Impose maximum sizes on parsed objects

An object, you'll recall, is something between -----BEGIN----- and
-----END----- tags in a directory document.  Some of our code, as
doorss has noted in bug 2352, could assert if one of these ever
overflowed SIZE_T_CEILING but not INT_MAX.  As a solution, I'm setting
a maximum size on a single object such that neither of these limits
will ever be hit.  I'm also fixing the INT_MAX checks, just to be sure.

changes/bug2352

@@ -0,0 +1,6 @@
+  o Minor bugfixes
+    - Fix some potential asserts and partsing issues with grossly
+      malformed router caches.  Fixes bug 2352.  Found by doorss.
+      Bugfix on Tor 0.2.1.27.
+
+

src/or/routerparse.c

@@ -2549,7 +2549,7 @@ networkstatus_parse_vote_from_string(const char *s, const char **eos_out,
         goto err;
       v->good_signature = 1;
     } else {
-      if (tok->object_size >= INT_MAX)
+      if (tok->object_size >= INT_MAX || tok->object_size >= SIZE_T_CEILING)
         goto err;
       /* We already parsed a vote from this voter. Use the first one. */
       if (v->signature) {
@@ -2700,7 +2700,7 @@ networkstatus_parse_detached_signatures(const char *s, const char *eos)
       voter = tor_malloc_zero(sizeof(networkstatus_voter_info_t));
       memcpy(voter->identity_digest, id_digest, DIGEST_LEN);
       memcpy(voter->signing_key_digest, sk_digest, DIGEST_LEN);
-      if (tok->object_size >= INT_MAX)
+      if (tok->object_size >= INT_MAX || tok->object_size >= SIZE_T_CEILING)
         goto err;
       voter->signature = tor_memdup(tok->object_body, tok->object_size);
       voter->signature_len = (int) tok->object_size;
@@ -3017,6 +3017,10 @@ static directory_token_t *
 get_next_token(memarea_t *area,
                const char **s, const char *eos, token_rule_t *table)
 {
+  /** Reject any object at least this big; it is probably an overflow, an
+   * attack, a bug, or some other nonsense. */
+#define MAX_UNPARSED_OBJECT_SIZE (128*1024)
+
   const char *next, *eol, *obstart;
   size_t obname_len;
   int i;
@@ -3126,6 +3130,9 @@ get_next_token(memarea_t *area,
     ebuf[sizeof(ebuf)-1] = '\0';
     RET_ERR(ebuf);
   }
+  if (next - *s > MAX_UNPARSED_OBJECT_SIZE)
+    RET_ERR("Couldn't parse object: missing footer or object much too big.");
+
   if (!strcmp(tok->object_type, "RSA PUBLIC KEY")) { /* If it's a public key */
     tok->key = crypto_new_pk_env();
     if (crypto_pk_read_public_key_from_string(tok->key, obstart, eol-obstart))