Ok, I can see the error check could still be a bit shaky, a loop could possibly be used in clearLastError (documentation of the OpenSSL API is here: https://www.openssl.org/docs/manmaster/man3/ERR_get_error.html ). Not sure why clearLastError is called in unwrap however, maybe Mark can comment on that one. The TODO is accurate: ideally every SSL call should check the error.

BTW, I doubt this reproduces anything, ab works just fine, so curl isn't going to be doing anything special beyond that.

The NPE in SecureNioChannel.close is possible, it would be a cosmetic error but the code could be more defensive.

I cannot reproduce the issue, please test with the most recent 9.0 release.

Since this better matches the OpenSSL documentation, I am ok conceptually to modify clearLastError to do:
while (SSL.getLastErrorNumber() != SSL.SSL_ERROR_NONE);

I have reproduced the problem with tomcat version 9.0.43:


Feb 11, 2021 11:49:43 AM org.apache.catalina.core.AprLifecycleListener lifecycleEvent
INFO: Loaded Apache Tomcat Native library [1.2.26] using APR version [1.4.8].
Feb 11, 2021 11:49:43 AM org.apache.catalina.core.AprLifecycleListener lifecycleEvent
INFO: APR capabilities: IPv6 [true], sendfile [true], accept filters [false], random [true].
Feb 11, 2021 11:49:43 AM org.apache.catalina.core.AprLifecycleListener lifecycleEvent
INFO: APR/OpenSSL configuration: useAprConnector [false], useOpenSSL [true]
Feb 11, 2021 11:49:43 AM org.apache.catalina.core.AprLifecycleListener initializeSSL
INFO: OpenSSL successfully initialized [OpenSSL 1.0.2u  20 Dec 2019]

....


Feb 11, 2021 12:05:01 PM org.apache.tomcat.util.net.openssl.OpenSSLEngine checkLastError
FINE: OpenSSL error: [336462231] message: [error:140E0197:SSL routines:SSL_shutdown:shutdown while in init]
Feb 11, 2021 12:05:01 PM org.apache.coyote.http11.Http11Processor service
FINE: Error parsing HTTP request header
javax.net.ssl.SSLException: error:140E0197:SSL routines:SSL_shutdown:shutdown while in init
        at org.apache.tomcat.util.net.openssl.OpenSSLEngine.checkLastError(OpenSSLEngine.java:951)
        at org.apache.tomcat.util.net.openssl.OpenSSLEngine.pendingReadableBytesInSSL(OpenSSLEngine.java:636)
        at org.apache.tomcat.util.net.openssl.OpenSSLEngine.unwrap(OpenSSLEngine.java:558)
        at javax.net.ssl.SSLEngine.unwrap(SSLEngine.java:629)
        at org.apache.tomcat.util.net.SecureNioChannel.read(SecureNioChannel.java:637)
        at org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper.fillReadBuffer(NioEndpoint.java:1320)
        at org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper.read(NioEndpoint.java:1232)
        at org.apache.coyote.http11.Http11InputBuffer.fill(Http11InputBuffer.java:791)
        at org.apache.coyote.http11.Http11InputBuffer.parseRequestLine(Http11InputBuffer.java:359)
        at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:261)
        at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
        at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:887)
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1684)
        at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
        at com.broadsoft.xsp.platform.InstrumentedExecutor$Tracker.run(InstrumentedExecutor.java:413)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

I can't recreate this using the provided test case, Tomcat Native 1.2.26 and the latest OpenSSL 1.1.1 source code.

I'll note that Tomcat 1.2.26 won't compile with OpenSSL 1.0.2 so I do wonder exactly what versions were in used in the tests described here.

I'll also note that OpenSSL 1.0.2 is no longer supported.

Please retest with the latest OpenSSL 1.1.1 release.

(In reply to Mark Thomas from comment #4)
> I can't recreate this using the provided test case, Tomcat Native 1.2.26 and
> the latest OpenSSL 1.1.1 source code.
> 
> I'll note that Tomcat 1.2.26 won't compile with OpenSSL 1.0.2 so I do wonder
> exactly what versions were in used in the tests described here.
> 
> I'll also note that OpenSSL 1.0.2 is no longer supported.
> 
> Please retest with the latest OpenSSL 1.1.1 release.

Should I still replace clearLastError with this ?

    private static void clearLastError() {
        while (SSL.getLastErrorNumber() != SSL.SSL_ERROR_NONE);
    }

This does not seem unreasonable given the docs ...

Yes, the OP is correct that the clearLastError call in unwrap is there is part of this fix:
https://github.com/apache/tomcat/commit/ebab25

I agree that using a loop looks to be the right approach here.

Ok, so clearLastError will now align with the OpenSSL documentation using the loop. The change will be in 10.0.3, 9.0.44 and 8.5.64 [along with the NPE fix]. We could not reproduce, so you will have to verify this is fixed.

Thanks, Remy. I'll update this bug report when I get the chance to test the latest tomcat version.