1 files changed, 76 insertions, 0 deletions
diff --git a/lib/opendir-safer.c b/lib/opendir-safer.c
new file mode 100644
index 0000000..1677fb6
--- /dev/null
+++ b/lib/opendir-safer.c
@@ -0,0 +1,76 @@
+/* Invoke opendir, but avoid some glitches.
+
+   Copyright (C) 2009-2022 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Eric Blake.  */
+
+#include <config.h>
+
+#include "dirent-safer.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+/* Like opendir, but do not clobber stdin, stdout, or stderr.  */
+
+DIR *
+opendir_safer (char const *name)
+{
+  DIR *dp = opendir (name);
+
+  if (dp)
+    {
+      int fd = dirfd (dp);
+
+      if (0 <= fd && fd <= STDERR_FILENO)
+        {
+          /* If fdopendir is native (as on Linux), then it is safe to
+             assume dirfd(fdopendir(n))==n.  If we are using the
+             gnulib module fdopendir, then this guarantee is not met,
+             but fdopendir recursively calls opendir_safer up to 3
+             times to at least get a safe fd.  If fdopendir is not
+             present but dirfd is accurate (as on cygwin 1.5.x), then
+             we recurse up to 3 times ourselves.  Finally, if dirfd
+             always fails (as on mingw), then we are already safe.  */
+          DIR *newdp;
+          int e;
+#if HAVE_FDOPENDIR || GNULIB_FDOPENDIR
+          int f = fcntl (fd, F_DUPFD_CLOEXEC, STDERR_FILENO + 1);
+          if (f < 0)
+            {
+              e = errno;
+              newdp = NULL;
+            }
+          else
+            {
+              newdp = fdopendir (f);
+              e = errno;
+              if (! newdp)
+                close (f);
+            }
+#else /* !FDOPENDIR */
+          newdp = opendir_safer (name);
+          e = errno;
+#endif
+          closedir (dp);
+          errno = e;
+          dp = newdp;
+        }
+    }
+
+  return dp;
+}