protover: Move all hardcoded lists in one place

This also moves the warnings and add some theatrical effect around the
code so anyone modifying those list should notice the warnings signs and
read the comment accordingly.

Signed-off-by: David Goulet <dgoulet@torproject.org>

src/core/or/protover.c

@@ -376,6 +376,10 @@ protocol_list_supports_protocol_or_later(const char *list,
   return contains;
 }
 
+/*
+ * XXX START OF HAZARDOUS ZONE XXX
+ */
+
 /** Return the canonical string containing the list of protocols
  * that we support.
  **/
@@ -383,25 +387,37 @@ protocol_list_supports_protocol_or_later(const char *list,
 const char *
 protover_get_supported_protocols(void)
 {
+
   /*
-   * WARNING!
+   * XXX: WARNING!
    *
    * Be EXTREMELY CAREFUL when *removing* versions from this list.  If you
    * remove an entry while it still appears as "recommended" in the consensus,
-   * you'll cause all the instances without it to warn.  If you remove an entry
-   * while it still appears as "required" in the consensus, you'll cause
-   * all the instances without it to refuse to connect to the network, and
-   * shut down.
+   * you'll cause all the instances without it to warn.
    *
-   * If you need to remove a version from this list, you need to make sure
-   * that it is not listed in the _current consensuses_: just removing it from
-   * the required list in dirvote.c is NOT ENOUGH.  You need to remove it from
-   * the required list dirvote.c, and THEN let the authorities update and vote
-   * on new consensuses without it.  Only once those consensuses are out is
-   * it safe to remove from this list.
+   * If you remove an entry while it still appears as "required" in the
+   * consensus, you'll cause all the instances without it to refuse to connect
+   * to the network, and shut down.
    *
-   * WARNING!
+   * If you need to remove a version from this list, you need to make sure that
+   * it is not listed in the _current consensuses_: just removing it from the
+   * required list below is NOT ENOUGH.  You need to remove it from the
+   * required list, and THEN let the authorities update and vote on new
+   * consensuses without it. Only once those consensuses are out is it safe to
+   * remove from this list.
+   *
+   * One concrete example of a very dangerous race that could occur:
+   *
+   * If the client required protocol "HSDir=1-2" is then changed in the code
+   * and released to "HSDir=2" while the consensus stills lists "HSDir=1-2",
+   * then these clients, even very recent ones, will shutdown because they
+   * don't support "HSDir=1".
+   *
+   * And so, changes need to be done in lockstep as described above.
+   *
+   * XXX: WARNING!
    */
+
   return
     "Cons=1-2 "
     "Desc=1-2 "
@@ -419,6 +435,73 @@ protover_get_supported_protocols(void)
     "Relay=1-2";
 }
 
+/*
+ * XXX: WARNING!
+ *
+ * The recommended and required values are hardwired, to avoid disaster. Voting
+ * on the wrong subprotocols here has the potential to take down the network.
+ *
+ * In particular, you need to be EXTREMELY CAREFUL before adding new versions
+ * to the required protocol list.  Doing so will cause every relay or client
+ * that doesn't support those versions to refuse to connect to the network and
+ * shut down.
+ *
+ * Note that this applies to versions, not just protocols!  If you say that
+ * Foobar=8-9 is required, and the client only has Foobar=9, it will shut down.
+ *
+ * It is okay to do this only for SUPER OLD relays that are not supported on
+ * the network anyway.  For clients, we really shouldn't kick them off the
+ * network unless their presence is causing serious active harm.
+ *
+ * The following required and recommended lists MUST be changed BEFORE the
+ * supported list above is changed in order for those lists to appear in the
+ * consensus BEFORE.
+ *
+ * Please, see the warning in protocol_get_supported_versions().
+ *
+ * XXX: WARNING!
+ */
+
+/** Return the recommended client protocols list that directory authorities
+ * put in the consensus. */
+const char *
+protover_get_recommended_client_protocols(void)
+{
+  return "Cons=1-2 Desc=1-2 DirCache=1 HSDir=1 HSIntro=3 HSRend=1 "
+         "Link=4 Microdesc=1-2 Relay=2";
+}
+
+/** Return the recommended relay protocols list that directory authorities
+ * put in the consensus. */
+const char *
+protover_get_recommended_relay_protocols(void)
+{
+  return "Cons=1-2 Desc=1-2 DirCache=1 HSDir=1 HSIntro=3 HSRend=1 "
+         "Link=4 Microdesc=1-2 Relay=2";
+}
+
+/** Return the required client protocols list that directory authorities
+ * put in the consensus. */
+const char *
+protover_get_required_client_protocols(void)
+{
+  return "Cons=1-2 Desc=1-2 DirCache=1 HSDir=1 HSIntro=3 HSRend=1 "
+         "Link=4 Microdesc=1-2 Relay=2";
+}
+
+/** Return the required relay protocols list that directory authorities
+ * put in the consensus. */
+const char *
+protover_get_required_relay_protocols(void)
+{
+  return "Cons=1 Desc=1 DirCache=1 HSDir=1 HSIntro=3 HSRend=1 "
+         "Link=3-4 Microdesc=1 Relay=1-2";
+}
+
+/*
+ * XXX END OF HAZARDOUS ZONE XXX
+ */
+
 /** The protocols from protover_get_supported_protocols(), as parsed into a
  * list of proto_entry_t values. Access this via
  * get_supported_protocol_list. */

src/core/or/protover.h

@@ -49,6 +49,10 @@ bool protover_contains_long_protocol_names(const char *s);
 int protover_all_supported(const char *s, char **missing);
 int protover_is_supported_here(protocol_type_t pr, uint32_t ver);
 const char *protover_get_supported_protocols(void);
+const char *protover_get_recommended_client_protocols(void);
+const char *protover_get_recommended_relay_protocols(void);
+const char *protover_get_required_client_protocols(void);
+const char *protover_get_required_relay_protocols(void);
 
 char *protover_compute_vote(const struct smartlist_t *list_of_proto_strings,
                             int threshold);

src/feature/dirauth/dirvote.c

@@ -180,7 +180,7 @@ format_protocols_lines_for_vote(const networkstatus_t *v3_ns)
   char *required_relay_protocols_line = NULL;
   char *required_client_protocols_line = NULL;
 
-   recommended_relay_protocols_line =
+  recommended_relay_protocols_line =
     format_line_if_present("recommended-relay-protocols",
                            v3_ns->recommended_relay_protocols);
   recommended_client_protocols_line =
@@ -4577,41 +4577,14 @@ dirserv_generate_networkstatus_vote_obj(crypto_pk_t *private_key,
   v3_out->client_versions = client_versions;
   v3_out->server_versions = server_versions;
 
-  /*
-   * WARNING!
-   *
-   * These values are hardwired, to avoid disaster. Voting on the wrong
-   * subprotocols here has the potential to take down the network.
-   *
-   * In particular, you need to be EXTREMELY CAREFUL before adding new
-   * versions to the required protocol list.  Doing so will cause every relay
-   * or client that doesn't support those versions to refuse to connect to the
-   * network and shut down.
-   *
-   * Note that this applies to versions, not just protocols!  If you say that
-   * Foobar=8-9 is required, and the client only has Foobar=9, it will shut
-   * down.
-   *
-   * It is okay to do this only for SUPER OLD relays that are not supported on
-   * the network anyway.  For clients, we really shouldn't kick them off the
-   * network unless their presence is causing serious active harm.
-   *
-   * See also the warning in protocol_get_supported_versions().
-   *
-   * WARNING!
-   */
   v3_out->recommended_relay_protocols =
-    tor_strdup("Cons=1-2 Desc=1-2 DirCache=1 HSDir=1 HSIntro=3 HSRend=1 "
-               "Link=4 Microdesc=1-2 Relay=2");
+    tor_strdup(protover_get_recommended_relay_protocols());
   v3_out->recommended_client_protocols =
-    tor_strdup("Cons=1-2 Desc=1-2 DirCache=1 HSDir=1 HSIntro=3 HSRend=1 "
-               "Link=4 Microdesc=1-2 Relay=2");
+    tor_strdup(protover_get_recommended_client_protocols());
   v3_out->required_client_protocols =
-    tor_strdup("Cons=1-2 Desc=1-2 DirCache=1 HSDir=1 HSIntro=3 HSRend=1 "
-               "Link=4 Microdesc=1-2 Relay=2");
+    tor_strdup(protover_get_required_client_protocols());
   v3_out->required_relay_protocols =
-    tor_strdup("Cons=1 Desc=1 DirCache=1 HSDir=1 HSIntro=3 HSRend=1 "
-               "Link=3-4 Microdesc=1 Relay=1-2");
+    tor_strdup(protover_get_required_relay_protocols());
 
   /* We are not allowed to vote to require anything we don't have. */
   tor_assert(protover_all_supported(v3_out->required_relay_protocols, NULL));