fdopendir: fix GNU/Hurd bug

fdopendir(open("file",O_RDONLY)) mistakenly succeeded, with
subsequent readdir() failing with ENOTDIR.

* m4/fdopendir.m4 (gl_FUNC_FDOPENDIR): Check for Hurd bug in
allowing non-directory fds.
* lib/fdopendir.c (rpl_fdopendir): Work around it.
* m4/dirent_h.m4 (gl_DIRENT_H_DEFAULTS): New witness.
* modules/dirent (Makefile.am): Substitute it.
* lib/dirent.in.h (fdopendir): Declare replacement.
* doc/posix-functions/fdopendir.texi (fdopendir): Document this.
* tests/test-fdopendir.c (main): Test something other than
/dev/null, since on Hurd that behaves like a directory.

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

1 files changed, 36 insertions, 9 deletions

diff --git a/lib/fdopendir.c b/lib/fdopendir.c
index 14dc111c81..c364306630 100644
--- a/lib/fdopendir.c
+++ b/lib/fdopendir.c
@@ -23,13 +23,15 @@
 #include <stdlib.h>
 #include <unistd.h>
 
-#include "openat.h"
-#include "openat-priv.h"
-#include "save-cwd.h"
+#if !HAVE_FDOPENDIR
 
-#if GNULIB_DIRENT_SAFER
-# include "dirent--.h"
-#endif
+# include "openat.h"
+# include "openat-priv.h"
+# include "save-cwd.h"
+
+# if GNULIB_DIRENT_SAFER
+#  include "dirent--.h"
+# endif
 
 /* Replacement for Solaris' function by the same name.
    <http://www.google.com/search?q=fdopendir+site:docs.sun.com>
@@ -70,12 +72,12 @@ fdopendir (int fd)
      save_cwd/restore_cwd.  */
   if (! dir && EXPECTED_ERRNO (saved_errno))
     {
-#if REPLACE_FCHDIR
+# if REPLACE_FCHDIR
       const char *name = _gl_directory_name (fd);
       if (name)
         dir = opendir (name);
       saved_errno = errno;
-#else /* !REPLACE_FCHDIR */
+# else /* !REPLACE_FCHDIR */
       struct saved_cwd saved_cwd;
       if (save_cwd (&saved_cwd) != 0)
 	openat_save_fail (errno);
@@ -95,7 +97,7 @@ fdopendir (int fd)
 	}
 
       free_cwd (&saved_cwd);
-#endif /* !REPLACE_FCHDIR */
+# endif /* !REPLACE_FCHDIR */
     }
 
   if (dir)
@@ -105,3 +107,28 @@ fdopendir (int fd)
   errno = saved_errno;
   return dir;
 }
+
+#else /* HAVE_FDOPENDIR */
+
+# include <errno.h>
+# include <sys/stat.h>
+
+# undef fdopendir
+
+/* Like fdopendir, but work around GNU/Hurd bug by validating FD.  */
+
+DIR *
+rpl_fdopendir (int fd)
+{
+  struct stat st;
+  if (fstat (fd, &st))
+    return NULL;
+  if (!S_ISDIR (st.st_mode))
+    {
+      errno = ENOTDIR;
+      return NULL;
+    }
+  return fdopendir (fd);
+}
+
+#endif /* HAVE_FDOPENDIR */