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Don't dispose channel when completing SshCommand (#1596)

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The new(-ish) implementation of SshCommand has a race condition for short-lived
commands where SSH_MSG_CHANNEL_CLOSE may be processed on the message loop thread
before SSH_MSG_CHANNEL_SUCCESS is waited upon on the Execute (main) thread. This
manifests in an ArgumentNull/NullReference exception on the wait handle because
the channel has already been closed and disposed.

Fix this by only delaying the channel dispose until the command dispose.
This commit is contained in:
Rob Hague
2025-02-19 12:16:12 +00:00
committed by GitHub
parent a0c6bac3a7
commit 99ef23cd87
4 changed files with 22 additions and 99 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/Renci.SshNet/SshCommand.cs
+21 -20
View File
@@ -21,7 +21,7 @@ namespace Renci.SshNet
private readonly ISession _session;
private readonly Encoding _encoding;
private IChannelSession? _channel;
private IChannelSession _channel;
private TaskCompletionSource<object>? _tcs;
private CancellationTokenSource? _cts;
private CancellationTokenRegistration _tokenRegistration;
@@ -142,14 +142,14 @@ namespace Renci.SshNet
/// </example>
public Stream CreateInputStream()
{
if (_channel == null)
if (!_channel.IsOpen)
{
throw new InvalidOperationException($"The input stream can be used only after calling BeginExecute and before calling EndExecute.");
throw new InvalidOperationException("The input stream can be used only during execution.");
}
if (_inputStream != null)
{
throw new InvalidOperationException($"The input stream already exists.");
throw new InvalidOperationException("The input stream already exists.");
}
_inputStream = new ChannelInputStream(_channel);
@@ -226,6 +226,7 @@ namespace Renci.SshNet
ExtendedOutputStream = new PipeStream();
_session.Disconnected += Session_Disconnected;
_session.ErrorOccured += Session_ErrorOccured;
_channel = _session.CreateChannelSession();
}
/// <summary>
@@ -257,6 +258,8 @@ namespace Renci.SshNet
throw new InvalidOperationException("Asynchronous operation is already in progress.");
}
UnsubscribeFromChannelEvents(dispose: true);
OutputStream.Dispose();
ExtendedOutputStream.Dispose();
@@ -265,6 +268,7 @@ namespace Renci.SshNet
// so we just need to reinitialise them for subsequent executions.
OutputStream = new PipeStream();
ExtendedOutputStream = new PipeStream();
_channel = _session.CreateChannelSession();
}
_exitStatus = default;
@@ -282,7 +286,6 @@ namespace Renci.SshNet
_tcs = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
_userToken = cancellationToken;
_channel = _session.CreateChannelSession();
_channel.DataReceived += Channel_DataReceived;
_channel.ExtendedDataReceived += Channel_ExtendedDataReceived;
_channel.RequestReceived += Channel_RequestReceived;
@@ -542,7 +545,10 @@ namespace Renci.SshNet
}
}
UnsubscribeFromEventsAndDisposeChannel();
// We don't dispose the channel here to avoid a race condition
// where SSH_MSG_CHANNEL_CLOSE arrives before _channel starts
// waiting for a response in _channel.SendExecRequest().
UnsubscribeFromChannelEvents(dispose: false);
OutputStream.Dispose();
ExtendedOutputStream.Dispose();
@@ -568,7 +574,7 @@ namespace Renci.SshNet
Debug.Assert(!exitSignalInfo.WantReply, "exit-signal is want_reply := false by definition.");
}
else if (e.Info.WantReply && _channel?.RemoteChannelNumber is uint remoteChannelNumber)
else if (e.Info.WantReply && sender is IChannel { RemoteChannelNumber: uint remoteChannelNumber })
{
var replyMessage = new ChannelFailureMessage(remoteChannelNumber);
_session.SendMessage(replyMessage);
@@ -591,20 +597,13 @@ namespace Renci.SshNet
}
/// <summary>
/// Unsubscribes the current <see cref="SshCommand"/> from channel events, and disposes
/// the <see cref="_channel"/>.
/// Unsubscribes the current <see cref="SshCommand"/> from channel events, and optionally,
/// disposes <see cref="_channel"/>.
/// </summary>
private void UnsubscribeFromEventsAndDisposeChannel()
private void UnsubscribeFromChannelEvents(bool dispose)
{
var channel = _channel;
if (channel is null)
{
return;
}
_channel = null;
// unsubscribe from events as we do not want to be signaled should these get fired
// during the dispose of the channel
channel.DataReceived -= Channel_DataReceived;
@@ -612,8 +611,10 @@ namespace Renci.SshNet
channel.RequestReceived -= Channel_RequestReceived;
channel.Closed -= Channel_Closed;
// actually dispose the channel
channel.Dispose();
if (dispose)
{
channel.Dispose();
}
}
/// <summary>
@@ -645,7 +646,7 @@ namespace Renci.SshNet
// unsubscribe from channel events to ensure other objects that we're going to dispose
// are not accessed while disposing
UnsubscribeFromEventsAndDisposeChannel();
UnsubscribeFromChannelEvents(dispose: true);
_inputStream?.Dispose();
_inputStream = null;
test/Renci.SshNet.Tests/Classes/SshCommandTest_EndExecute.cs
-72
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@@ -1,72 +0,0 @@
using System;
using System.Globalization;
using System.Text;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using Moq;
using Renci.SshNet.Channels;
using Renci.SshNet.Common;
using Renci.SshNet.Tests.Common;
namespace Renci.SshNet.Tests.Classes
{
[TestClass]
public class SshCommand_EndExecute : TestBase
{
private Mock<ISession> _sessionMock;
private Mock<IChannelSession> _channelSessionMock;
private string _commandText;
private Encoding _encoding;
private SshCommand _sshCommand;
protected override void OnInit()
{
base.OnInit();
_sessionMock = new Mock<ISession>(MockBehavior.Strict);
_commandText = new Random().Next().ToString(CultureInfo.InvariantCulture);
_encoding = Encoding.UTF8;
_channelSessionMock = new Mock<IChannelSession>(MockBehavior.Strict);
_sshCommand = new SshCommand(_sessionMock.Object, _commandText, _encoding);
}
[TestMethod]
public void EndExecute_ChannelClosed_ShouldDisposeChannelSession()
{
var seq = new MockSequence();
_sessionMock.InSequence(seq).Setup(p => p.CreateChannelSession()).Returns(_channelSessionMock.Object);
_channelSessionMock.InSequence(seq).Setup(p => p.Open());
_channelSessionMock.InSequence(seq).Setup(p => p.SendExecRequest(_commandText))
.Returns(true)
.Raises(c => c.Closed += null, new ChannelEventArgs(5));
_channelSessionMock.InSequence(seq).Setup(p => p.Dispose());
var asyncResult = _sshCommand.BeginExecute();
_sshCommand.EndExecute(asyncResult);
_channelSessionMock.Verify(p => p.Dispose(), Times.Once);
}
[TestMethod]
public void EndExecute_ChannelOpen_ShouldSendEofAndCloseAndDisposeChannelSession()
{
var seq = new MockSequence();
_sessionMock.InSequence(seq).Setup(p => p.CreateChannelSession()).Returns(_channelSessionMock.Object);
_channelSessionMock.InSequence(seq).Setup(p => p.Open());
_channelSessionMock.InSequence(seq).Setup(p => p.SendExecRequest(_commandText))
.Returns(true)
.Raises(c => c.Closed += null, new ChannelEventArgs(5));
_channelSessionMock.InSequence(seq).Setup(p => p.Dispose());
var asyncResult = _sshCommand.BeginExecute();
_sshCommand.EndExecute(asyncResult);
_channelSessionMock.Verify(p => p.Dispose(), Times.Once);
}
}
}
test/Renci.SshNet.Tests/Classes/SshCommandTest_EndExecute_AsyncResultIsNull.cs
+1 -1
View File
@@ -30,7 +30,7 @@ namespace Renci.SshNet.Tests.Classes
private void Arrange()
{
_sessionMock = new Mock<ISession>(MockBehavior.Strict);
_sessionMock = new Mock<ISession>();
_commandText = new Random().Next().ToString(CultureInfo.InvariantCulture);
_encoding = Encoding.UTF8;
_asyncResult = null;
test/Renci.SshNet.Tests/Classes/SshCommandTest_EndExecute_ChannelOpen.cs
-6
View File
@@ -81,12 +81,6 @@ namespace Renci.SshNet.Tests.Classes
_actual = _sshCommand.EndExecute(_asyncResult);
}
[TestMethod]
public void ChannelSessionShouldBeDisposedOnce()
{
_channelSessionMock.Verify(p => p.Dispose(), Times.Once);
}
[TestMethod]
public void EndExecuteShouldReturnAllDataReceivedInSpecifiedEncoding()
{