[net] Adds AddressTrackerLinux which keeps track of interface addresses using rtnetlink.

net/base/address_tracker_linux.cc

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/base/address_tracker_linux.h"
+
+#include <errno.h>
+
+#include "base/eintr_wrapper.h"
+#include "base/logging.h"
+#include "net/base/network_change_notifier_linux.h"
+
+namespace net {
+namespace internal {
+
+namespace {
+
+// Retrieves address from NETLINK address message.
+bool GetAddress(const struct nlmsghdr* header, IPAddressNumber* out) {
+  const struct ifaddrmsg* msg =
+      reinterpret_cast<struct ifaddrmsg*>(NLMSG_DATA(header));
+  size_t address_length = 0;
+  switch (msg->ifa_family) {
+    case AF_INET:
+      address_length = kIPv4AddressSize;
+      break;
+    case AF_INET6:
+      address_length = kIPv6AddressSize;
+      break;
+    default:
+      // Unknown family.
+      return false;
+  }
+  size_t length = IFA_PAYLOAD(header);
+  const struct rtattr* attr = reinterpret_cast<struct rtattr*>(IFA_RTA(msg));
+  unsigned char* address = NULL;
+  unsigned char* local = NULL;
+  for (; RTA_OK(attr, length); attr = RTA_NEXT(attr, length)) {
+    switch (attr->rta_type) {
+      case IFA_ADDRESS:
+        local = reinterpret_cast<unsigned char*>(RTA_DATA(attr));
+        break;
+      case IFA_LOCAL:
+        address = reinterpret_cast<unsigned char*>(RTA_DATA(attr));
+        break;
+      default:
+        break;
+    }
+  }
+  if (local)
+    address = local;
+  if (!address)
+    return false;
+  out->assign(address, address + address_length);
+  return true;
+}
+
+void CloseSocket(int fd) {
+  if (HANDLE_EINTR(close(fd)) < 0)
+    PLOG(ERROR) << "Could not close NETLINK socket.";
+}
+
+}  // namespace
+
+AddressTrackerLinux::AddressTrackerLinux() : netlink_fd_(-1) {}
+
+AddressTrackerLinux::~AddressTrackerLinux() {
+  if (netlink_fd_ >= 0)
+    CloseSocket(netlink_fd_);
+}
+
+void AddressTrackerLinux::Init() {
+  int sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+  if (sock < 0) {
+    PLOG(ERROR) << "Could not create NETLINK socket";
+    return;
+  }
+
+  // Request notifications.
+  struct sockaddr_nl addr = {};
+  addr.nl_family = AF_NETLINK;
+  addr.nl_pid = getpid();
+  // TODO(szym): Track RTMGRP_LINK as well for ifi_type
+  addr.nl_groups = RTMGRP_IPV4_IFADDR | RTMGRP_IPV6_IFADDR | RTMGRP_NOTIFY;
+  int rv = bind(sock, reinterpret_cast<struct sockaddr*>(&addr), sizeof(addr));
+  if (rv < 0) {
+    PLOG(ERROR) << "Could not bind NETLINK socket";
+    CloseSocket(sock);
+    return;
+  }
+
+  // Request dump of addresses.
+  struct sockaddr_nl peer = {};
+  peer.nl_family = AF_NETLINK;
+
+  struct {
+    struct nlmsghdr header;
+    struct rtgenmsg msg;
+  } request = {};
+
+  request.header.nlmsg_len = NLMSG_LENGTH(sizeof(request.msg));
+  request.header.nlmsg_type = RTM_GETADDR;
+  request.header.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
+  request.header.nlmsg_pid = getpid();
+  request.msg.rtgen_family = AF_UNSPEC;
+
+  rv = HANDLE_EINTR(sendto(sock, &request, request.header.nlmsg_len, 0,
+                           reinterpret_cast<struct sockaddr*>(&peer),
+                           sizeof(peer)));
+  if (rv < 0) {
+    PLOG(ERROR) << "Could not send NETLINK request";
+    CloseSocket(sock);
+    return;
+  }
+
+  // Watch for asynchronous messages.
+  if (SetNonBlocking(sock)) {
+    PLOG(ERROR) << "Could not make NETLINK socket non-blocking";
+    CloseSocket(sock);
+    return;
+  }
+
+  rv = MessageLoopForIO::current()->WatchFileDescriptor(
+      sock, true, MessageLoopForIO::WATCH_READ, &watcher_, this);
+  if (rv < 0) {
+    PLOG(ERROR) << "Could not watch NETLINK socket";
+    CloseSocket(sock);
+    return;
+  }
+
+  netlink_fd_ = sock;
+  ReadMessages();

[vandebo (ex-Chrome), 2012/06/29 17:52:03]

Do you need to call ReadMessages here?  Won't watch file descriptor call it in a
little bit?  If not (because you're racing the result), why not setup the
watcher before sending the dump request?

[szym, 2012/06/29 18:34:52]

The intention was to read all messages in response to the dump request before
calling NotifyObserversOfIPAddressChange. That said, I think it makes sense to
actually send the notification afterwards since the consumers of
AddressTrackerLinux::GetMap would like to get the info once it's complete.

I removed it from here.

+}
+
+AddressTrackerLinux::AddressMap AddressTrackerLinux::GetMap() const {
+  base::AutoLock lock(lock_);
+  return map_;
+}
+
+bool AddressTrackerLinux::ReadMessages() {
+  char buf[4096];
+  bool changed = false;
+  for (;;) {
+    int rv = HANDLE_EINTR(recv(netlink_fd_, buf, sizeof(buf), 0));
+    if (rv == 0) {
+      LOG(ERROR) << "Unexpected shutdown of NETLINK socket.";
+      return false;
+    }
+    if (rv < 0) {
+      if ((errno == EAGAIN) || (errno == EWOULDBLOCK))
+        break;
+      PLOG(ERROR) << "Failed to recv from netlink socket";
+      return false;
+    }
+    changed |= HandleMessage(buf, rv);
+  };
+  return changed;
+}
+
+bool AddressTrackerLinux::HandleMessage(char* buf, size_t len) {
+  DCHECK(buf);
+  bool changed = false;
+  const struct nlmsghdr* header = reinterpret_cast<struct nlmsghdr*>(buf);
+  for (; NLMSG_OK(header, len); header = NLMSG_NEXT(header, len)) {
+    switch (header->nlmsg_type) {

[vandebo (ex-Chrome), 2012/06/29 17:52:03]

So this logic is no worse than what we had before, but it doesn't solve the IPv6
privacy extension problem.  To address that, you'd have to compare arriving and
leaving addresses to other addresses to see if a new network is available.

[szym, 2012/06/29 18:34:52]

The goal was to filter out RTM_NEWADDR announcements which don't change the IP
address. This code will only set |changed = true| if the address is completely
new or if the ifaddrmsg content has changed. I don't think the router
announcements mentioned in http://crbug.com/100690 change ifaddrmsg.

[vandebo (ex-Chrome), 2012/06/29 21:01:18]

It's true that 100690 implies that only the time stamp is changing, but with the
privacy extension, you do get new addresses periodically and then some time
later the oldest one gets removed.  So instead of resetting the network state
every few seconds it might be every few hours.  A complete solution should
address this.

From my understanding the bottom 64bits of a IPv6 address will change for
privacy addresses, so a new address that only varies in the bottom 64bits from
an existing address shouldn't trigger a network change event.  Similarly for a
removed address.

[szym, 2012/06/29 21:09:06]

We must not simply ignore such a change. In particular, RFC3484 requires an
up-to-date information on source addresses and will need to receive an update
even if a change is due to privacy extension. I imagine there will be other
places (jingle?) which will want to know when the preferred IP address changes.
 
One solution is to add a |detail| field to OnIPAddressChanged (see OnDNSChanged)
which will be used to distinguish network changes from address changes.

+      case NLMSG_DONE:
+        return changed;
+      case NLMSG_ERROR:
+        LOG(ERROR) << "Unexpected netlink error.";
+        return changed;
+      case RTM_NEWADDR: {
+        IPAddressNumber address;
+        if (GetAddress(header, &address)) {
+          base::AutoLock lock(lock_);
+          const struct ifaddrmsg* msg =
+              reinterpret_cast<struct ifaddrmsg*>(NLMSG_DATA(header));
+          AddressMap::iterator it = map_.find(address);
+          if (it == map_.end()) {
+            map_.insert(it, std::make_pair(address, *msg));
+            changed = true;
+          } else if (memcmp(&it->second, msg, sizeof(*msg))) {
+            it->second = *msg;
+            changed = true;
+          }
+        }
+      } break;
+      case RTM_DELADDR: {
+        IPAddressNumber address;
+        if (GetAddress(header, &address)) {
+          base::AutoLock lock(lock_);
+          if (map_.erase(address))
+            changed = true;
+        }
+      } break;
+      case RTM_NEWLINK:
+      case RTM_DELLINK:
+        // TODO(szym): handle for ifi_type.
+        break;
+      default:
+        break;
+    }
+  }
+  return changed;
+}
+
+void AddressTrackerLinux::OnFileCanReadWithoutBlocking(int fd) {
+  if (ReadMessages())
+    NetworkChangeNotifierLinux::NotifyObserversOfIPAddressChange();
+}
+
+void AddressTrackerLinux::OnFileCanWriteWithoutBlocking(int /* fd */) {}
+
+}  // namespace internal
+}  // namespace net