1 files changed, 110 insertions, 0 deletions
diff --git a/lib/lchmod.c b/lib/lchmod.c
new file mode 100644
index 0000000..706dddf
--- /dev/null
+++ b/lib/lchmod.c
@@ -0,0 +1,110 @@
+/* Implement lchmod on platforms where it does not work correctly.
+
+   Copyright 2020-2022 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 Paul Eggert */
+
+#include <config.h>
+
+/* Specification.  */
+#include <sys/stat.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#ifdef __osf__
+/* Write "sys/stat.h" here, not <sys/stat.h>, otherwise OSF/1 5.1 DTK cc
+   eliminates this include because of the preliminary #include <sys/stat.h>
+   above.  */
+# include "sys/stat.h"
+#else
+# include <sys/stat.h>
+#endif
+
+#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)
+{
+#if defined O_PATH && defined AT_EMPTY_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;
+
+  /* Up to Linux 5.3 at least, when FILE refers to a symbolic link, the
+     chmod call below will change the permissions of the symbolic link
+     - which is undesired - and on many file systems (ext4, btrfs, jfs,
+     xfs, ..., but not reiserfs) fail with error EOPNOTSUPP - which is
+     misleading.  Therefore test for a symbolic link explicitly.
+     Use fstatat because fstat does not work on O_PATH descriptors
+     before Linux 3.6.  */
+  struct stat st;
+  if (fstatat (fd, "", &st, AT_EMPTY_PATH) != 0)
+    {
+      int stat_errno = errno;
+      close (fd);
+      errno = stat_errno;
+      return -1;
+    }
+  if (S_ISLNK (st.st_mode))
+    {
+      close (fd);
+      errno = EOPNOTSUPP;
+      return -1;
+    }
+
+# if defined __linux__ || defined __ANDROID__ || defined __CYGWIN__
+  static char const fmt[] = "/proc/self/fd/%d";
+  char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
+  sprintf (buf, fmt, fd);
+  int chmod_result = chmod (buf, mode);
+  int chmod_errno = errno;
+  close (fd);
+  if (chmod_result == 0)
+    return chmod_result;
+  if (chmod_errno != ENOENT)
+    {
+      errno = chmod_errno;
+      return chmod_result;
+    }
+# endif
+  /* /proc is not mounted or would not work as in GNU/Linux.  */
+
+#elif HAVE_LSTAT
+  struct stat st;
+  int lstat_result = lstat (file, &st);
+  if (lstat_result != 0)
+    return lstat_result;
+  if (S_ISLNK (st.st_mode))
+    {
+      errno = EOPNOTSUPP;
+      return -1;
+    }
+#endif
+
+  /* Fall back on chmod, despite a possible race.  */
+  return chmod (file, mode);
+}