Report IPv4 and IPv6 addresses resolved for each host

Previously, we would only request IPv4 addresses by default, or only
IPv6 when scanning with -6. Now, we'll request both (by not passing an
address family in the hints to getaddrinfo) and report them all in the
"Other addresses" line. This should encourage more users to scan with
-6. Additionally, it allows us to catch and report attempts to scan
IPv6-only hosts via IPv4, where previously we would just say "Failed to
resolve"

Closes #76

TargetGroup.cc

@@ -294,10 +294,20 @@ NetBlock *NetBlock::parse_expr(const char *target_expr, int af) {
  return NULL;
 }
 
+/* Returns the first address which matches the address family af */
+static const struct sockaddr_storage *first_af_address(const std::list<struct sockaddr_storage> *addrs, int af) {
+ for (std::list<struct sockaddr_storage>::const_iterator it = addrs->begin(), end = addrs->end(); it != end; ++it) {
+ if (it->ss_family == af) {
+ return &*it;
+ }
+ }
+ return NULL;
+}
+
 bool NetBlock::is_resolved_address(const struct sockaddr_storage *ss) const {
  if (this->resolvedaddrs.empty())
  return false;
- return sockaddr_storage_equal(&*this->resolvedaddrs.begin(), ss);
+ return sockaddr_storage_equal(first_af_address(&this->resolvedaddrs, ss->ss_family), ss);
 }
 
 NetBlockIPv4Ranges::NetBlockIPv4Ranges() {
@@ -610,10 +620,11 @@ NetBlock *NetBlockHostname::resolve() const {
  struct addrinfo *addrs, *addr;
  std::list<struct sockaddr_storage> resolvedaddrs;
  NetBlock *netblock;
+ const struct sockaddr_storage *sp = NULL;
  struct sockaddr_storage ss;
  size_t sslen;
 
- addrs = resolve_all(this->hostname.c_str(), this->af);
+ addrs = resolve_all(this->hostname.c_str(), AF_UNSPEC);
  for (addr = addrs; addr != NULL; addr = addr->ai_next) {
  if (addr->ai_addrlen < sizeof(ss)) {
  memcpy(&ss, addr->ai_addr, addr->ai_addrlen);
@@ -626,7 +637,22 @@ NetBlock *NetBlockHostname::resolve() const {
  if (resolvedaddrs.empty())
  return NULL;
 
- ss = *resolvedaddrs.begin();
+ sp = first_af_address(&resolvedaddrs, this->af);
+ if (sp == NULL or sp->ss_family != this->af) {
+ switch (this->af) {
+ case AF_INET:
+ error("Warning: Hostname %s resolves, but not to any IPv4 address. Try scanning with -6", this->hostname.c_str());
+ break;
+ case AF_INET6:
+ error("Warning: Hostname %s resolves, but not to any IPv6 address. Try scanning without -6", this->hostname.c_str());
+ break;
+ default:
+ error("Warning: Unknown address family: %d", this->af);
+ break;
+ }
+ return NULL;
+ }
+ ss = *sp;
  sslen = sizeof(ss);
 
  if (resolvedaddrs.size() > 1 && o.verbose > 1) {

output.cc

@@ -1426,14 +1426,17 @@ void write_host_header(Target *currenths) {
  write_host_status(currenths);
  if (currenths->TargetName() != NULL
  && currenths->resolved_addrs.size() > 1) {
- std::list<struct sockaddr_storage>::iterator it;
+ const struct sockaddr_storage *hs_ss = currenths->TargetSockAddr();
 
  log_write(LOG_PLAIN, "Other addresses for %s (not scanned):",
  currenths->TargetName());
- it = currenths->resolved_addrs.begin();
- it++;
- for (; it != currenths->resolved_addrs.end(); it++)
- log_write(LOG_PLAIN, " %s", inet_ntop_ez(&*it, sizeof(*it)));
+ for (std::list<struct sockaddr_storage>::const_iterator it = currenths->resolved_addrs.begin(), end = currenths->resolved_addrs.end();
+ it != end; it++) {
+ struct sockaddr_storage ss = *it;
+ if (!sockaddr_storage_equal(&ss, hs_ss)) {
+ log_write(LOG_PLAIN, " %s", inet_ntop_ez(&ss, sizeof(ss)));
+ }
+ }
  log_write(LOG_PLAIN, "\n");
  }
  /* Print reverse DNS if it differs. */