Ensure native library isn't actually loaded, and no IO on net thread

net/udp/udp_socket_posix.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/udp/udp_socket_posix.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <net/if.h>
 #include <netdb.h>
@@ skipping 14 matching lines @@
 #include "net/base/ip_address.h"
 #include "net/base/ip_endpoint.h"
 #include "net/base/net_errors.h"
 #include "net/base/network_activity_monitor.h"
 #include "net/base/sockaddr_storage.h"
 #include "net/log/net_log.h"
 #include "net/socket/socket_descriptor.h"
 #include "net/udp/udp_net_log_parameters.h"
 
 #if defined(OS_ANDROID)
+#include <dlfcn.h>
+// This was added in Lollipop to dlfcn.h
+#define RTLD_NOLOAD 4
 #include "base/android/build_info.h"
 #include "base/native_library.h"
 #include "base/strings/utf_string_conversions.h"
 #endif
 
 namespace net {
 
 namespace {
 
 const int kBindRetries = 10;
@@ skipping 299 matching lines @@
     return ERR_NOT_IMPLEMENTED;
   }
   // NOTE(pauljensen): This does rely on Android implementation details, but
   // these details are unlikely to change.
   typedef int (*SetNetworkForSocket)(unsigned netId, int socketFd);
   static SetNetworkForSocket setNetworkForSocket;
   // This is racy, but all racers should come out with the same answer so it
   // shouldn't matter.
   if (!setNetworkForSocket) {
     // Android's netd client library should always be loaded in our address
-    // space as it shims libc functions like connect().
+    // space as it shims socket() which was used to create |socket_|.
     base::FilePath file(base::GetNativeLibraryName("netd_client"));
-    base::NativeLibrary lib = base::LoadNativeLibrary(file, nullptr);
-    setNetworkForSocket = reinterpret_cast<SetNetworkForSocket>(
-        base::GetFunctionPointerFromNativeLibrary(lib, "setNetworkForSocket"));
+    // Use RTLD_NOW to match Android's prior loading of the library:
+    // http://androidxref.com/6.0.0_r5/xref/bionic/libc/bionic/NetdClient.cpp#37
+    // Use RTLD_NOLOAD to assert that the library is already loaded and
+    // avoid doing any disk IO.
+    void* dl = dlopen(file.value().c_str(), RTLD_NOW | RTLD_NOLOAD);
+    setNetworkForSocket =
+        reinterpret_cast<SetNetworkForSocket>(dlsym(dl, "setNetworkForSocket"));
   }
   if (!setNetworkForSocket)
     return ERR_NOT_IMPLEMENTED;
   int rv = setNetworkForSocket(network, socket_);
   // If |network| has since disconnected, |rv| will be ENONET.  Surface this as
   // ERR_NETWORK_CHANGED, rather than MapSystemError(ENONET) which gives back
   // the less descriptive ERR_FAILED.
   if (rv == ENONET)
     return ERR_NETWORK_CHANGED;
   if (rv == 0)
@@ skipping 437 matching lines @@
     return MapSystemError(errno);
 
   return OK;
 }
 
 void UDPSocketPosix::DetachFromThread() {
   base::NonThreadSafe::DetachFromThread();
 }
 
 }  // namespace net