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Date: Tue, 3 Sep 1996 05:30:00 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199609021930.FAA32641@godzilla.zeta.org.au>
To: jkh@time.cdrom.com, wollman@lcs.mit.edu
Subject: Re: Anyone mind if I remove the following braindamage from test(1)?
Cc: bde@zeta.org.au, freebsd-current@FreeBSD.org,
        joerg_wunsch@uriah.heep.sax.de
Sender: owner-current@FreeBSD.org
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>Use:

>	[ -d "$foo" ]

>instead of

>	[ -d $foo ]

>.  This will ensure that two arguments get passed to the `-d'
>primitive, even if $foo is not defined.

This only works right on POSIX systems.  Under FreeBSD, "" is
an alias for ".", so if $foo is empty,

	[ -d "$foo" ]

almost always succeeds.

There is also a bug in bash's builtin test.  On freefall:

$bash test -d ''; echo $?
1
$bash /bin/test -d ''; echo $?
0

I have used this fix for a year or three.  I fixed empty pathnames in
many programs but there are still several standard programs with
harmless bugs in this area.  Tar apparently strips one too many
slash from "/", and there's a rare case in gzip where it does a
harmless stat() of "".

Bruce

diff -c2 src/sys/kern/vfs_lookup.c~ src/sys/kern/vfs_lookup.c
*** src/sys/kern/vfs_lookup.c~	Thu Jan  4 17:07:54 1996
--- src/sys/kern/vfs_lookup.c	Wed Mar  6 17:58:20 1996
***************
*** 53,56 ****
--- 53,57 ----
  #include <sys/filedesc.h>
  #include <sys/proc.h>
+ #include <sys/syslog.h>
  
  #ifdef KTRACE
***************
*** 113,116 ****
--- 114,129 ----
  		error = copyinstr(ndp->ni_dirp, cnp->cn_pnbuf,
  			    MAXPATHLEN, (u_int *)&ndp->ni_pathlen);
+ 
+ 	/*
+ 	 * Don't allow empty pathname.
+ 	 * Log the error until we find the standard utilities that cause it.
+ 	 */
+ 	if (!error && *cnp->cn_pnbuf == '\0') {
+ 		log(LOG_ERR,
+ 		    "pid %d (%s) called namei with an empty pathname\n",
+ 		    cnp->cn_proc->p_pid, cnp->cn_proc->p_comm);
+ 		error = ENOENT;
+ 	}
+ 
  	if (error) {
  		free(cnp->cn_pnbuf, M_NAMEI);