[
https://issues.apache.org/jira/browse/SSHD-966?focusedWorklogId=761050&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-761050
]
ASF GitHub Bot logged work on SSHD-966:
---------------------------------------
Author: ASF GitHub Bot
Created on: 22/Apr/22 19:35
Start Date: 22/Apr/22 19:35
Worklog Time Spent: 10m
Work Description: tomaswolf commented on code in PR #217:
URL: https://github.com/apache/mina-sshd/pull/217#discussion_r856517459
##########
docs/kex.md:
##########
@@ -0,0 +1,131 @@
+## SSH Key Exchange
+
+**Key Exchange** (or **KEX** for short) is a sub-protocol in the SSH protocol
+enabling the two parties in a connection to exchange information and compute a
+shared secret that will then be used for encrypting all following messages.
+
+A key exchange runs initially, after the network connection is established,
+but before authentication. Later on, KEX may be repeated; when exactly,
+depends on various settings:
+
+* it is re-run when a certain amount of bytes have been sent since the last
KEX.
+* it may be re-run when a certain number of SSH packets have been sent since
the last KEX.
+* it may be re-run when a certain time has elapsed since the last KEX.
+
+The purpose of re-running KEX is to establish a new shared secret from time to
+time, changing the encryption for all subsequent messages, until the next KEX.
+This mitigates possible attacks against the encryption when a lot of data is
sent
+using the same encryption with the same shared secret.
+
+KEX is specified in [RFC 4253, section
7](https://tools.ietf.org/html/rfc4253#section-7).
+
+### Basic KEX message exchange
+
+A key exchange starts with both parties sending a SSH_MSG_KEX_INIT message,
+passing along information about available cryptographic algorithms. Both
+parties can decide from this information what kind of key exchange to perform.
+They then run the cryptographic key exchange protocol, which may incur several
+message exchanges. Once that protocol ends, both sides know the shared secret.
+At that point they both send a SSH_MSG_NEW_KEYS message to tell the other side
+they're ready, and use the new encryption for any subsequent outgoing message.
+The SSH_MSG_NEW_KEYS message itself is still sent with the old encryption. On
+receiving a SSH_MSG_NEW_KEYS message, each side starts using the new encryption
+to decrypt any subsequent incoming messages. Note that the SSH_MSG_NEW_KEYS
+message does not contain the new encryption key or the shared secret; it is
+just a marker message telling the other side that from now on, the new
encryption
+will be used.
+
+Apache MINA sshd maintains internally in
[`AbstractSession`](../sshd-core/src/main/java/org/apache/sshd/common/session/helpers/AbstractSession.java)
+a *KEX state* (in Java
[`KexState`](../sshd-common/src/main/java/org/apache/sshd/common/kex/KexState.java)).
+This models the key exchange on one side of the connection as a state machine
+going through the states `DONE`, `INIT`, `RUN`, `KEYS`, `DONE`.
+
+
+
+These states mark important points in the key exchange sub-protocol:
+
+* `DONE` means no key exchange is ongoing, this side has received the peer's
SSH_MSG_NEW_KEYS message, and both sides have a shared secret that they use for
encryption.
+* `INIT` means this side of the connection has requested a new KEX; it has
sent it's SSH_MSG_KEX_INIT message.
+* `RUN` means this side has received the peer's SSH_MSG_KEX_INIT message, and
key exchange is running now to determine a new shared secret.
+* `KEYS` means the key exchange has been done; both sides know the shared
secret, and this side has sent its SSH_MS_NEW_KEYS message.
+* When the peer's SSH_MSG_NEW_KEYS message is received, the state changes back
to `DONE`.
+
+In Apache MINA sshd, there are methods in `AbstractSession` for each of the KEX
+messages:
+
+* `requestNewKeyExchange`: switches from `DONE` to `INIT` and calls
`sendKexInit` to send the SSH_MSG_KEX_INIT message.
+* `handleKexInit`: receives the peer's SSH_MSG_KEX_INIT message; switches to
`RUN`.
+* `sendNewKeys`: switches from `RUN` to `KEYS` and sends this side's
SSH_MS_NEW_KEYS message.
+* `handleNewKeys`: receives the peer's SSH_MSG_KEX_INIT message; switches from
`KEYS` to `DONE`.
+
+
Review Comment:
I can also use SVG. Won't make it much easier to change the diagrams,
though. Inkscape has some problems with the SVG exported by the tool I used.
Binary files in git are totally fine. What is problematic are large files.
But I agree, let's use SVG for diagrams, and I'll also put the original
source somewhere.
Issue Time Tracking
-------------------
Worklog Id: (was: 761050)
Time Spent: 3h (was: 2h 50m)
> Deadlock on disconnection at the end of key-exchange
> ----------------------------------------------------
>
> Key: SSHD-966
> URL: https://issues.apache.org/jira/browse/SSHD-966
> Project: MINA SSHD
> Issue Type: Bug
> Affects Versions: 2.0.0
> Reporter: Francois Ferrand
> Assignee: Lyor Goldstein
> Priority: Major
> Time Spent: 3h
> Remaining Estimate: 0h
>
> We are using git-repo to download projects from Gerrit server, using SSH.
> Gerrit is in version 2.16.16. which uses SSHD 2.0.0 and Mina 2.0.17 with NIO2
> backend.
> One particularity of this setup is that git-repo creates a single control
> master channel, and then downloads *lots* of Git repositories (500
> repositories, some of them relatively large), with some degree of
> parallelism. This takes a long time, lots of data, and the multiplexed
> connections are handled by gerrit in multiple threads.
> In some cases, we experience a deadlock when an error happens at the end of
> the key exchange, while sending pending packets:
> {noformat}
> Warning, the following threads are deadlocked : SSH git-upload-pack /project1
> (myuser), sshd-SshServer[df5f657]-nio2-thread-3
> "SSH git-upload-pack /project1 (myuser)" prio=1 BLOCKED
>
> org.apache.sshd.common.session.helpers.AbstractSession.writePacket(AbstractSession.java:1107)
>
> org.apache.sshd.common.channel.AbstractChannel.writePacket(AbstractChannel.java:798)
>
> org.apache.sshd.common.channel.ChannelOutputStream.flush(ChannelOutputStream.java:227)
>
> org.apache.sshd.common.channel.ChannelOutputStream.write(ChannelOutputStream.java:127)
>
> org.eclipse.jgit.transport.UploadPack$ResponseBufferedOutputStream.write(UploadPack.java:2183)
>
> org.eclipse.jgit.transport.SideBandOutputStream.writeBuffer(SideBandOutputStream.java:174)
>
> org.eclipse.jgit.transport.SideBandOutputStream.write(SideBandOutputStream.java:153)
>
> org.eclipse.jgit.internal.storage.pack.PackOutputStream.write(PackOutputStream.java:132)
>
> org.eclipse.jgit.internal.storage.file.PackFile.copyAsIs2(PackFile.java:614)
>
> org.eclipse.jgit.internal.storage.file.PackFile.copyAsIs(PackFile.java:433)
>
> org.eclipse.jgit.internal.storage.file.WindowCursor.copyObjectAsIs(WindowCursor.java:221)
>
> org.eclipse.jgit.internal.storage.pack.PackWriter.writeObjectImpl(PackWriter.java:1644)
>
> org.eclipse.jgit.internal.storage.pack.PackWriter.writeObject(PackWriter.java:1621)
>
> org.eclipse.jgit.internal.storage.pack.PackOutputStream.writeObject(PackOutputStream.java:171)
>
> org.eclipse.jgit.internal.storage.file.WindowCursor.writeObjects(WindowCursor.java:229)
>
> org.eclipse.jgit.internal.storage.pack.PackWriter.writeObjects(PackWriter.java:1609)
>
> org.eclipse.jgit.internal.storage.pack.PackWriter.writeObjects(PackWriter.java:1597)
>
> org.eclipse.jgit.internal.storage.pack.PackWriter.writePack(PackWriter.java:1154)
> org.eclipse.jgit.transport.UploadPack.sendPack(UploadPack.java:2133)
> org.eclipse.jgit.transport.UploadPack.sendPack(UploadPack.java:1947)
> org.eclipse.jgit.transport.UploadPack.service(UploadPack.java:971)
> org.eclipse.jgit.transport.UploadPack.upload(UploadPack.java:776)
> com.google.gerrit.sshd.commands.Upload.runImpl(Upload.java:77)
>
> com.google.gerrit.sshd.AbstractGitCommand.service(AbstractGitCommand.java:98)
>
> com.google.gerrit.sshd.AbstractGitCommand.access$000(AbstractGitCommand.java:31)
>
> com.google.gerrit.sshd.AbstractGitCommand$1.run(AbstractGitCommand.java:63)
> com.google.gerrit.sshd.BaseCommand$TaskThunk.run(BaseCommand.java:467)
>
> com.google.gerrit.server.logging.LoggingContextAwareRunnable.run(LoggingContextAwareRunnable.java:83)
> java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
> java.util.concurrent.FutureTask.run(FutureTask.java:266)
>
> java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
>
> java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
> com.google.gerrit.server.git.WorkQueue$Task.run(WorkQueue.java:646)
>
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
>
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
> java.lang.Thread.run(Thread.java:748)
> "sshd-SshServer[df5f657]-nio2-thread-3" daemon prio=5 BLOCKED
>
> org.apache.sshd.common.channel.ChannelOutputStream.close(ChannelOutputStream.java:249)
> org.apache.sshd.common.util.io.IoUtils.closeQuietly(IoUtils.java:151)
>
> org.apache.sshd.server.channel.ChannelSession.doCloseImmediately(ChannelSession.java:205)
>
> org.apache.sshd.common.util.closeable.AbstractCloseable.close(AbstractCloseable.java:83)
>
> org.apache.sshd.common.channel.AbstractChannel.close(AbstractChannel.java:576)
>
> org.apache.sshd.common.util.closeable.ParallelCloseable.doClose(ParallelCloseable.java:65)
>
> org.apache.sshd.common.util.closeable.SimpleCloseable.close(SimpleCloseable.java:63)
>
> org.apache.sshd.common.util.closeable.AbstractInnerCloseable.doCloseImmediately(AbstractInnerCloseable.java:46)
>
> org.apache.sshd.common.util.closeable.AbstractCloseable.close(AbstractCloseable.java:83)
>
> org.apache.sshd.common.util.closeable.ParallelCloseable.doClose(ParallelCloseable.java:65)
>
> org.apache.sshd.common.util.closeable.SimpleCloseable.close(SimpleCloseable.java:63)
>
> org.apache.sshd.common.util.closeable.SequentialCloseable$1.operationComplete(SequentialCloseable.java:56)
>
> org.apache.sshd.common.util.closeable.SequentialCloseable$1.operationComplete(SequentialCloseable.java:45)
>
> org.apache.sshd.common.util.closeable.SequentialCloseable.doClose(SequentialCloseable.java:69)
>
> org.apache.sshd.common.util.closeable.SimpleCloseable.close(SimpleCloseable.java:63)
>
> org.apache.sshd.common.util.closeable.AbstractInnerCloseable.doCloseImmediately(AbstractInnerCloseable.java:46)
>
> org.apache.sshd.common.util.closeable.AbstractCloseable.close(AbstractCloseable.java:83)
>
> org.apache.sshd.common.session.helpers.AbstractSession.exceptionCaught(AbstractSession.java:973)
>
> org.apache.sshd.common.session.helpers.AbstractSessionIoHandler.exceptionCaught(AbstractSessionIoHandler.java:53)
>
> org.apache.sshd.common.io.nio2.Nio2Session.exceptionCaught(Nio2Session.java:186)
>
> org.apache.sshd.common.io.nio2.Nio2Session.handleWriteCycleFailure(Nio2Session.java:460)
>
> org.apache.sshd.common.io.nio2.Nio2Session$2.onFailed(Nio2Session.java:415)
>
> org.apache.sshd.common.io.nio2.Nio2CompletionHandler.lambda$failed$1(Nio2CompletionHandler.java:46)
>
> org.apache.sshd.common.io.nio2.Nio2CompletionHandler$$Lambda$627/1874891543.run(Unknown
> Source)
> java.security.AccessController.doPrivileged(Native Method)
>
> org.apache.sshd.common.io.nio2.Nio2CompletionHandler.failed(Nio2CompletionHandler.java:45)
> sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:128)
> sun.nio.ch.Invoker.invokeDirect(Invoker.java:157)
>
> sun.nio.ch.UnixAsynchronousSocketChannelImpl.implWrite(UnixAsynchronousSocketChannelImpl.java:736)
>
> sun.nio.ch.AsynchronousSocketChannelImpl.write(AsynchronousSocketChannelImpl.java:382)
>
> sun.nio.ch.AsynchronousSocketChannelImpl.write(AsynchronousSocketChannelImpl.java:399)
>
> org.apache.sshd.common.io.nio2.Nio2Session.doWriteCycle(Nio2Session.java:401)
>
> org.apache.sshd.common.io.nio2.Nio2Session.startWriting(Nio2Session.java:386)
>
> org.apache.sshd.common.io.nio2.Nio2Session.writePacket(Nio2Session.java:169)
>
> org.apache.sshd.common.session.helpers.AbstractSession.doWritePacket(AbstractSession.java:1181)
>
> org.apache.sshd.common.session.helpers.AbstractSession.sendPendingPackets(AbstractSession.java:910)
>
> org.apache.sshd.common.session.helpers.AbstractSession.handleNewKeys(AbstractSession.java:875)
>
> org.apache.sshd.common.session.helpers.AbstractSession.doHandleMessage(AbstractSession.java:606)
>
> org.apache.sshd.common.session.helpers.AbstractSession.handleMessage(AbstractSession.java:555)
>
> org.apache.sshd.common.session.helpers.AbstractSession.decode(AbstractSession.java:1527)
>
> org.apache.sshd.common.session.helpers.AbstractSession.messageReceived(AbstractSession.java:516)
>
> org.apache.sshd.common.session.helpers.AbstractSessionIoHandler.messageReceived(AbstractSessionIoHandler.java:63)
>
> org.apache.sshd.common.io.nio2.Nio2Session.handleReadCycleCompletion(Nio2Session.java:339)
>
> org.apache.sshd.common.io.nio2.Nio2Session$1.onCompleted(Nio2Session.java:318)
>
> org.apache.sshd.common.io.nio2.Nio2Session$1.onCompleted(Nio2Session.java:315)
>
> org.apache.sshd.common.io.nio2.Nio2CompletionHandler.lambda$completed$0(Nio2CompletionHandler.java:38)
>
> org.apache.sshd.common.io.nio2.Nio2CompletionHandler$$Lambda$349/1690110070.run(Unknown
> Source)
> java.security.AccessController.doPrivileged(Native Method)
>
> org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:37)
> sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:126)
> sun.nio.ch.Invoker$2.run(Invoker.java:218)
>
> sun.nio.ch.AsynchronousChannelGroupImpl$1.run(AsynchronousChannelGroupImpl.java:112)
>
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
>
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
> java.lang.Thread.run(Thread.java:748)
> "SSH git-upload-pack /project2 (myuser)" prio=1 BLOCKED
>
> org.apache.sshd.common.session.helpers.AbstractSession.writePacket(AbstractSession.java:1107)
>
> org.apache.sshd.common.channel.AbstractChannel.writePacket(AbstractChannel.java:798)
>
> org.apache.sshd.common.channel.ChannelOutputStream.flush(ChannelOutputStream.java:227)
>
> org.apache.sshd.common.channel.ChannelOutputStream.write(ChannelOutputStream.java:127)
>
> org.eclipse.jgit.transport.UploadPack$ResponseBufferedOutputStream.write(UploadPack.java:2183)
>
> org.eclipse.jgit.transport.SideBandOutputStream.writeBuffer(SideBandOutputStream.java:174)
>
> org.eclipse.jgit.transport.SideBandOutputStream.write(SideBandOutputStream.java:153)
>
> org.eclipse.jgit.internal.storage.pack.PackOutputStream.write(PackOutputStream.java:132)
>
> org.eclipse.jgit.internal.storage.file.PackFile.copyAsIs2(PackFile.java:614)
>
> org.eclipse.jgit.internal.storage.file.PackFile.copyAsIs(PackFile.java:433)
>
> org.eclipse.jgit.internal.storage.file.WindowCursor.copyObjectAsIs(WindowCursor.java:221)
>
> org.eclipse.jgit.internal.storage.pack.PackWriter.writeObjectImpl(PackWriter.java:1644)
>
> org.eclipse.jgit.internal.storage.pack.PackWriter.writeObject(PackWriter.java:1621)
>
> org.eclipse.jgit.internal.storage.pack.PackOutputStream.writeObject(PackOutputStream.java:171)
>
> org.eclipse.jgit.internal.storage.file.WindowCursor.writeObjects(WindowCursor.java:229)
>
> org.eclipse.jgit.internal.storage.pack.PackWriter.writeObjects(PackWriter.java:1609)
>
> org.eclipse.jgit.internal.storage.pack.PackWriter.writeObjects(PackWriter.java:1597)
>
> org.eclipse.jgit.internal.storage.pack.PackWriter.writePack(PackWriter.java:1154)
> org.eclipse.jgit.transport.UploadPack.sendPack(UploadPack.java:2133)
> org.eclipse.jgit.transport.UploadPack.sendPack(UploadPack.java:1947)
> org.eclipse.jgit.transport.UploadPack.service(UploadPack.java:971)
> org.eclipse.jgit.transport.UploadPack.upload(UploadPack.java:776)
> com.google.gerrit.sshd.commands.Upload.runImpl(Upload.java:77)
>
> com.google.gerrit.sshd.AbstractGitCommand.service(AbstractGitCommand.java:98)
>
> com.google.gerrit.sshd.AbstractGitCommand.access$000(AbstractGitCommand.java:31)
>
> com.google.gerrit.sshd.AbstractGitCommand$1.run(AbstractGitCommand.java:63)
> com.google.gerrit.sshd.BaseCommand$TaskThunk.run(BaseCommand.java:467)
>
> com.google.gerrit.server.logging.LoggingContextAwareRunnable.run(LoggingContextAwareRunnable.java:83)
> java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
> java.util.concurrent.FutureTask.run(FutureTask.java:266)
>
> java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
>
> java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
> com.google.gerrit.server.git.WorkQueue$Task.run(WorkQueue.java:646)
>
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
>
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
> java.lang.Thread.run(Thread.java:748)
> {noformat}
> In AbstractSession.handleNewKeys(), there is a lock on {{pendingEvents}},
> while trying to send these packets; when sending the packets fails, an
> exception is generated, which causes the channel to get closed by calling
> ChannelOutputStream.close(), which is a synchronized method.
> At the same time, some other threads are trying to write data to the session:
> it calls ChannelOutputStream.write(), which is also a synchronized method,
> which calls AbstractSession.writePacket() which attempts to lock
> {{pendingPackets}} to queue the packets.
> *NOTE*: in our setup, we can reproduce this quite easily by increasing the
> parallelism in git-repo, reducing the values of waitTimeout
> (WAIT_FOR_SPACE_TIMEOUT), rekeyBytesLimit (REKEY_TIME_LIMIT) and
> rekeyTimeLimit (REKEY_TIME_LIMIT) configuration options.
--
This message was sent by Atlassian Jira
(v8.20.7#820007)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
