linux: Make fdopendir fail with O_PATH (BZ 30373)

It is not strictly required by the POSIX, since O_PATH is a Linux
extension, but it is QoI to fail early instead of at readdir.  Also
the check is free, since fdopendir already checks if the file
descriptor is opened for read.

Checked on x86_64-linux-gnu.

3 files changed, 56 insertions, 1 deletions

diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 250df6f455..415aa1f14d 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -201,6 +201,7 @@ tests += \
   tst-clone3 \
   tst-epoll \
   tst-fanotify \
+  tst-fdopendir-o_path \
   tst-getauxval \
   tst-gettid \
   tst-gettid-kill \
diff --git a/sysdeps/unix/sysv/linux/fdopendir.c b/sysdeps/unix/sysv/linux/fdopendir.c
index 861345396c..707fb5960e 100644
--- a/sysdeps/unix/sysv/linux/fdopendir.c
+++ b/sysdeps/unix/sysv/linux/fdopendir.c
@@ -37,10 +37,16 @@ __fdopendir (int fd)
       return NULL;
     }
 
-  /* Make sure the descriptor allows for reading.  */
   int flags = __fcntl64_nocancel (fd, F_GETFL);
   if (__glibc_unlikely (flags == -1))
     return NULL;
+  /* Fail early for descriptors opened with O_PATH.  */
+  if (__glibc_unlikely (flags & O_PATH))
+    {
+      __set_errno (EBADF);
+      return NULL;
+    }
+  /* Make sure the descriptor allows for reading.  */
   if (__glibc_unlikely ((flags & O_ACCMODE) == O_WRONLY))
     {
       __set_errno (EINVAL);
diff --git a/sysdeps/unix/sysv/linux/tst-fdopendir-o_path.c b/sysdeps/unix/sysv/linux/tst-fdopendir-o_path.c
new file mode 100644
index 0000000000..2531cf8ddb
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-fdopendir-o_path.c
@@ -0,0 +1,48 @@
+/* Check if fdopendir fails with file descriptor opened with O_PATH (BZ 30737)
+   Copyright (C) 2023 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, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <dirent.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <support/xunistd.h>
+
+static int
+do_test (void)
+{
+  char *dirname = support_create_temp_directory ("tst-fdopendir-o_path");
+
+  {
+    int fd = xopen (dirname, O_RDONLY |  O_DIRECTORY, 0600);
+    DIR *dir = fdopendir (fd);
+    TEST_VERIFY_EXIT (dir != NULL);
+    closedir (dir);
+  }
+
+  {
+    int fd = xopen (dirname, O_RDONLY | O_PATH | O_DIRECTORY, 0600);
+    TEST_VERIFY (fdopendir (fd) == NULL);
+    TEST_COMPARE (errno, EBADF);
+    xclose (fd);
+  }
+
+  return 0;
+}
+
+#include <support/test-driver.c>