Improve symlinks for Tramp

* lisp/files.el (files--splice-dirname-file): Quote whole file.

* lisp/net/tramp-sh.el (tramp-sh-handle-make-symbolic-link):
Do not expand TARGET, it could be remote.
(tramp-sh-handle-file-truename): Check for cyclic symlink also
in case of readlink.  Quote result if it looks remote.
(tramp-sh-handle-file-local-copy): Use `file-truename'.

* test/lisp/net/tramp-tests.el (tramp-test08-file-local-copy)
(tramp-test09-insert-file-contents): Test also file missing.
(tramp-test21-file-links): Extend test.

1 files changed, 13 insertions, 5 deletions

diff --git a/lisp/net/tramp-sh.el b/lisp/net/tramp-sh.el
index 6494b0957bf..85966f122d2 100644
--- a/lisp/net/tramp-sh.el
+++ b/lisp/net/tramp-sh.el
@@ -1086,7 +1086,7 @@ component is used as the target of the symlink."
         ;; If TARGET is a Tramp name, use just the localname component.
         (when (and (tramp-tramp-file-p target)
                    (tramp-file-name-equal-p
-                    v (tramp-dissect-file-name (expand-file-name target))))
+                    v (tramp-dissect-file-name target)))
           (setq target
                 (tramp-file-name-localname
                  (tramp-dissect-file-name (expand-file-name target)))))
@@ -1132,7 +1132,12 @@ component is used as the target of the symlink."
                      (tramp-shell-quote-argument localname)))
             (with-current-buffer (tramp-get-connection-buffer v)
               (goto-char (point-min))
-              (setq result (buffer-substring (point-min) (point-at-eol)))))
+              (setq result (buffer-substring (point-min) (point-at-eol))))
+            (when (and (file-symlink-p filename)
+                       (string-equal result localname))
+              (tramp-error
+               v 'file-error
+               "Apparent cycle of symbolic links for %s" filename)))
 
            ;; Use Perl implementation.
            ((and (tramp-get-remote-perl v)
@@ -1214,8 +1219,11 @@ component is used as the target of the symlink."
                         "/"))
                 (when (string= "" result)
                   (setq result "/")))))
-
-          (when quoted (setq result (tramp-compat-file-name-quote result)))
+          ;; If the resulting localname looks remote, we must quote it
+          ;; for security reasons.
+          (when (or quoted (file-remote-p result))
+            (let (file-name-handler-alist)
+              (setq result (tramp-compat-file-name-quote result))))
           (tramp-message v 4 "True name of `%s' is `%s'" localname result)
           result))))
 
@@ -3072,7 +3080,7 @@ the result will be a local, non-Tramp, file name."
 (defun tramp-sh-handle-file-local-copy (filename)
   "Like `file-local-copy' for Tramp files."
   (with-parsed-tramp-file-name filename nil
-    (unless (file-exists-p filename)
+    (unless (file-exists-p (file-truename filename))
       (tramp-error
        v tramp-file-missing
        "Cannot make local copy of non-existing file `%s'" filename))