Warn about redundant torrc ExitPolicy lines due to accept/reject *:*

Tor now warns when ExitPolicy lines occur after accept/reject *:*
or variants. These lines are redundant, and were always ignored.

Partial fix for ticket 16069. Patch by "teor".
Patch on 2eb7eafc9d and a96c0affcb (25 Oct 2012),
released in 0.2.4.7-alpha.

changes/bug16069-exit-policy-rule6

@@ -7,6 +7,8 @@
       * a "private" address alias is used on an accept6 or reject6 line.
         The line filters both IPv4 and IPv6 private addresses, disregarding
         the 6 in accept6/reject6.
+      * any ExitPolicy lines occur after accept/reject *:* or variants.
+        These are redundant, and were always ignored.
     - When parsing torrc ExitPolicies, we now issue an info-level message:
       * when expanding an accept/reject * line to include both IPv4 and IPv6
         wildcard addresses.

src/or/policies.c

@@ -1013,6 +1013,66 @@ policies_parse_exit_policy_internal(config_line_t *cfg, smartlist_t **dest,
   }
   if (parse_addr_policy(cfg, dest, -1))
     return -1;
+
+  /* Before we add the default policy and final rejects, check to see if
+   * there are any lines after accept *:* or reject *:*. These lines have no
+   * effect, and are most likely an error. */
+  int found_final_effective_entry = 0;
+  int first_redundant_entry = 0;
+  for (int i = 0; i < smartlist_len(*dest); ++i) {
+    sa_family_t family;
+    addr_policy_t *p;
+    int found_ipv4_wildcard = 0, found_ipv6_wildcard = 0;
+
+    p = smartlist_get(*dest, i);
+
+    /* Look for accept/reject *[4|6|]:* entires */
+    if (p->prt_min <= 1 && p->prt_max == 65535 && p->maskbits == 0) {
+      family = tor_addr_family(&p->addr);
+      /* accept/reject *:* may have already been expanded into
+       * accept/reject *4:*,accept/reject *6:*
+       * But handle both forms.
+       */
+      if (family == AF_INET || family == AF_UNSPEC) {
+        found_ipv4_wildcard = 1;
+      }
+      if (family == AF_INET6 || family == AF_UNSPEC) {
+        found_ipv6_wildcard = 1;
+      }
+    }
+
+    /* We also find accept *4:*,reject *6:* ; and
+     * accept *4:*,<other policies>,accept *6:* ; and similar.
+     * That's ok, because they make any subsequent entries redundant. */
+    if (found_ipv4_wildcard && found_ipv6_wildcard) {
+      found_final_effective_entry = 1;
+      /* if we're not on the final entry in the list */
+      if (i < smartlist_len(*dest) - 1) {
+        first_redundant_entry = i + 1;
+      }
+      break;
+    }
+  }
+  /* Work out if there are redundant trailing entries in the policy list */
+  if (found_final_effective_entry && first_redundant_entry > 0) {
+    addr_policy_t *p;
+    /* Longest possible policy is
+     * "accept6 ffff:ffff:..255/128:10000-65535",
+     * which contains a max-length IPv6 address, plus 24 characters. */
+    char line[TOR_ADDR_BUF_LEN + 32];
+
+    tor_assert(first_redundant_entry < smartlist_len(*dest));
+    p = smartlist_get(*dest, first_redundant_entry);
+    /* since we've already parsed the policy into an addr_policy_t struct,
+     * we might not log exactly what the user typed in */
+    policy_write_item(line, TOR_ADDR_BUF_LEN + 32, p, 0);
+    log_warn(LD_DIR, "Exit policy '%s' and all following policies are "
+             "redundant, as it follows accept/reject *:* rules for both "
+             "IPv4 and IPv6. They will be removed from the exit policy. (Use "
+             "accept/reject *:* as the last entry in any exit policy.)",
+             line);
+  }
+
   if (add_default_policy) {
     append_exit_policy_string(dest, DEFAULT_EXIT_POLICY);
   } else {