Make "unsafe directory" error message more informative (Bug#865)

* lisp/server.el (server-ensure-safe-dir): Produce a description for
each "unsafe" condition.

1 files changed, 26 insertions, 21 deletions

diff --git a/lisp/server.el b/lisp/server.el
index 8aafa1c2570..33800a98682 100644
--- a/lisp/server.el
+++ b/lisp/server.el
@@ -525,30 +525,35 @@ Creates the directory if necessary and makes sure:
     ;; Check that it's safe for use.
     (let* ((uid (nth 2 attrs))
            (w32 (eq system-type 'windows-nt))
-           (safe (cond
-                  ((not (eq t (car attrs))) nil)  ; is a dir?
-                  ((and w32 (zerop uid))          ; on FAT32?
-                   (display-warning
-                    'server
-                    (format-message "\
+           (unsafe (cond
+                    ((not (eq t (car attrs)))
+                     (format "it is a %s" (if (stringp (car attrs))
+                                              "symlink" "file")))
+                    ((and w32 (zerop uid)) ; on FAT32?
+                     (display-warning
+                      'server
+                      (format-message "\
 Using `%s' to store Emacs-server authentication files.
 Directories on FAT32 filesystems are NOT secure against tampering.
 See variable `server-auth-dir' for details."
-                            (file-name-as-directory dir))
-                    :warning)
-                   t)
-                  ((and (/= uid (user-uid))       ; is the dir ours?
-                        (or (not w32)
-                            ;; Files created on Windows by Administrator
-                            ;; (RID=500) have the Administrators (RID=544)
-                            ;; group recorded as the owner.
-                            (/= uid 544) (/= (user-uid) 500)))
-                   nil)
-                  (w32 t)                         ; on NTFS?
-                  (t                              ; else, check permissions
-                   (zerop (logand ?\077 (file-modes dir)))))))
-      (unless safe
-        (error "The directory `%s' is unsafe" dir)))))
+                                      (file-name-as-directory dir))
+                      :warning)
+                     nil)
+                    ((and (/= uid (user-uid)) ; is the dir ours?
+                          (or (not w32)
+                              ;; Files created on Windows by Administrator
+                              ;; (RID=500) have the Administrators (RID=544)
+                              ;; group recorded as the owner.
+                              (/= uid 544) (/= (user-uid) 500)))
+                     (format "it is not owned by you (owner = %s (%d))"
+                             (user-full-name (user-uid)) (user-uid)))
+                    (w32 nil)           ; on NTFS?
+                    ((/= 0 (logand ?\077 (file-modes dir)))
+                     (format "it is accessible by others (%03o)"
+                             (file-modes dir)))
+                    (t nil))))
+      (when unsafe
+        (error "`%s' is not a safe directory because %s" dir unsafe)))))
 
 (defun server-generate-key ()
   "Generate and return a random authentication key.