openat: allow return of fd 0

Partially reverts patch fc33350 from 2009-09-02.

* modules/chdir-long (Depends-on): Relax openat-safer to openat.
* modules/save-cwd (Depends-on): Replace fcntl-safer with
unistd-safer.
* lib/chdir-long.c (includes): Replace "fcntl--.h" with
<fcntl.h>; this module does not leak fds.
* lib/openat.c (includes): Do not use "fcntl_safer"; plain openat
must be allowed to return 0, leaving openat_safer to add the
safety.
(openat_permissive): Avoid writing to just-opened fd 2 if
restoring the current directory fails.
* lib/openat-die.c (openat_restore_fail): Add comment.
* lib/save-cwd.c (includes): Make "fcntl--.h" conditional.
(save_cwd): Guarantee safe fd, but without use of open_safer.
* tests/test-openat.c: New test.
* modules/openat-tests (Files, Makefile.am): Distribute and build
new file.

Signed-off-by: Eric Blake <ebb9@byu.net>

1 files changed, 11 insertions, 3 deletions

diff --git a/lib/save-cwd.c b/lib/save-cwd.c
index e158e8b6b2..7c2eb6d94f 100644
--- a/lib/save-cwd.c
+++ b/lib/save-cwd.c
@@ -1,6 +1,6 @@
 /* save-cwd.c -- Save and restore current working directory.
 
-   Copyright (C) 1995, 1997, 1998, 2003, 2004, 2005, 2006 Free
+   Copyright (C) 1995, 1997, 1998, 2003, 2004, 2005, 2006, 2009 Free
    Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
@@ -23,15 +23,21 @@
 #include "save-cwd.h"
 
 #include <errno.h>
+#include <fcntl.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <unistd.h>
 
 #include "chdir-long.h"
-#include "fcntl--.h"
+#include "unistd--.h"
 #include "xgetcwd.h"
 
+#if GNULIB_FCNTL_SAFER
+# include "fcntl--.h"
+#else
+# define GNULIB_FCNTL_SAFER 0
+#endif
+
 /* On systems without the fchdir function (WOE), pretend that open
    always returns -1 so that save_cwd resorts to using xgetcwd.
    Since chdir_long requires fchdir, use chdir instead.  */
@@ -70,6 +76,8 @@ save_cwd (struct saved_cwd *cwd)
   cwd->name = NULL;
 
   cwd->desc = open (".", O_RDONLY);
+  if (!GNULIB_FCNTL_SAFER)
+    cwd->desc = fd_safer (cwd->desc);
   if (cwd->desc < 0)
     {
       cwd->name = xgetcwd ();