io: Implement lchmod using fchmodat [BZ #14578]

include/sys/stat.h

@@ -9,6 +9,7 @@ extern int __lstat (const char *__file, struct stat *__buf);
 extern int __chmod (const char *__file, __mode_t __mode);
 libc_hidden_proto (__chmod)
 extern int __fchmod (int __fd, __mode_t __mode);
+libc_hidden_proto (fchmodat)
 extern __mode_t __umask (__mode_t __mask);
 extern int __mkdir (const char *__path, __mode_t __mode);
 libc_hidden_proto (__mkdir)

io/fchmodat.c

@@ -42,3 +42,4 @@ fchmodat (int fd, const char *file, mode_t mode, int flag)
   return -1;
 }
 stub_warning (fchmodat)
+libc_hidden_def (fchmodat)

io/lchmod.c

@@ -1,4 +1,4 @@
-/* lchmod -- Change the protections of a file or symbolic link.  Stub version.
+/* lchmod -- Change the protections of a file or symbolic link.  Generic version.
    Copyright (C) 2002-2020 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
@@ -17,15 +17,13 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <errno.h>
-#include <sys/stat.h>
+#include <fcntl.h>
 #include <sys/types.h>
+#include <unistd.h>
 
 /* Change the protections of FILE to MODE.  */
 int
 lchmod (const char *file, mode_t mode)
 {
-  __set_errno (ENOSYS);
-  return -1;
+  return fchmodat (AT_FDCWD, file, mode, AT_SYMLINK_NOFOLLOW);
 }
-
-stub_warning (lchmod)

sysdeps/mach/hurd/fchmodat.c

@@ -37,3 +37,4 @@ fchmodat (int fd, const char *file, mode_t mode, int flag)
     return __hurd_fail (err);
   return 0;
 }
+libc_hidden_def (fchmodat)

sysdeps/unix/sysv/linux/fchmodat.c

@@ -38,3 +38,4 @@ fchmodat (int fd, const char *file, mode_t mode, int flag)
 
   return INLINE_SYSCALL (fchmodat, 3, fd, file, mode);
 }
+libc_hidden_def (fchmodat)