Forbid UINT32_MAX as a protocol version

The C code and the rust code had different separate integer overflow
bugs here.  That suggests that we're better off just forbidding this
pathological case.

Also, add tests for expected behavior on receiving a bad protocol
list in a consensus.

Fixes another part of 25249.

changes/bug25249.2

@@ -0,0 +1,3 @@
+  o Minor bugfixes (spec conformance):
+    - Forbid UINT32_MAX as a protocol version.  Fixes part of bug 25249;
+      bugfix on 0.2.9.4-alpha.

src/or/protover.c

@@ -103,6 +103,9 @@ proto_entry_free(proto_entry_t *entry)
   tor_free(entry);
 }
 
+/** The largest possible protocol version. */
+#define MAX_PROTOCOL_VERSION (UINT32_MAX-1)
+
 /**
  * Given a string <b>s</b> and optional end-of-string pointer
  * <b>end_of_range</b>, parse the protocol range and store it in
@@ -130,7 +133,7 @@ parse_version_range(const char *s, const char *end_of_range,
 
   /* Note that this wouldn't be safe if we didn't know that eventually,
    * we'd hit a NUL */
-  low = (uint32_t) tor_parse_ulong(s, 10, 0, UINT32_MAX, &ok, &next);
+  low = (uint32_t) tor_parse_ulong(s, 10, 0, MAX_PROTOCOL_VERSION, &ok, &next);
   if (!ok)
     goto error;
   if (next > end_of_range)
@@ -148,7 +151,8 @@ parse_version_range(const char *s, const char *end_of_range,
   if (!TOR_ISDIGIT(*s)) {
     goto error;
   }
-  high = (uint32_t) tor_parse_ulong(s, 10, 0, UINT32_MAX, &ok, &next);
+  high = (uint32_t) tor_parse_ulong(s, 10, 0,
+                                    MAX_PROTOCOL_VERSION, &ok, &next);
   if (!ok)
     goto error;
   if (next != end_of_range)

src/test/test_protover.c

@@ -257,12 +257,27 @@ test_protover_all_supported(void *arg)
   tt_str_op(msg, OP_EQ, "Sleen=0-2147483648");
   tor_free(msg);
 
-  /* Rust seems to experience an internal error here */
-  tt_assert(! protover_all_supported("Sleen=0-4294967295", &msg));
-  tt_str_op(msg, OP_EQ, "Sleen=0-4294967295");
+  /* This case is allowed. */
+  tt_assert(! protover_all_supported("Sleen=0-4294967294", &msg));
+  tt_str_op(msg, OP_EQ, "Sleen=0-4294967294");
   tor_free(msg);
 
+  /* If we get an unparseable list, we say "yes, that's supported." */
+  tor_capture_bugs_(1);
+  tt_assert(protover_all_supported("Fribble", &msg));
+  tt_ptr_op(msg, OP_EQ, NULL);
+  tor_end_capture_bugs_();
+
+  /* This case is forbidden. Since it came from a protover_all_supported,
+   * it can trigger a bug message.  */
+  tor_capture_bugs_(1);
+  tt_assert(protover_all_supported("Sleen=0-4294967295", &msg));
+  tt_ptr_op(msg, OP_EQ, NULL);
+  tor_free(msg);
+  tor_end_capture_bugs_();
+
  done:
+  tor_end_capture_bugs_();
   tor_free(msg);
 }