Update.

	* sysdeps/generic/libc-start.c: For SUID binaries check whether
	the standard file descriptors are open.
	Reported by Chris Evans <chris@ferret.lmh.ox.ac.uk>.

ChangeLog

@@ -1,5 +1,9 @@
 1999-07-09  Ulrich Drepper  <drepper@cygnus.com>
 
+	* sysdeps/generic/libc-start.c: For SUID binaries check whether
+	the standard file descriptors are open.
+	Reported by Chris Evans <chris@ferret.lmh.ox.ac.uk>.
+
 	* sysdeps/unix/sysv/linux/syscalls.list: Remove mmap64 alias for mmap.
 	* sysdeps/unix/sysv/linux/mmap64.c: Test whether mapped area is in
 	range of mmap.  If not fail.

sysdeps/generic/libc-start.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 1998 Free Software Foundation, Inc.
+/* Copyright (C) 1998, 1999 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -16,8 +16,12 @@
    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
    Boston, MA 02111-1307, USA.  */
 
+#include <errno.h>
+#include <fcntl.h>
+#include <paths.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <sys/ioctl.h>
 #include <elf/ldsodefs.h>
 
 extern void __libc_init_first (int argc, char **argv, char **envp);
@@ -27,6 +31,9 @@ weak_extern (_dl_starting_up)
 extern int __libc_multiple_libcs;
 extern void *__libc_stack_end;
 
+/* Prototype for local function.  */
+static void check_standard_fds (void);
+
 int
 __libc_start_main (int (*main) (int, char **, char **), int argc,
 		   char **argv, void (*init) (void), void (*fini) (void),
@@ -47,6 +54,11 @@ __libc_start_main (int (*main) (int, char **, char **), int argc,
   /* Set the global _environ variable correctly.  */
   __environ = &argv[argc + 1];
 
+  /* Some security at this point.  Prevent starting a SUID binary where
+     the standard file descriptors are not opened.  */
+  if (__libc_enable_secure)
+    check_standard_fds ();
+
   /* Register the destructor of the dynamic linker if there is any.  */
   if (rtld_fini != NULL)
     atexit (rtld_fini);
@@ -77,3 +89,32 @@ __libc_start_main (int (*main) (int, char **, char **), int argc,
 
   exit ((*main) (argc, argv, __environ));
 }
+
+
+/* Should other OSes (e.g., Hurd) have different versions which can
+   be written in a better way?  */
+static void
+check_one_fd (int fd, int mode)
+{
+  if (__fcntl (fd, F_GETFD) == -1 && errno == EBADF)
+    {
+      /* Something is wrong with this descriptor, it's probably not
+	 opened.  Open /dev/null so that the SUID program we are
+	 about to start does not accidently use this descriptor.  */
+      int nullfd = __open (_PATH_DEVNULL, mode);
+      if (nullfd == -1)
+	/* We cannot even given an error message here since it would
+	   run into the same problems.  */
+	abort ();
+    }
+}
+
+
+static void
+check_standard_fds (void)
+{
+/* Check all three standard file descriptors.  */
+  check_one_fd (STDIN_FILENO, O_RDONLY);
+  check_one_fd (STDOUT_FILENO, O_RDWR);
+  check_one_fd (STDERR_FILENO, O_RDWR);
+}