1 files changed, 94 insertions, 0 deletions
diff --git a/lib/lchmod.c b/lib/lchmod.c
new file mode 100644
index 0000000..b2d1b8b
--- /dev/null
+++ b/lib/lchmod.c
@@ -0,0 +1,94 @@
+/* Implement lchmod on platforms where it does not work correctly.
+
+   Copyright 2020-2023 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 Paul Eggert */
+
+#include <config.h>
+
+/* Specification.  */
+#include <sys/stat.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <intprops.h>
+
+/* Work like chmod, except when FILE is a symbolic link.
+   In that case, on systems where permissions on symbolic links are unsupported
+   (such as Linux), set errno to EOPNOTSUPP and return -1.  */
+
+int
+lchmod (char const *file, mode_t mode)
+{
+  char readlink_buf[1];
+
+#ifdef O_PATH
+  /* Open a file descriptor with O_NOFOLLOW, to make sure we don't
+     follow symbolic links, if /proc is mounted.  O_PATH is used to
+     avoid a failure if the file is not readable.
+     Cf. <https://sourceware.org/bugzilla/show_bug.cgi?id=14578>  */
+  int fd = open (file, O_PATH | O_NOFOLLOW | O_CLOEXEC);
+  if (fd < 0)
+    return fd;
+
+  int err;
+  if (0 <= readlinkat (fd, "", readlink_buf, sizeof readlink_buf))
+    err = EOPNOTSUPP;
+  else if (errno == EINVAL)
+    {
+      static char const fmt[] = "/proc/self/fd/%d";
+      char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
+      sprintf (buf, fmt, fd);
+      err = chmod (buf, mode) == 0 ? 0 : errno == ENOENT ? -1 : errno;
+    }
+  else
+    err = errno == ENOENT ? -1 : errno;
+
+  close (fd);
+
+  errno = err;
+  if (0 <= err)
+    return err == 0 ? 0 : -1;
+#endif
+
+  size_t len = strlen (file);
+  if (len && file[len - 1] == '/')
+    {
+      struct stat st;
+      if (lstat (file, &st) < 0)
+        return -1;
+      if (!S_ISDIR (st.st_mode))
+        {
+          errno = ENOTDIR;
+          return -1;
+        }
+    }
+
+  /* O_PATH + /proc is not supported.  */
+
+  if (0 <= readlink (file, readlink_buf, sizeof readlink_buf))
+    {
+      errno = EOPNOTSUPP;
+      return -1;
+    }
+
+  /* Fall back on chmod, despite a possible race.  */
+  return chmod (file, mode);
+}