nss_util.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 "crypto/nss_util.h"
#include "crypto/nss_util_internal.h"

#include <nss.h>
#include <pk11pub.h>
#include <plarena.h>
#include <prerror.h>
#include <prinit.h>
#include <prtime.h>
#include <secmod.h>

#if defined(OS_LINUX)
#include <linux/nfs_fs.h>
#include <sys/vfs.h>
#elif defined(OS_OPENBSD)
#include <sys/mount.h>
#include <sys/param.h>
#endif

#include <vector>

#include "base/debug/alias.h"
#include "base/debug/stack_trace.h"
#include "base/environment.h"
#include "base/file_util.h"
#include "base/files/file_path.h"
#include "base/files/scoped_temp_dir.h"
#include "base/lazy_instance.h"
#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/metrics/histogram.h"
#include "base/native_library.h"
#include "base/strings/stringprintf.h"
#include "base/threading/thread_checker.h"
#include "base/threading/thread_restrictions.h"
#include "build/build_config.h"

// USE_NSS means we use NSS for everything crypto-related.  If USE_NSS is not
// defined, such as on Mac and Windows, we use NSS for SSL only -- we don't
// use NSS for crypto or certificate verification, and we don't use the NSS
// certificate and key databases.
#if defined(USE_NSS)
#include "base/synchronization/lock.h"
#include "crypto/crypto_module_blocking_password_delegate.h"
#endif  // defined(USE_NSS)

namespace crypto {

namespace {

#if defined(OS_CHROMEOS)
const char kNSSDatabaseName[] = "Real NSS database";

// Constants for loading the Chrome OS TPM-backed PKCS #11 library.
const char kChapsModuleName[] = "Chaps";
const char kChapsPath[] = "libchaps.so";

// Fake certificate authority database used for testing.
static const base::FilePath::CharType kReadOnlyCertDB[] =
    FILE_PATH_LITERAL("/etc/fake_root_ca/nssdb");
#endif  // defined(OS_CHROMEOS)

std::string GetNSSErrorMessage() {
  std::string result;
  if (PR_GetErrorTextLength()) {
    scoped_ptr<char[]> error_text(new char[PR_GetErrorTextLength() + 1]);
    PRInt32 copied = PR_GetErrorText(error_text.get());
    result = std::string(error_text.get(), copied);
  } else {
    result = base::StringPrintf("NSS error code: %d", PR_GetError());
  }
  return result;
}

#if defined(USE_NSS)
base::FilePath GetDefaultConfigDirectory() {
  base::FilePath dir = file_util::GetHomeDir();
  if (dir.empty()) {
    LOG(ERROR) << "Failed to get home directory.";
    return dir;
  }
  dir = dir.AppendASCII(".pki").AppendASCII("nssdb");
  if (!file_util::CreateDirectory(dir)) {
    LOG(ERROR) << "Failed to create " << dir.value() << " directory.";
    dir.clear();
  }
  return dir;
}

// On non-Chrome OS platforms, return the default config directory. On Chrome OS
// test images, return a read-only directory with fake root CA certs (which are
// used by the local Google Accounts server mock we use when testing our login
// code). On Chrome OS non-test images (where the read-only directory doesn't
// exist), return an empty path.
base::FilePath GetInitialConfigDirectory() {
#if defined(OS_CHROMEOS)
  base::FilePath database_dir = base::FilePath(kReadOnlyCertDB);
  if (!base::PathExists(database_dir))
    database_dir.clear();
  return database_dir;
#else
  return GetDefaultConfigDirectory();
#endif  // defined(OS_CHROMEOS)
}

// This callback for NSS forwards all requests to a caller-specified
// CryptoModuleBlockingPasswordDelegate object.
char* PKCS11PasswordFunc(PK11SlotInfo* slot, PRBool retry, void* arg) {
  crypto::CryptoModuleBlockingPasswordDelegate* delegate =
      reinterpret_cast<crypto::CryptoModuleBlockingPasswordDelegate*>(arg);
  if (delegate) {
    bool cancelled = false;
    std::string password = delegate->RequestPassword(PK11_GetTokenName(slot),
                                                     retry != PR_FALSE,
                                                     &cancelled);
    if (cancelled)
      return NULL;
    char* result = PORT_Strdup(password.c_str());
    password.replace(0, password.size(), password.size(), 0);
    return result;
  }
  DLOG(ERROR) << "PK11 password requested with NULL arg";
  return NULL;
}

// NSS creates a local cache of the sqlite database if it detects that the
// filesystem the database is on is much slower than the local disk.  The
// detection doesn't work with the latest versions of sqlite, such as 3.6.22
// (NSS bug https://bugzilla.mozilla.org/show_bug.cgi?id=578561).  So we set
// the NSS environment variable NSS_SDB_USE_CACHE to "yes" to override NSS's
// detection when database_dir is on NFS.  See http://crbug.com/48585.
//
// TODO(wtc): port this function to other USE_NSS platforms.  It is defined
// only for OS_LINUX and OS_OPENBSD simply because the statfs structure
// is OS-specific.
//
// Because this function sets an environment variable it must be run before we
// go multi-threaded.
void UseLocalCacheOfNSSDatabaseIfNFS(const base::FilePath& database_dir) {
#if defined(OS_LINUX) || defined(OS_OPENBSD)
  struct statfs buf;
  if (statfs(database_dir.value().c_str(), &buf) == 0) {
#if defined(OS_LINUX)
    if (buf.f_type == NFS_SUPER_MAGIC) {
#elif defined(OS_OPENBSD)
    if (strcmp(buf.f_fstypename, MOUNT_NFS) == 0) {
#endif
      scoped_ptr<base::Environment> env(base::Environment::Create());
      const char* use_cache_env_var = "NSS_SDB_USE_CACHE";
      if (!env->HasVar(use_cache_env_var))
        env->SetVar(use_cache_env_var, "yes");
    }
  }
#endif  // defined(OS_LINUX) || defined(OS_OPENBSD)
}

#endif  // defined(USE_NSS)

// A singleton to initialize/deinitialize NSPR.
// Separate from the NSS singleton because we initialize NSPR on the UI thread.
// Now that we're leaking the singleton, we could merge back with the NSS
// singleton.
class NSPRInitSingleton {
 private:
  friend struct base::DefaultLazyInstanceTraits<NSPRInitSingleton>;

  NSPRInitSingleton() {
    PR_Init(PR_USER_THREAD, PR_PRIORITY_NORMAL, 0);
  }

  // NOTE(willchan): We don't actually execute this code since we leak NSS to
  // prevent non-joinable threads from using NSS after it's already been shut
  // down.
  ~NSPRInitSingleton() {
    PL_ArenaFinish();
    PRStatus prstatus = PR_Cleanup();
    if (prstatus != PR_SUCCESS)
      LOG(ERROR) << "PR_Cleanup failed; was NSPR initialized on wrong thread?";
  }
};

base::LazyInstance<NSPRInitSingleton>::Leaky
    g_nspr_singleton = LAZY_INSTANCE_INITIALIZER;

// This is a LazyInstance so that it will be deleted automatically when the
// unittest exits.  NSSInitSingleton is a LeakySingleton, so it would not be
// deleted if it were a regular member.
base::LazyInstance<base::ScopedTempDir> g_test_nss_db_dir =
    LAZY_INSTANCE_INITIALIZER;

// Force a crash with error info on NSS_NoDB_Init failure.
void CrashOnNSSInitFailure() {
  int nss_error = PR_GetError();
  int os_error = PR_GetOSError();
  base::debug::Alias(&nss_error);
  base::debug::Alias(&os_error);
  LOG(ERROR) << "Error initializing NSS without a persistent database: "
             << GetNSSErrorMessage();
  LOG(FATAL) << "nss_error=" << nss_error << ", os_error=" << os_error;
}

class NSSInitSingleton {
 public:
#if defined(OS_CHROMEOS)
  void OpenPersistentNSSDB() {
    DCHECK(thread_checker_.CalledOnValidThread());

    if (!chromeos_user_logged_in_) {
      // GetDefaultConfigDirectory causes us to do blocking IO on UI thread.
      // Temporarily allow it until we fix http://crbug.com/70119
      base::ThreadRestrictions::ScopedAllowIO allow_io;
      chromeos_user_logged_in_ = true;

      // This creates another DB slot in NSS that is read/write, unlike
      // the fake root CA cert DB and the "default" crypto key
      // provider, which are still read-only (because we initialized
      // NSS before we had a cryptohome mounted).
      software_slot_ = OpenUserDB(GetDefaultConfigDirectory(),
                                  kNSSDatabaseName);
    }
  }

  void EnableTPMTokenForNSS() {
    DCHECK(thread_checker_.CalledOnValidThread());

    // If this gets set, then we'll use the TPM for certs with
    // private keys, otherwise we'll fall back to the software
    // implementation.
    tpm_token_enabled_for_nss_ = true;
  }

  bool InitializeTPMToken(const std::string& token_name,
                          int token_slot_id,
                          const std::string& user_pin) {
    DCHECK(thread_checker_.CalledOnValidThread());

    // If EnableTPMTokenForNSS hasn't been called, return false.
    if (!tpm_token_enabled_for_nss_)
      return false;

    // If everything is already initialized, then return true.
    if (chaps_module_ && tpm_slot_)
      return true;

    tpm_token_name_ = token_name;
    tpm_user_pin_ = user_pin;

    // This tries to load the Chaps module so NSS can talk to the hardware
    // TPM.
    if (!chaps_module_) {
      chaps_module_ = LoadModule(
          kChapsModuleName,
          kChapsPath,
          // For more details on these parameters, see:
          // https://developer.mozilla.org/en/PKCS11_Module_Specs
          // slotFlags=[PublicCerts] -- Certificates and public keys can be
          //   read from this slot without requiring a call to C_Login.
          // askpw=only -- Only authenticate to the token when necessary.
          "NSS=\"slotParams=(0={slotFlags=[PublicCerts] askpw=only})\"");
      if (!chaps_module_ && test_slot_) {
        // chromeos_unittests try to test the TPM initialization process. If we
        // have a test DB open, pretend that it is the TPM slot.
        tpm_slot_ = PK11_ReferenceSlot(test_slot_);
        return true;
      }
    }
    if (chaps_module_){
      tpm_slot_ = GetTPMSlotForId(token_slot_id);

      return tpm_slot_ != NULL;
    }
    return false;
  }

  void GetTPMTokenInfo(std::string* token_name, std::string* user_pin) {
    DCHECK(thread_checker_.CalledOnValidThread());
    if (!tpm_token_enabled_for_nss_) {
      LOG(ERROR) << "GetTPMTokenInfo called before TPM Token is ready.";
      return;
    }
    if (token_name)
      *token_name = tpm_token_name_;
    if (user_pin)
      *user_pin = tpm_user_pin_;
  }

  bool IsTPMTokenReady() {
    // TODO(mattm): Change to DCHECK when callers have been fixed.
    if (!thread_checker_.CalledOnValidThread()) {
      DVLOG(1) << "Called on wrong thread.\n"
               << base::debug::StackTrace().ToString();
    }

    return tpm_slot_ != NULL;
  }

  // Note that CK_SLOT_ID is an unsigned long, but cryptohome gives us the slot
  // id as an int. This should be safe since this is only used with chaps, which
  // we also control.
  PK11SlotInfo* GetTPMSlotForId(CK_SLOT_ID slot_id) {
    DCHECK(thread_checker_.CalledOnValidThread());

    if (!chaps_module_)
      return NULL;

    VLOG(1) << "Poking chaps module.";
    SECStatus rv = SECMOD_UpdateSlotList(chaps_module_);
    if (rv != SECSuccess)
      PLOG(ERROR) << "SECMOD_UpdateSlotList failed: " << PORT_GetError();

    PK11SlotInfo* slot = SECMOD_LookupSlot(chaps_module_->moduleID, slot_id);
    if (!slot)
      LOG(ERROR) << "TPM slot " << slot_id << " not found.";
    return slot;
  }
#endif  // defined(OS_CHROMEOS)


  bool OpenTestNSSDB() {
    DCHECK(thread_checker_.CalledOnValidThread());

    if (test_slot_)
      return true;
    if (!g_test_nss_db_dir.Get().CreateUniqueTempDir())
      return false;
    test_slot_ = OpenUserDB(g_test_nss_db_dir.Get().path(), kTestTPMTokenName);
    return !!test_slot_;
  }

  void CloseTestNSSDB() {
    DCHECK(thread_checker_.CalledOnValidThread());

    if (!test_slot_)
      return;
    SECStatus status = SECMOD_CloseUserDB(test_slot_);
    if (status != SECSuccess)
      PLOG(ERROR) << "SECMOD_CloseUserDB failed: " << PORT_GetError();
    PK11_FreeSlot(test_slot_);
    test_slot_ = NULL;
    ignore_result(g_test_nss_db_dir.Get().Delete());
  }

  PK11SlotInfo* GetPublicNSSKeySlot() {
    // TODO(mattm): Change to DCHECK when callers have been fixed.
    if (!thread_checker_.CalledOnValidThread()) {
      DVLOG(1) << "Called on wrong thread.\n"
               << base::debug::StackTrace().ToString();
    }

    if (test_slot_)
      return PK11_ReferenceSlot(test_slot_);
    if (software_slot_)
      return PK11_ReferenceSlot(software_slot_);
    return PK11_GetInternalKeySlot();
  }

  PK11SlotInfo* GetPrivateNSSKeySlot() {
    // TODO(mattm): Change to DCHECK when callers have been fixed.
    if (!thread_checker_.CalledOnValidThread()) {
      DVLOG(1) << "Called on wrong thread.\n"
               << base::debug::StackTrace().ToString();
    }

    if (test_slot_)
      return PK11_ReferenceSlot(test_slot_);

#if defined(OS_CHROMEOS)
    if (tpm_token_enabled_for_nss_) {
      if (IsTPMTokenReady()) {
        return PK11_ReferenceSlot(tpm_slot_);
      } else {
        // If we were supposed to get the hardware token, but were
        // unable to, return NULL rather than fall back to sofware.
        return NULL;
      }
    }
#endif
    // If we weren't supposed to enable the TPM for NSS, then return
    // the software slot.
    if (software_slot_)
      return PK11_ReferenceSlot(software_slot_);
    return PK11_GetInternalKeySlot();
  }

#if defined(USE_NSS)
  base::Lock* write_lock() {
    return &write_lock_;
  }
#endif  // defined(USE_NSS)

  // This method is used to force NSS to be initialized without a DB.
  // Call this method before NSSInitSingleton() is constructed.
  static void ForceNoDBInit() {
    force_nodb_init_ = true;
  }

 private:
  friend struct base::DefaultLazyInstanceTraits<NSSInitSingleton>;

  NSSInitSingleton()
      : tpm_token_enabled_for_nss_(false),
        chaps_module_(NULL),
        software_slot_(NULL),
        test_slot_(NULL),
        tpm_slot_(NULL),
        root_(NULL),
        chromeos_user_logged_in_(false) {
    base::TimeTicks start_time = base::TimeTicks::Now();

    // It's safe to construct on any thread, since LazyInstance will prevent any
    // other threads from accessing until the constructor is done.
    thread_checker_.DetachFromThread();

    EnsureNSPRInit();

    // We *must* have NSS >= 3.14.3.
    COMPILE_ASSERT(
        (NSS_VMAJOR == 3 && NSS_VMINOR == 14 && NSS_VPATCH >= 3) ||
        (NSS_VMAJOR == 3 && NSS_VMINOR > 14) ||
        (NSS_VMAJOR > 3),
        nss_version_check_failed);
    // Also check the run-time NSS version.
    // NSS_VersionCheck is a >= check, not strict equality.
    if (!NSS_VersionCheck("3.14.3")) {
      LOG(FATAL) << "NSS_VersionCheck(\"3.14.3\") failed. NSS >= 3.14.3 is "
                    "required. Please upgrade to the latest NSS, and if you "
                    "still get this error, contact your distribution "
                    "maintainer.";
    }

    SECStatus status = SECFailure;
    bool nodb_init = force_nodb_init_;

#if !defined(USE_NSS)
    // Use the system certificate store, so initialize NSS without database.
    nodb_init = true;
#endif

    if (nodb_init) {
      status = NSS_NoDB_Init(NULL);
      if (status != SECSuccess) {
        CrashOnNSSInitFailure();
        return;
      }
#if defined(OS_IOS)
      root_ = InitDefaultRootCerts();
#endif  // defined(OS_IOS)
    } else {
#if defined(USE_NSS)
      base::FilePath database_dir = GetInitialConfigDirectory();
      if (!database_dir.empty()) {
        // This duplicates the work which should have been done in
        // EarlySetupForNSSInit. However, this function is idempotent so
        // there's no harm done.
        UseLocalCacheOfNSSDatabaseIfNFS(database_dir);

        // Initialize with a persistent database (likely, ~/.pki/nssdb).
        // Use "sql:" which can be shared by multiple processes safely.
        std::string nss_config_dir =
            base::StringPrintf("sql:%s", database_dir.value().c_str());
#if defined(OS_CHROMEOS)
        status = NSS_Init(nss_config_dir.c_str());
#else
        status = NSS_InitReadWrite(nss_config_dir.c_str());
#endif
        if (status != SECSuccess) {
          LOG(ERROR) << "Error initializing NSS with a persistent "
                        "database (" << nss_config_dir
                     << "): " << GetNSSErrorMessage();
        }
      }
      if (status != SECSuccess) {
        VLOG(1) << "Initializing NSS without a persistent database.";
        status = NSS_NoDB_Init(NULL);
        if (status != SECSuccess) {
          CrashOnNSSInitFailure();
          return;
        }
      }

      PK11_SetPasswordFunc(PKCS11PasswordFunc);

      // If we haven't initialized the password for the NSS databases,
      // initialize an empty-string password so that we don't need to
      // log in.
      PK11SlotInfo* slot = PK11_GetInternalKeySlot();
      if (slot) {
        // PK11_InitPin may write to the keyDB, but no other thread can use NSS
        // yet, so we don't need to lock.
        if (PK11_NeedUserInit(slot))
          PK11_InitPin(slot, NULL, NULL);
        PK11_FreeSlot(slot);
      }

      root_ = InitDefaultRootCerts();
#endif  // defined(USE_NSS)
    }

    // Disable MD5 certificate signatures. (They are disabled by default in
    // NSS 3.14.)
    NSS_SetAlgorithmPolicy(SEC_OID_MD5, 0, NSS_USE_ALG_IN_CERT_SIGNATURE);
    NSS_SetAlgorithmPolicy(SEC_OID_PKCS1_MD5_WITH_RSA_ENCRYPTION,
                           0, NSS_USE_ALG_IN_CERT_SIGNATURE);

    // The UMA bit is conditionally set for this histogram in
    // chrome/common/startup_metric_utils.cc .
    HISTOGRAM_CUSTOM_TIMES("Startup.SlowStartupNSSInit",
                           base::TimeTicks::Now() - start_time,
                           base::TimeDelta::FromMilliseconds(10),
                           base::TimeDelta::FromHours(1),
                           50);
  }

  // NOTE(willchan): We don't actually execute this code since we leak NSS to
  // prevent non-joinable threads from using NSS after it's already been shut
  // down.
  ~NSSInitSingleton() {
    if (tpm_slot_) {
      PK11_FreeSlot(tpm_slot_);
      tpm_slot_ = NULL;
    }
    if (software_slot_) {
      SECMOD_CloseUserDB(software_slot_);
      PK11_FreeSlot(software_slot_);
      software_slot_ = NULL;
    }
    CloseTestNSSDB();
    if (root_) {
      SECMOD_UnloadUserModule(root_);
      SECMOD_DestroyModule(root_);
      root_ = NULL;
    }
    if (chaps_module_) {
      SECMOD_UnloadUserModule(chaps_module_);
      SECMOD_DestroyModule(chaps_module_);
      chaps_module_ = NULL;
    }

    SECStatus status = NSS_Shutdown();
    if (status != SECSuccess) {
      // We VLOG(1) because this failure is relatively harmless (leaking, but
      // we're shutting down anyway).
      VLOG(1) << "NSS_Shutdown failed; see http://crbug.com/4609";
    }
  }

#if defined(USE_NSS) || defined(OS_IOS)
  // Load nss's built-in root certs.
  SECMODModule* InitDefaultRootCerts() {
    SECMODModule* root = LoadModule("Root Certs", "libnssckbi.so", NULL);
    if (root)
      return root;

    // Aw, snap.  Can't find/load root cert shared library.
    // This will make it hard to talk to anybody via https.
    // TODO(mattm): Re-add the NOTREACHED here when crbug.com/310972 is fixed.
    return NULL;
  }

  // Load the given module for this NSS session.
  SECMODModule* LoadModule(const char* name,
                           const char* library_path,
                           const char* params) {
    std::string modparams = base::StringPrintf(
        "name=\"%s\" library=\"%s\" %s",
        name, library_path, params ? params : "");

    // Shouldn't need to const_cast here, but SECMOD doesn't properly
    // declare input string arguments as const.  Bug
    // https://bugzilla.mozilla.org/show_bug.cgi?id=642546 was filed
    // on NSS codebase to address this.
    SECMODModule* module = SECMOD_LoadUserModule(
        const_cast<char*>(modparams.c_str()), NULL, PR_FALSE);
    if (!module) {
      LOG(ERROR) << "Error loading " << name << " module into NSS: "
                 << GetNSSErrorMessage();
      return NULL;
    }
    if (!module->loaded) {
      LOG(ERROR) << "After loading " << name << ", loaded==false: "
                 << GetNSSErrorMessage();
      SECMOD_DestroyModule(module);
      return NULL;
    }
    return module;
  }
#endif

  static PK11SlotInfo* OpenUserDB(const base::FilePath& path,
                                  const char* description) {
    const std::string modspec =
        base::StringPrintf("configDir='sql:%s' tokenDescription='%s'",
                           path.value().c_str(), description);
    PK11SlotInfo* db_slot = SECMOD_OpenUserDB(modspec.c_str());
    if (db_slot) {
      if (PK11_NeedUserInit(db_slot))
        PK11_InitPin(db_slot, NULL, NULL);
    }
    else {
      LOG(ERROR) << "Error opening persistent database (" << modspec
                 << "): " << GetNSSErrorMessage();
    }
    return db_slot;
  }

  // If this is set to true NSS is forced to be initialized without a DB.
  static bool force_nodb_init_;

  bool tpm_token_enabled_for_nss_;
  std::string tpm_token_name_;
  std::string tpm_user_pin_;
  SECMODModule* chaps_module_;
  PK11SlotInfo* software_slot_;
  PK11SlotInfo* test_slot_;
  PK11SlotInfo* tpm_slot_;
  SECMODModule* root_;
  bool chromeos_user_logged_in_;
#if defined(USE_NSS)
  // TODO(davidben): When https://bugzilla.mozilla.org/show_bug.cgi?id=564011
  // is fixed, we will no longer need the lock.
  base::Lock write_lock_;
#endif  // defined(USE_NSS)

  base::ThreadChecker thread_checker_;
};

// static
bool NSSInitSingleton::force_nodb_init_ = false;

base::LazyInstance<NSSInitSingleton>::Leaky
    g_nss_singleton = LAZY_INSTANCE_INITIALIZER;
}  // namespace

const char kTestTPMTokenName[] = "Test DB";

#if defined(USE_NSS)
void EarlySetupForNSSInit() {
  base::FilePath database_dir = GetInitialConfigDirectory();
  if (!database_dir.empty())
    UseLocalCacheOfNSSDatabaseIfNFS(database_dir);
}
#endif

void EnsureNSPRInit() {
  g_nspr_singleton.Get();
}

void InitNSSSafely() {
  // We might fork, but we haven't loaded any security modules.
  DisableNSSForkCheck();
  // If we're sandboxed, we shouldn't be able to open user security modules,
  // but it's more correct to tell NSS to not even try.
  // Loading user security modules would have security implications.
  ForceNSSNoDBInit();
  // Initialize NSS.
  EnsureNSSInit();
}

void EnsureNSSInit() {
  // Initializing SSL causes us to do blocking IO.
  // Temporarily allow it until we fix
  //   http://code.google.com/p/chromium/issues/detail?id=59847
  base::ThreadRestrictions::ScopedAllowIO allow_io;
  g_nss_singleton.Get();
}

void ForceNSSNoDBInit() {
  NSSInitSingleton::ForceNoDBInit();
}

void DisableNSSForkCheck() {
  scoped_ptr<base::Environment> env(base::Environment::Create());
  env->SetVar("NSS_STRICT_NOFORK", "DISABLED");
}

void LoadNSSLibraries() {
  // Some NSS libraries are linked dynamically so load them here.
#if defined(USE_NSS)
  // Try to search for multiple directories to load the libraries.
  std::vector<base::FilePath> paths;

  // Use relative path to Search PATH for the library files.
  paths.push_back(base::FilePath());

  // For Debian derivatives NSS libraries are located here.
  paths.push_back(base::FilePath("/usr/lib/nss"));

  // Ubuntu 11.10 (Oneiric) and Debian Wheezy place the libraries here.
#if defined(ARCH_CPU_X86_64)
  paths.push_back(base::FilePath("/usr/lib/x86_64-linux-gnu/nss"));
#elif defined(ARCH_CPU_X86)
  paths.push_back(base::FilePath("/usr/lib/i386-linux-gnu/nss"));
#elif defined(ARCH_CPU_ARMEL)
  paths.push_back(base::FilePath("/usr/lib/arm-linux-gnueabi/nss"));
#elif defined(ARCH_CPU_MIPSEL)
  paths.push_back(base::FilePath("/usr/lib/mipsel-linux-gnu/nss"));
#endif

  // A list of library files to load.
  std::vector<std::string> libs;
  libs.push_back("libsoftokn3.so");
  libs.push_back("libfreebl3.so");

  // For each combination of library file and path, check for existence and
  // then load.
  size_t loaded = 0;
  for (size_t i = 0; i < libs.size(); ++i) {
    for (size_t j = 0; j < paths.size(); ++j) {
      base::FilePath path = paths[j].Append(libs[i]);
      base::NativeLibrary lib = base::LoadNativeLibrary(path, NULL);
      if (lib) {
        ++loaded;
        break;
      }
    }
  }

  if (loaded == libs.size()) {
    VLOG(3) << "NSS libraries loaded.";
  } else {
    LOG(ERROR) << "Failed to load NSS libraries.";
  }
#endif
}

bool CheckNSSVersion(const char* version) {
  return !!NSS_VersionCheck(version);
}

#if defined(USE_NSS)
ScopedTestNSSDB::ScopedTestNSSDB()
  : is_open_(g_nss_singleton.Get().OpenTestNSSDB()) {
}

ScopedTestNSSDB::~ScopedTestNSSDB() {
  // Don't close when NSS is < 3.15.1, because it would require an additional
  // sleep for 1 second after closing the database, due to
  // http://bugzil.la/875601.
  if (NSS_VersionCheck("3.15.1")) {
    g_nss_singleton.Get().CloseTestNSSDB();
  }
}

base::Lock* GetNSSWriteLock() {
  return g_nss_singleton.Get().write_lock();
}

AutoNSSWriteLock::AutoNSSWriteLock() : lock_(GetNSSWriteLock()) {
  // May be NULL if the lock is not needed in our version of NSS.
  if (lock_)
    lock_->Acquire();
}

AutoNSSWriteLock::~AutoNSSWriteLock() {
  if (lock_) {
    lock_->AssertAcquired();
    lock_->Release();
  }
}

AutoSECMODListReadLock::AutoSECMODListReadLock()
      : lock_(SECMOD_GetDefaultModuleListLock()) {
    SECMOD_GetReadLock(lock_);
  }

AutoSECMODListReadLock::~AutoSECMODListReadLock() {
  SECMOD_ReleaseReadLock(lock_);
}

#endif  // defined(USE_NSS)

#if defined(OS_CHROMEOS)
void OpenPersistentNSSDB() {
  g_nss_singleton.Get().OpenPersistentNSSDB();
}

void EnableTPMTokenForNSS() {
  g_nss_singleton.Get().EnableTPMTokenForNSS();
}

void GetTPMTokenInfo(std::string* token_name, std::string* user_pin) {
  g_nss_singleton.Get().GetTPMTokenInfo(token_name, user_pin);
}

bool IsTPMTokenReady() {
  return g_nss_singleton.Get().IsTPMTokenReady();
}

bool InitializeTPMToken(const std::string& token_name,
                        int token_slot_id,
                        const std::string& user_pin) {
  return g_nss_singleton.Get().InitializeTPMToken(
      token_name, token_slot_id, user_pin);
}
#endif  // defined(OS_CHROMEOS)

base::Time PRTimeToBaseTime(PRTime prtime) {
  return base::Time::FromInternalValue(
      prtime + base::Time::UnixEpoch().ToInternalValue());
}

PRTime BaseTimeToPRTime(base::Time time) {
  return time.ToInternalValue() - base::Time::UnixEpoch().ToInternalValue();
}

PK11SlotInfo* GetPublicNSSKeySlot() {
  return g_nss_singleton.Get().GetPublicNSSKeySlot();
}

PK11SlotInfo* GetPrivateNSSKeySlot() {
  return g_nss_singleton.Get().GetPrivateNSSKeySlot();
}

}  // namespace crypto