mina-sshd

mina-sshd copied to clipboard

…yPair() method call.

The keyPairGenerator object is a bouncycastle implementation of the java.security.KeyPairGenerator class. The generateKeyPair method in class org.bouncycastle.jcajce.provider.asymmetric.edec.KeyPairGeneratorSpi is not thread safe, so calling the generateKeyPair method must be synchronized, otherwise calling this method by multiple threads will often cause a NullPointerException due to a race conditions.

Consider the following scenario: two threads simultaneously reach the generateKeyPair() method in class org.bouncycastle.jcajce.provider.asymmetric.edec.KeyPairGeneratorSpi. Thread one performs the if (!initialised) check. The "initialised" variable is false. Therefore, the setupGenerator(algorithm) method is executed. In the setupGenerator method, the "initialised" variable is assigned true at the very beginning. And at this moment, execution of the thread one is suspended and execution of the thread two continues. Thread two evaluates the "initialised" variable. The variable is true therefore thread two executes the further command AsymmetricCipherKeyPair kp = generator.generateKeyPair(); the generator is not yet correctly initialized. Thread two continues its execution and eventually throws a NullPointerException, which is the result of the generator not being initialized correctly because the setupGenerator method was not executed to completion even though the initialised variable was already set to true. The callstack looks like this: Caused by: java.lang.NullPointerException at org.bouncycastle.math.ec.rfc7748.X25519.generatePrivateKey(X25519.java:54) at org.bouncycastle.crypto.params.X25519PrivateKeyParameters.(X25519PrivateKeyParameters.java:24) at org.bouncycastle.crypto.generators.X25519KeyPairGenerator.generateKeyPair(X25519KeyPairGenerator.java:23) at org.bouncycastle.jcajce.provider.asymmetric.edec.KeyPairGeneratorSpi.generateKeyPair(KeyPairGeneratorSpi.java:193) at java.base/java.security.KeyPairGenerator$Delegate.generateKeyPair(KeyPairGenerator.java:722) at org.apache.sshd.common.kex.MontgomeryCurve.generateKeyPair(MontgomeryCurve.java:156) The org.bouncycastle.math.ec.rfc7748.X25519.generatePrivateKey(SecureRandom random, byte[] k) method executes the random.nextBytes(k) instruction. In this case, the "random" argument is null, since the setupGenerator(algorithm) method was not completed yet. The result is a NullPointerException.

This change is the result of an investigation into the cause of the flaky tests in Gerrit.

This commit message is more an issue description. Please open a bug issue and explain all that there.

Then the commit message can focus on the change here (synchronizing access to a shared KeyPairGenerator, which may not be thread-safe).

Is MontgomeryCurve the only place where this problematic usage pattern occurs? Could the same problem also exist for the KeyFactory?

Created new issue: 470. Updated commit message. While investigating the issue I didn't notice thread-safety problems with KeyFactory.

Edited issue description: https://github.com/apache/mina-sshd/issues/470

Thank you.