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, 8 insertions, 4 deletions

diff --git a/lib/chdir-long.c b/lib/chdir-long.c
index ba47d59973..afe018d168 100644
--- a/lib/chdir-long.c
+++ b/lib/chdir-long.c
@@ -20,19 +20,23 @@
 
 #include "chdir-long.h"
 
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
 #include <stdlib.h>
 #include <stdbool.h>
 #include <string.h>
-#include <errno.h>
 #include <stdio.h>
-#include <assert.h>
-
-#include "fcntl--.h"
 
 #ifndef PATH_MAX
 # error "compile this file only if your system defines PATH_MAX"
 #endif
 
+/* The results of openat() in this file are not leaked to any
+   single-threaded code that could use stdio.
+   FIXME - if the kernel ever adds support for multi-thread safety for
+   avoiding standard fds, then we should use openat_safer.  */
+
 struct cd_buf
 {
   int fd;