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Re: Built-in "test -x" fails for root on FreeBSD


From: Eric Blake
Subject: Re: Built-in "test -x" fails for root on FreeBSD
Date: Mon, 29 Mar 2010 08:01:46 -0600
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On 03/26/2010 11:47 PM, Johan Hattne wrote:
> Description:
>   The bash built-in test command fails to correctly report executable
>   status for non-executable files when run by root on FreeBSD.

Not a bug.  POSIX states for test -x:

True if pathname resolves to an existing directory entry for a file for
which permission to execute the file (or search it, if it is a
directory) will be granted, as defined in File Read, Write, and Creation.
http://www.opengroup.org/onlinepubs/9699919799/utilities/test.html

It further states:

If a process has appropriate privileges:
    * If read, write, or directory search permission is requested,
access shall be granted.
    * If execute permission is requested, access shall be granted if
execute permission is granted to at least one user by the file
permission bits or by an alternate access control mechanism; otherwise,
access shall be denied.

http://www.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_04

It also states for faccessat (eaccess is a non-portable interface
comparable to the standardized faccessat):

If any access permissions are checked, each shall be checked
individually, as described in XBD File Access Permissions , except that
where that description refers to execute permission for a process with
appropriate privileges, an implementation may indicate success for X_OK
even if execute permission is not granted to any user.
http://www.opengroup.org/onlinepubs/9699919799/functions/access.html

Therefore, it is perfectly acceptable for the root user to claim that a
file is executable, as reported by eaccess, even if none of the file
permission bits grant such permission.

>  #if defined (HAVE_EACCESS)        /* FreeBSD */
> -  return (eaccess (path, mode));
> +  if (stat (path, &s) != 0)
> +    return (-1);
> +  ret = eaccess (path, mode);
> +  if (mode == X_OK && ret == 0 && !S_ISDIR(s.st_mode) && geteuid() == 0)
> +    return ((s.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH)) == 0 ? -1 : 0);
> +  return (ret);

This patch fails to take into account ACLs, which is one of the reasons
that faccessat was standardized.

-- 
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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