crypto: fix crash when calling digest after piping

When piping data into an SHA3 hash, EVP_DigestFinal_ex is called in hash._flush, bypassing safeguards in the JavaScript layer. Calling hash.digest causes EVP_DigestFinal_ex to be called again, resulting in a segmentation fault in the SHA3 implementation of OpenSSL. A relatively easy solution is to cache the result of calling EVP_DigestFinal_ex until the Hash object is garbage collected.
tniessen · Jun 16, 2019 · Jun 17, 2019 · Jun 16, 2019 · b6d2d7923e11292722bb504c89e736d35e068494
commit b6d2d7923e11292722bb504c89e736d35e068494
diff --git a/src/node_crypto.cc b/src/node_crypto.cc
@@ -4634,16 +4634,20 @@ void Hash::HashDigest(const FunctionCallbackInfo<Value>& args) {
     encoding = ParseEncoding(env->isolate(), args[0], BUFFER);
   }
 
-  unsigned char md_value[EVP_MAX_MD_SIZE];
-  unsigned int md_len;
-
-  EVP_DigestFinal_ex(hash->mdctx_.get(), md_value, &md_len);
+  if (hash->md_len_ == 0) {
+    // Some hash algorithms such as SHA3 do not support calling
+    // EVP_DigestFinal_ex more than once, however, Hash._flush
+    // and Hash.digest can both be used to retrieve the digest,
+    // so we need to cache it.
+    // See https://github.com/nodejs/node/issues/28245.
+    EVP_DigestFinal_ex(hash->mdctx_.get(), hash->md_value_, &hash->md_len_);
+  }
 
   Local<Value> error;
   MaybeLocal<Value> rc =
       StringBytes::Encode(env->isolate(),
-                          reinterpret_cast<const char*>(md_value),
-                          md_len,
+                          reinterpret_cast<const char*>(hash->md_value_),
+                          hash->md_len_,
                           encoding,
                           &error);
   if (rc.IsEmpty()) {

diff --git a/src/node_crypto.h b/src/node_crypto.h
@@ -595,12 +595,15 @@ class Hash : public BaseObject {
 
   Hash(Environment* env, v8::Local<v8::Object> wrap)
       : BaseObject(env, wrap),
-        mdctx_(nullptr) {
+        mdctx_(nullptr),
+        md_len_(0) {
     MakeWeak();
   }
 
  private:
   EVPMDPointer mdctx_;
+  unsigned char md_value_[EVP_MAX_MD_SIZE];
+  unsigned int md_len_;
 };
 
 class SignBase : public BaseObject {

diff --git a/test/parallel/test-crypto-hash-stream-pipe.js b/test/parallel/test-crypto-hash-stream-pipe.js
@@ -30,11 +30,17 @@ const crypto = require('crypto');
 
 const stream = require('stream');
 const s = new stream.PassThrough();
-const h = crypto.createHash('sha1');
-const expect = '15987e60950cf22655b9323bc1e281f9c4aff47e';
+const h = crypto.createHash('sha3-512');
+const expect = '36a38a2a35e698974d4e5791a3f05b05' +
+               '198235381e864f91a0e8cd6a26b677ec' +
+               'dcde8e2b069bd7355fabd68abd6fc801' +
+               '19659f25e92f8efc961ee3a7c815c758';
 
 s.pipe(h).on('data', common.mustCall(function(c) {
   assert.strictEqual(c, expect);
+  // Calling digest() after piping into a stream with SHA3 should not cause
+  // a segmentation fault, see https://github.com/nodejs/node/issues/28245.
+  assert.strictEqual(h.digest('hex'), expect);
 })).setEncoding('hex');
 
 s.end('aoeu');