From mboxrd@z Thu Jan  1 00:00:00 1970
X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/12594
Path: news.gmane.org!.POSTED!not-for-mail
From: Rich Felker <dalias@libc.org>
Newsgroups: gmane.linux.lib.musl.general
Subject: Re: No fallback to /bin/sh in execvp
Date: Fri, 9 Mar 2018 12:01:40 -0500
Message-ID: <20180309170140.GQ1436@brightrain.aerifal.cx>
References: <3a04ed7d2f8748a79941a3676658fc25@sap.com>
Reply-To: musl@lists.openwall.com
NNTP-Posting-Host: blaine.gmane.org
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: blaine.gmane.org 1520614795 9881 195.159.176.226 (9 Mar 2018 16:59:55 GMT)
X-Complaints-To: usenet@blaine.gmane.org
NNTP-Posting-Date: Fri, 9 Mar 2018 16:59:55 +0000 (UTC)
User-Agent: Mutt/1.5.21 (2010-09-15)
To: musl@lists.openwall.com
Original-X-From: musl-return-12608-gllmg-musl=m.gmane.org@lists.openwall.com Fri Mar 09 17:59:51 2018
Return-path: <musl-return-12608-gllmg-musl=m.gmane.org@lists.openwall.com>
Envelope-to: gllmg-musl@m.gmane.org
Original-Received: from mother.openwall.net ([195.42.179.200])
	by blaine.gmane.org with smtp (Exim 4.84_2)
	(envelope-from <musl-return-12608-gllmg-musl=m.gmane.org@lists.openwall.com>)
	id 1euLMz-0002RG-Sv
	for gllmg-musl@m.gmane.org; Fri, 09 Mar 2018 17:59:49 +0100
Original-Received: (qmail 18229 invoked by uid 550); 9 Mar 2018 17:01:53 -0000
Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm
Precedence: bulk
List-Post: <mailto:musl@lists.openwall.com>
List-Help: <mailto:musl-help@lists.openwall.com>
List-Unsubscribe: <mailto:musl-unsubscribe@lists.openwall.com>
List-Subscribe: <mailto:musl-subscribe@lists.openwall.com>
List-ID: <musl.lists.openwall.com>
Original-Received: (qmail 18206 invoked from network); 9 Mar 2018 17:01:52 -0000
Content-Disposition: inline
In-Reply-To: <3a04ed7d2f8748a79941a3676658fc25@sap.com>
Original-Sender: Rich Felker <dalias@aerifal.cx>
Xref: news.gmane.org gmane.linux.lib.musl.general:12594
Archived-At: <http://permalink.gmane.org/gmane.linux.lib.musl.general/12594>

On Fri, Mar 09, 2018 at 12:23:06PM +0000, Siebenborn, Axel wrote:
> Hi,
> 
> I encountered a problem with execvp with musl.
> Trying to execute shell scripts without #! fails with ENOEXEC.
> However, according to the standard, execvp should fallback to execute the file using /bin/sh.
> 
> A simple test:
> 
> Create a  script file 'prog'  without '!#' with the following content and make it executable:
> 
> /bin/echo "$@" 
> 
> Compile and run the following c-program:
> 
> #include <unistd.h>
> #include <stdio.h>
> #include <string.h>
> #include <errno.h>
> 
> int main (){
>   int ret;
>   char *cmd[] = { "./prog","Hello", "World", (char *)0 };
>   ret = execvp ("./prog", cmd);
>   int errorNumber = errno;
>   printf("Error code: %d. Error message: %s\n", errorNumber, strerror(errorNumber));
> }
> 
> With musl the execution results in the following error:
> 
> Error code: 8. Error message: Exec format error
> 
> With glibs 'Hello world' is printed.
> 
> Is this a bug, that will be fixed someday or intended behavior for security reasons.
> 
> I think it's a quiet a strange way to execute shell commands. However, some ancient code might rely on this 
> and compatibility wins over sanity,

It's a bug, but one that was considered low priority since real-world
usage is for scripts to start with #!, in which case the kernel
handles invocation. Actually doing what the standard requires here
seems hard since we'd need to allocate storage for the new argv...

Rich