Avoid EOVERFLOW problems in some symlink tests

* src/extract.c (is_directory_link): New arg ST.  Caller changed.
(is_directory_link, open_output_file):
Use readlinkat, not fstatat, to determine whether a string
names a symlink.  This avoids EOVERFLOW issues.
(extract_dir): Avoid duplicate calls to fstatat when
keep_directory_symlink_option && fstatat_flags == 0
and the file is a symlink to an existing file.

src/extract.c

@@ -982,18 +982,12 @@ apply_nonancestor_delayed_set_stat (char const *file_name, bool after_links)
 
 
 static bool
-is_directory_link (const char *file_name)
+is_directory_link (char const *file_name, struct stat *st)
 {
-  struct stat st;
-  int e = errno;
-  int res;
-
-  res = (fstatat (chdir_fd, file_name, &st, AT_SYMLINK_NOFOLLOW) == 0 &&
-	 S_ISLNK (st.st_mode) &&
-	 fstatat (chdir_fd, file_name, &st, 0) == 0 &&
-	 S_ISDIR (st.st_mode));
-  errno = e;
-  return res;
+  char buf[1];
+  return (0 <= readlinkat (chdir_fd, file_name, buf, sizeof buf)
+	  && fstatat (chdir_fd, file_name, st, 0) == 0
+	  && S_ISDIR (st->st_mode));
 }
 
 /* Given struct stat of a directory (or directory member) whose ownership
@@ -1066,11 +1060,14 @@ extract_dir (char *file_name, int typeflag)
 	      || old_files_option == OVERWRITE_OLD_FILES))
 	{
 	  struct stat st;
+	  st.st_mode = 0;
 
-	  if (keep_directory_symlink_option && is_directory_link (file_name))
+	  if (keep_directory_symlink_option
+	      && is_directory_link (file_name, &st))
 	    return 0;
 
-	  if (deref_stat (file_name, &st) == 0)
+	  if ((st.st_mode != 0 && fstatat_flags == 0)
+	      || deref_stat (file_name, &st) == 0)
 	    {
 	      current_mode = st.st_mode;
 	      current_mode_mask = ALL_MODE_BITS;
@@ -1178,9 +1175,8 @@ open_output_file (char const *file_name, int typeflag, mode_t mode,
   if (! HAVE_WORKING_O_NOFOLLOW
       && overwriting_old_files && ! dereference_option)
     {
-      struct stat st;
-      if (fstatat (chdir_fd, file_name, &st, AT_SYMLINK_NOFOLLOW) == 0
-	  && S_ISLNK (st.st_mode))
+      char buf[1];
+      if (0 <= readlinkat (chdir_fd, file_name, buf, sizeof buf))
 	{
 	  errno = ELOOP;
 	  return -1;