2005-12-13 Ulrich Drepper <drepper@redhat.com>

1 files changed, 102 insertions, 0 deletions

diff --git a/csu/check_fds.c b/csu/check_fds.c
new file mode 100644
index 0000000..10ba3da
--- /dev/null
+++ b/csu/check_fds.c
@@ -0,0 +1,102 @@
+/* Copyright (C) 2000, 2002, 2003, 2005 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
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, 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 <unistd.h>
+#include <sys/stat.h>
+#include <sys/sysmacros.h>
+
+/* Try to get a machine dependent instruction which will make the
+   program crash.  This is used in case everything else fails.  */
+#include <abort-instr.h>
+#ifndef ABORT_INSTRUCTION
+/* No such instruction is available.  */
+# define ABORT_INSTRUCTION
+#endif
+
+#include <device-nrs.h>
+#include <not-cancel.h>
+
+
+/* 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)
+{
+  /* Note that fcntl() with this parameter is not a cancellation point.  */
+  if (__builtin_expect (__libc_fcntl (fd, F_GETFD), 0) == -1
+      && errno == EBADF)
+    {
+      const char *name;
+      dev_t dev;
+
+      /* For writable descriptors we use /dev/full.  */
+      if ((mode & O_ACCMODE) == O_WRONLY)
+	{
+	  name = _PATH_DEV "full";
+	  dev = makedev (DEV_FULL_MAJOR, DEV_FULL_MINOR);
+	}
+      else
+	{
+	  name = _PATH_DEVNULL;
+	  dev = makedev (DEV_NULL_MAJOR, DEV_NULL_MINOR);
+	}
+
+      /* 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_not_cancel (name, mode, 0);
+
+      /* We are very paranoid here.  With all means we try to ensure
+	 that we are actually opening the /dev/null device and nothing
+	 else.
+
+	 Note that the following code assumes that STDIN_FILENO,
+	 STDOUT_FILENO, STDERR_FILENO are the three lowest file
+	 decsriptor numbers, in this order.  */
+      struct stat64 st;
+      if (__builtin_expect (nullfd != fd, 0)
+	  || __builtin_expect (__fxstat64 (_STAT_VER, fd, &st), 0) != 0
+	  || __builtin_expect (S_ISCHR (st.st_mode), 1) == 0
+	  || st.st_rdev != dev)
+	/* We cannot even give an error message here since it would
+	   run into the same problems.  */
+	while (1)
+	  /* Try for ever and ever.  */
+	  ABORT_INSTRUCTION;
+    }
+}
+
+
+void
+__libc_check_standard_fds (void)
+{
+  /* This is really paranoid but some people actually are.  If /dev/null
+     should happen to be a symlink to somewhere else and not the device
+     commonly known as "/dev/null" we bail out.  We can detect this with
+     the O_NOFOLLOW flag for open() but only on some system.  */
+#ifndef O_NOFOLLOW
+# define O_NOFOLLOW	0
+#endif
+  /* Check all three standard file descriptors.  */
+  check_one_fd (STDIN_FILENO, O_WRONLY | O_NOFOLLOW);
+  check_one_fd (STDOUT_FILENO, O_RDONLY | O_NOFOLLOW);
+  check_one_fd (STDERR_FILENO, O_RDONLY | O_NOFOLLOW);
+}