From 0c2a5723beff39d1f62daec96b5389da3d427e79 Mon Sep 17 00:00:00 2001 From: Ben Noordhuis Date: Sun, 11 Sep 2022 10:48:34 +0200 Subject: [PATCH] crypto: fix weak randomness in WebCrypto keygen MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Commit dae283d96f from August 2020 introduced a call to EntropySource() in SecretKeyGenTraits::DoKeyGen() in src/crypto/crypto_keygen.cc. There are two problems with that: 1. It does not check the return value, it assumes EntropySource() always succeeds, but it can (and sometimes will) fail. 2. The random data returned byEntropySource() may not be cryptographically strong and therefore not suitable as keying material. An example is a freshly booted system or a system without /dev/random or getrandom(2). EntropySource() calls out to openssl's RAND_poll() and RAND_bytes() in a best-effort attempt to obtain random data. OpenSSL has a built-in CSPRNG but that can fail to initialize, in which case it's possible either: 1. No random data gets written to the output buffer, i.e., the output is unmodified, or 2. Weak random data is written. It's theoretically possible for the output to be fully predictable because the CSPRNG starts from a predictable state. Replace EntropySource() and CheckEntropy() with new function CSPRNG() that enforces checking of the return value. Abort on startup when the entropy pool fails to initialize because that makes it too easy to compromise the security of the process. Refs: https://hackerone.com/bugs?report_id=1690000 Refs: https://github.com/nodejs/node/pull/35093 Reviewed-By: Rafael Gonzaga Reviewed-By: Tobias Nießen PR-URL: #346 Backport-PR-URL: #351 CVE-ID: CVE-2022-35255 --- node.gyp | 2 ++ src/crypto/crypto_context.cc | 19 ++++++++++-------- src/crypto/crypto_keygen.cc | 8 +++++++- src/crypto/crypto_keygen.h | 3 --- src/crypto/crypto_random.cc | 15 +++++++-------- src/crypto/crypto_util.cc | 28 ++++++++------------------- src/crypto/crypto_util.h | 37 ++++++++++++------------------------ src/inspector_io.cc | 3 +-- src/node.cc | 30 ++++++++++++++++++----------- 9 files changed, 67 insertions(+), 78 deletions(-) diff --git a/node.gyp b/node.gyp index 347d82d2e1e100..8f131acf661b8e 100644 --- a/node.gyp +++ b/node.gyp @@ -683,6 +683,8 @@ 'openssl_default_cipher_list%': '', }, + 'cflags': ['-Werror=unused-result'], + 'defines': [ 'NODE_ARCH="<(target_arch)"', 'NODE_PLATFORM="<(OS)"', diff --git a/src/crypto/crypto_context.cc b/src/crypto/crypto_context.cc index 7eab9de37cb3a1..e70ddc64f3685b 100644 --- a/src/crypto/crypto_context.cc +++ b/src/crypto/crypto_context.cc @@ -541,9 +541,9 @@ void SecureContext::Init(const FunctionCallbackInfo& args) { // OpenSSL 1.1.0 changed the ticket key size, but the OpenSSL 1.0.x size was // exposed in the public API. To retain compatibility, install a callback // which restores the old algorithm. - if (RAND_bytes(sc->ticket_key_name_, sizeof(sc->ticket_key_name_)) <= 0 || - RAND_bytes(sc->ticket_key_hmac_, sizeof(sc->ticket_key_hmac_)) <= 0 || - RAND_bytes(sc->ticket_key_aes_, sizeof(sc->ticket_key_aes_)) <= 0) { + if (CSPRNG(sc->ticket_key_name_, sizeof(sc->ticket_key_name_)).is_err() || + CSPRNG(sc->ticket_key_hmac_, sizeof(sc->ticket_key_hmac_)).is_err() || + CSPRNG(sc->ticket_key_aes_, sizeof(sc->ticket_key_aes_)).is_err()) { return THROW_ERR_CRYPTO_OPERATION_FAILED( env, "Error generating ticket keys"); } @@ -1241,11 +1241,14 @@ int SecureContext::TicketCompatibilityCallback(SSL* ssl, if (enc) { memcpy(name, sc->ticket_key_name_, sizeof(sc->ticket_key_name_)); - if (RAND_bytes(iv, 16) <= 0 || - EVP_EncryptInit_ex(ectx, EVP_aes_128_cbc(), nullptr, - sc->ticket_key_aes_, iv) <= 0 || - HMAC_Init_ex(hctx, sc->ticket_key_hmac_, sizeof(sc->ticket_key_hmac_), - EVP_sha256(), nullptr) <= 0) { + if (CSPRNG(iv, 16).is_err() || + EVP_EncryptInit_ex( + ectx, EVP_aes_128_cbc(), nullptr, sc->ticket_key_aes_, iv) <= 0 || + HMAC_Init_ex(hctx, + sc->ticket_key_hmac_, + sizeof(sc->ticket_key_hmac_), + EVP_sha256(), + nullptr) <= 0) { return -1; } return 1; diff --git a/src/crypto/crypto_keygen.cc b/src/crypto/crypto_keygen.cc index af489967144d32..8def58a5f10cd9 100644 --- a/src/crypto/crypto_keygen.cc +++ b/src/crypto/crypto_keygen.cc @@ -81,7 +81,13 @@ KeyGenJobStatus SecretKeyGenTraits::DoKeyGen( SecretKeyGenConfig* params) { CHECK_LE(params->length, INT_MAX); params->out = MallocOpenSSL(params->length); - EntropySource(reinterpret_cast(params->out), params->length); + if (CSPRNG(reinterpret_cast(params->out), + params->length).is_err()) { + OPENSSL_clear_free(params->out, params->length); + params->out = nullptr; + params->length = 0; + return KeyGenJobStatus::FAILED; + } return KeyGenJobStatus::OK; } diff --git a/src/crypto/crypto_keygen.h b/src/crypto/crypto_keygen.h index ed7d5c0601fff1..1a933a247800d6 100644 --- a/src/crypto/crypto_keygen.h +++ b/src/crypto/crypto_keygen.h @@ -75,9 +75,6 @@ class KeyGenJob final : public CryptoJob { std::move(params)) {} void DoThreadPoolWork() override { - // Make sure the CSPRNG is properly seeded so the results are secure. - CheckEntropy(); - AdditionalParams* params = CryptoJob::params(); switch (KeyGenTraits::DoKeyGen(AsyncWrap::env(), params)) { diff --git a/src/crypto/crypto_random.cc b/src/crypto/crypto_random.cc index d0736a9cf1277a..2f9e9aacb1e652 100644 --- a/src/crypto/crypto_random.cc +++ b/src/crypto/crypto_random.cc @@ -66,8 +66,7 @@ bool RandomBytesTraits::DeriveBits( Environment* env, const RandomBytesConfig& params, ByteSource* unused) { - CheckEntropy(); // Ensure that OpenSSL's PRNG is properly seeded. - return RAND_bytes(params.buffer, params.size) != 0; + return CSPRNG(params.buffer, params.size).is_ok(); } void RandomPrimeConfig::MemoryInfo(MemoryTracker* tracker) const { @@ -156,12 +155,12 @@ Maybe RandomPrimeTraits::AdditionalConfig( return Just(true); } -bool RandomPrimeTraits::DeriveBits( - Environment* env, - const RandomPrimeConfig& params, - ByteSource* unused) { - - CheckEntropy(); +bool RandomPrimeTraits::DeriveBits(Environment* env, + const RandomPrimeConfig& params, + ByteSource* unused) { + // BN_generate_prime_ex() calls RAND_bytes_ex() internally. + // Make sure the CSPRNG is properly seeded. + CHECK(CSPRNG(nullptr, 0).is_ok()); if (BN_generate_prime_ex( params.prime.get(), diff --git a/src/crypto/crypto_util.cc b/src/crypto/crypto_util.cc index 805f8978b2ad1b..e878c5ea15d58f 100644 --- a/src/crypto/crypto_util.cc +++ b/src/crypto/crypto_util.cc @@ -60,26 +60,14 @@ int VerifyCallback(int preverify_ok, X509_STORE_CTX* ctx) { return 1; } -void CheckEntropy() { - for (;;) { - int status = RAND_status(); - CHECK_GE(status, 0); // Cannot fail. - if (status != 0) - break; - - // Give up, RAND_poll() not supported. - if (RAND_poll() == 0) - break; - } -} - -bool EntropySource(unsigned char* buffer, size_t length) { - // Ensure that OpenSSL's PRNG is properly seeded. - CheckEntropy(); - // RAND_bytes() can return 0 to indicate that the entropy data is not truly - // random. That's okay, it's still better than V8's stock source of entropy, - // which is /dev/urandom on UNIX platforms and the current time on Windows. - return RAND_bytes(buffer, length) != -1; +MUST_USE_RESULT CSPRNGResult CSPRNG(void* buffer, size_t length) { + do { + if (1 == RAND_status()) + if (1 == RAND_bytes(static_cast(buffer), length)) + return {true}; + } while (1 == RAND_poll()); + + return {false}; } int PasswordCallback(char* buf, int size, int rwflag, void* u) { diff --git a/src/crypto/crypto_util.h b/src/crypto/crypto_util.h index 4afae1884fe40e..dc3bb15cfb48a8 100644 --- a/src/crypto/crypto_util.h +++ b/src/crypto/crypto_util.h @@ -111,31 +111,18 @@ struct MarkPopErrorOnReturn { ~MarkPopErrorOnReturn() { ERR_pop_to_mark(); } }; -// Ensure that OpenSSL has enough entropy (at least 256 bits) for its PRNG. -// The entropy pool starts out empty and needs to fill up before the PRNG -// can be used securely. Once the pool is filled, it never dries up again; -// its contents is stirred and reused when necessary. -// -// OpenSSL normally fills the pool automatically but not when someone starts -// generating random numbers before the pool is full: in that case OpenSSL -// keeps lowering the entropy estimate to thwart attackers trying to guess -// the initial state of the PRNG. -// -// When that happens, we will have to wait until enough entropy is available. -// That should normally never take longer than a few milliseconds. -// -// OpenSSL draws from /dev/random and /dev/urandom. While /dev/random may -// block pending "true" randomness, /dev/urandom is a CSPRNG that doesn't -// block under normal circumstances. -// -// The only time when /dev/urandom may conceivably block is right after boot, -// when the whole system is still low on entropy. That's not something we can -// do anything about. -void CheckEntropy(); - -// Generate length bytes of random data. If this returns false, the data -// may not be truly random but it's still generally good enough. -bool EntropySource(unsigned char* buffer, size_t length); +struct CSPRNGResult { + const bool ok; + MUST_USE_RESULT bool is_ok() const { return ok; } + MUST_USE_RESULT bool is_err() const { return !ok; } +}; + +// Either succeeds with exactly |length| bytes of cryptographically +// strong pseudo-random data, or fails. This function may block. +// Don't assume anything about the contents of |buffer| on error. +// As a special case, |length == 0| can be used to check if the CSPRNG +// is properly seeded without consuming entropy. +MUST_USE_RESULT CSPRNGResult CSPRNG(void* buffer, size_t length); int PasswordCallback(char* buf, int size, int rwflag, void* u); diff --git a/src/inspector_io.cc b/src/inspector_io.cc index 7f52fc605933da..7e0b3ea63cff25 100644 --- a/src/inspector_io.cc +++ b/src/inspector_io.cc @@ -46,8 +46,7 @@ std::string ScriptPath(uv_loop_t* loop, const std::string& script_name) { // Used ver 4 - with numbers std::string GenerateID() { uint16_t buffer[8]; - CHECK(crypto::EntropySource(reinterpret_cast(buffer), - sizeof(buffer))); + CHECK(crypto::CSPRNG(buffer, sizeof(buffer)).is_ok()); char uuid[256]; snprintf(uuid, sizeof(uuid), "%04x%04x-%04x-%04x-%04x-%04x%04x%04x", diff --git a/src/node.cc b/src/node.cc index 71b3f7dcfe3cdd..75423472f0f301 100644 --- a/src/node.cc +++ b/src/node.cc @@ -1056,11 +1056,10 @@ InitializationResult InitializeOncePerProcess( // fipsinstall command. If the path to this file is incorrect no error // will be reported. // - // For Node.js this will mean that EntropySource will be called by V8 as - // part of its initialization process, and EntropySource will in turn call - // CheckEntropy. CheckEntropy will call RAND_status which will now always - // return 0, leading to an endless loop and the node process will appear to - // hang/freeze. + // For Node.js this will mean that CSPRNG() will be called by V8 as + // part of its initialization process, and CSPRNG() will in turn call + // call RAND_status which will now always return 0, leading to an endless + // loop and the node process will appear to hang/freeze. // Passing NULL as the config file will allow the default openssl.cnf file // to be loaded, but the default section in that file will not be used, @@ -1105,19 +1104,28 @@ InitializationResult InitializeOncePerProcess( OPENSSL_init(); } #endif - if (!crypto::ProcessFipsOptions()) { + if (!crypto::ProcessFipsOptions()) { result.exit_code = ERR_GET_REASON(ERR_peek_error()); result.early_return = true; fprintf(stderr, "OpenSSL error when trying to enable FIPS:\n"); ERR_print_errors_fp(stderr); return result; - } + } - // V8 on Windows doesn't have a good source of entropy. Seed it from - // OpenSSL's pool. - V8::SetEntropySource(crypto::EntropySource); + // Ensure CSPRNG is properly seeded. + CHECK(crypto::CSPRNG(nullptr, 0).is_ok()); + + V8::SetEntropySource([](unsigned char* buffer, size_t length) { + // V8 falls back to very weak entropy when this function fails + // and /dev/urandom isn't available. That wouldn't be so bad if + // the entropy was only used for Math.random() but it's also used for + // hash table and address space layout randomization. Better to abort. + CHECK(crypto::CSPRNG(buffer, length).is_ok()); + return true; + }); #endif // HAVE_OPENSSL && !defined(OPENSSL_IS_BORINGSSL) -} + } + per_process::v8_platform.Initialize( static_cast(per_process::cli_options->v8_thread_pool_size)); if (init_flags & kInitializeV8) {