musl - No fallback to /bin/sh in execvp

Follow @Openwall on Twitter for new release announcements and other news

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <3a04ed7d2f8748a79941a3676658fc25@sap.com>
Date: Fri, 9 Mar 2018 12:23:06 +0000
From: "Siebenborn, Axel" <axel.siebenborn@....com>
To: "musl@...ts.openwall.com" <musl@...ts.openwall.com>
Subject: No fallback to /bin/sh in execvp

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,

Kind regards,
Axel

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.