[taler-anastasis] 01/06: fix #6572

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grothoff pushed a commit to branch master
in repository anastasis.

commit 2f92dc0713cf8745f21c3e7512057afa373e0ac8
Author: Christian Grothoff <christian@grothoff.org>
AuthorDate: Sat Mar 13 15:07:58 2021 +0100

    fix #6572
---
 src/backend/anastasis-httpd_truth.c | 53 ++++++++++++++++++++++++++++---------
 1 file changed, 40 insertions(+), 13 deletions(-)

diff --git a/src/backend/anastasis-httpd_truth.c 
b/src/backend/anastasis-httpd_truth.c
index bf4b182..3d43a94 100644
--- a/src/backend/anastasis-httpd_truth.c
+++ b/src/backend/anastasis-httpd_truth.c
@@ -30,6 +30,13 @@
 #include <taler/taler_merchant_service.h>
 #include <taler/taler_json_lib.h>
 
+/**
+ * What is the maximum frequency at which we allow
+ * clients to attempt to answer security questions?
+ */
+#define MAX_QUESTION_FREQ GNUNET_TIME_relative_multiply ( \
+    GNUNET_TIME_UNIT_SECONDS, 30)
+
 /**
  * How long do we hold an HTTP client connection if
  * we are awaiting payment before giving up?
@@ -894,11 +901,40 @@ AH_handler_truth_get (
                                          
TALER_EC_ANASTASIS_TRUTH_CHALLENGE_RESPONSE_REQUIRED,
                                          NULL);
     }
-    // FIXME: do something here to rate-limit
-    // brute force attempts (by checking against the timestamp
-    // from 'mark_challenge_sent' and refusing if the response
-    // is provided too quickly again!
 
+    {
+      enum GNUNET_DB_QueryStatus qs;
+      struct GNUNET_TIME_Absolute rt;
+      uint64_t code;
+
+      rt = GNUNET_TIME_UNIT_FOREVER_ABS;
+      qs = db->create_challenge_code (db->cls,
+                                      &gc->truth_uuid,
+                                      MAX_QUESTION_FREQ,
+                                      GNUNET_TIME_UNIT_HOURS,
+                                      UINT32_MAX,
+                                      &rt,
+                                      &code);
+      if (0 > qs)
+      {
+        GNUNET_break (0 < qs);
+        GNUNET_free (decrypted_truth);
+        GNUNET_free (truth_mime);
+        return TALER_MHD_reply_with_error (connection,
+                                           MHD_HTTP_INTERNAL_SERVER_ERROR,
+                                           TALER_EC_GENERIC_DB_FETCH_FAILED,
+                                           "create_challenge_code (for rate 
limiting)");
+      }
+      if (0 != rt.abs_value_us)
+      {
+        GNUNET_free (decrypted_truth);
+        GNUNET_free (truth_mime);
+        return TALER_MHD_reply_with_error (connection,
+                                           MHD_HTTP_TOO_MANY_REQUESTS,
+                                           
TALER_EC_ANASTASIS_TRUTH_RATE_LIMITED,
+                                           NULL);
+      }
+    }
     if ( (decrypted_truth_size != sizeof (challenge_response)) ||
          (0 != memcmp (&challenge_response,
                        decrypted_truth,
@@ -910,15 +946,6 @@ AH_handler_truth_get (
                   (unsigned int) sizeof (challenge_response));
       GNUNET_free (decrypted_truth);
       GNUNET_free (truth_mime);
-      /* for rate-limiting... */
-#if 0
-      enum GNUNET_DB_QueryStatus qs;
-      // FIXME: fails: this is an UPDATE statement, we need to possibly INSERT 
_or_ UPDATE
-      qs = db->mark_challenge_sent (db->cls,
-                                    &gc->truth_uuid,
-                                    0);
-      GNUNET_break (0 < qs);
-#endif
       return TALER_MHD_reply_with_error (connection,
                                          MHD_HTTP_FORBIDDEN,
                                          
TALER_EC_ANASTASIS_TRUTH_CHALLENGE_FAILED,

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