.52.1617987219732; 
 Fri, 09 Apr 2021 09:53:39 -0700 (PDT)
MIME-Version: 1.0
Received: by 2002:a05:6602:349:0:0:0:0 with HTTP; Fri, 9 Apr 2021 09:53:39
 -0700 (PDT)
From: Peng Yu <pengyu.ut@gmail.com>
Date: Fri, 9 Apr 2021 11:53:39 -0500
Message-ID: <CABrM6wkYV4qn0V=7j5FPD8jB9Dn2M+fjQHJHrEpvnqJ4aA_riQ@mail.gmail.com>
Subject: When is it OK to pass NULLs to the 2nd and 3rd args of execve()?
To: libc-help <libc-help@sourceware.org>
Content-Type: text/plain; charset="UTF-8"
X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00, DKIM_SIGNED,
 DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, RCVD_IN_DNSWL_NONE,
 SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2
X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on
 server2.sourceware.org
X-BeenThere: libc-help@sourceware.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Libc-help mailing list <libc-help.sourceware.org>
List-Unsubscribe: <https://sourceware.org/mailman/options/libc-help>,
 <mailto:libc-help-request@sourceware.org?subject=unsubscribe>
List-Archive: <https://sourceware.org/pipermail/libc-help/>
List-Help: <mailto:libc-help-request@sourceware.org?subject=help>
List-Subscribe: <https://sourceware.org/mailman/listinfo/libc-help>,
 <mailto:libc-help-request@sourceware.org?subject=subscribe>
X-List-Received-Date: Fri, 09 Apr 2021 16:53:41 -0000

Hi,

I am wondering when (all possible legitimate cases) it is OK to pass
NULLs to execve's 2nd and 3rd args.

#include <unistd.h>
#include <stdio.h>

int main(int argc, char *argv[]) {
	if(execve(argv[1], NULL, NULL) == -1) {
		perror("execvp()");
		return 1;
	}
	return 0;
}


I tried the above program. It works when it is called with `/bin/sh`.
My guess is that when the program being exec'ed don't use its args and
envs, then then 2nd and 3rd args of execve() can be NULLs. Could
anybody correct me if I am wrong?

-- 
Regards,
Peng