url-http-ntlm: Prevent infinite loops

* url-http-ntlm.el (url-http-ntlm--loop-timer-counter): New
variable.
(url-http-ntlm--detect-loop): New function.
(url-ntlm-auth): Call url-http-ntlm--detect-loop before handling a
request or response.

diff --git a/packages/url-http-ntlm/url-http-ntlm.el b/packages/url-http-ntlm/url-http-ntlm.el
index 362f2ccb59780056e9bafdf27f1839162e148bf9..ce649f8d9e62aaae686fe696d7ca67d2c2f972bf 100644 (file)
--- a/packages/url-http-ntlm/url-http-ntlm.el
+++ b/packages/url-http-ntlm/url-http-ntlm.el
@@ -67,8 +67,42 @@ Note that for any server, only one user and password is ever stored.")
 This is used to detect multiple calls.")
 (make-variable-buffer-local 'url-http-ntlm--last-args)
 
+(defvar url-http-ntlm--loop-timer-counter nil
+  "A hash table used to detect NTLM negotiation errors.
+Keys are urls, entries are (START-TIME . COUNTER).")
+
 \f
 ;;; Private functions.
+(defun url-http-ntlm--detect-loop (url)
+  "Detect potential infinite loop when NTLM fails on URL."
+  (when (not url-http-ntlm--loop-timer-counter)
+    (setq url-http-ntlm--loop-timer-counter (make-hash-table :test 'equal)))
+  (let* ((url-string (url-recreate-url url))
+        (last-entry (gethash url-string url-http-ntlm--loop-timer-counter))
+        (start-time (car last-entry))
+        (counter (cdr last-entry)))
+    (if last-entry
+       (progn
+         (if (< (-  (float-time) start-time) 10.0)
+             (if (< counter 20)
+                 ;; Still within time window, so increment count.
+                 (puthash url-string (cons start-time (1+ counter))
+                          url-http-ntlm--loop-timer-counter)
+               ;; Error detected, so remove entry and clear.
+               (url-http-ntlm--authorisation url-string :clear)
+               (remhash url-string url-http-ntlm--loop-timer-counter)
+               (error
+                (format (concat "Access rate to %s is too high,"
+                                " indicating an NTLM failure;"
+                                " to debug, re-run with url-debug set to 1")
+                        url-string)))
+           ;; Timeout expired, so reset counter.
+           (puthash url-string (cons (float-time) 0)
+                    url-http-ntlm--loop-timer-counter)))
+      ;; New access, so initialize counter to 0.
+      (puthash url-string (cons (float-time) 0)
+              url-http-ntlm--loop-timer-counter))))
+
 (defun url-http-ntlm--ensure-keepalive ()
   "Report an error if `url-http-attempt-keepalives' is not set."
   (cl-assert url-http-attempt-keepalives
@@ -200,6 +234,7 @@ the server's last response.  These are used by
     (cl-case stage
       ;; NTLM Type 1 message: the request
       (:request
+       (url-http-ntlm--detect-loop user-url)
        (cl-destructuring-bind (&optional server user hash)
           (url-http-ntlm--authorisation url)
         (when server
@@ -207,6 +242,7 @@ the server's last response.  These are used by
            (ntlm-build-auth-request user server)))))
       ;; NTLM Type 3 message: the response
       (:response
+       (url-http-ntlm--detect-loop user-url)
        (let ((challenge (url-http-ntlm--get-challenge)))
         (cl-destructuring-bind (server user hash)
             (url-http-ntlm--authorisation url)