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authorUlrich Drepper <drepper@redhat.com>2005-12-14 08:43:25 +0000
committerUlrich Drepper <drepper@redhat.com>2005-12-14 08:43:25 +0000
commitb6ab06cef4670e02756bcdd4d2c33a49369a4346 (patch)
treeb30743eb9728d890d1519f62b2d1f2b96f62547a /csu/check_fds.c
parentd1dc39a44e339f9c48baa3854fffb3d68c73c8fa (diff)
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2005-12-13 Ulrich Drepper <drepper@redhat.com>
Diffstat (limited to 'csu/check_fds.c')
-rw-r--r--csu/check_fds.c102
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);
+}