Reject votes (not consensuses) with >64 known-flags

Our flag voting code needs to handle unrecognized flags, so it stores
them in a 64-bit bitfield.  But we never actually checked for too many
flags, so we were potentially doing stuff like U64_LITERAL(1)<<flagnum
with flagnum >= 64.  That's undefined behavior.

Fix for bug 6833; bugfix on 0.2.0.1-alpha.

changes/bug6833

@@ -0,0 +1,4 @@
+  o Minor bugfixes (directory authority):
+    - Reject consensus votes with more than 64 known-flags. We aren't even
+      close to that limit yet, and our code doesn't handle it
+      correctly. Fixes bug 6833; bugfix on 0.2.0.1-alpha.

src/or/or.h

@@ -2101,6 +2101,9 @@ typedef struct vote_microdesc_hash_t {
 typedef struct vote_routerstatus_t {
   routerstatus_t status; /**< Underlying 'status' object for this router.
                           * Flags are redundant. */
+  /** How many known-flags are allowed in a vote? This is the width of
+   * the flags field of vote_routerstatus_t */
+#define MAX_KNOWN_FLAGS_IN_VOTE 64
   uint64_t flags; /**< Bit-field for all recognized flags; index into
                    * networkstatus_t.known_flags. */
   char *version; /**< The version that the authority says this router is

src/or/routerparse.c

@@ -3004,6 +3004,11 @@ networkstatus_parse_vote_from_string(const char *s, const char **eos_out,
     log_warn(LD_DIR, "known-flags not in order");
     goto err;
   }
+  if (ns->type != NS_TYPE_CONSENSUS &&
+      smartlist_len(ns->known_flags) > MAX_KNOWN_FLAGS_IN_VOTE) {
+    log_warn(LD_DIR, "Too many known-flags in consensus vote or opinion");
+    goto err;
+  }
 
   tok = find_opt_by_keyword(tokens, K_PARAMS);
   if (tok) {