/// <summary>
/// Attempts to connect to the specified process.
/// </summary>
private NamedPipeClientStream TryConnectToProcess(int nodeProcessId, int timeout, long hostHandshake, long clientHandshake)
{
// Try and connect to the process.
string pipeName = "MSBuild" + nodeProcessId;
NamedPipeClientStream nodeStream = new NamedPipeClientStream(".", pipeName, PipeDirection.InOut, PipeOptions.Asynchronous);
CommunicationsUtilities.Trace("Attempting connect to PID {0} with pipe {1} with timeout {2} ms", nodeProcessId, pipeName, timeout);
try
{
nodeStream.Connect(timeout);
// Verify that the owner of the pipe is us. This prevents a security hole where a remote node has
// been faked up with ACLs that would let us attach to it. It could then issue fake build requests back to
// us, potentially causing us to execute builds that do harmful or unexpected things. The pipe owner can
// only be set to the user's own SID by a normal, unprivileged process. The conditions where a faked up
// remote node could set the owner to something else would also let it change owners on other objects, so
// this would be a security flaw upstream of us.
SecurityIdentifier identifier = WindowsIdentity.GetCurrent().Owner;
PipeSecurity remoteSecurity = nodeStream.GetAccessControl();
IdentityReference remoteOwner = remoteSecurity.GetOwner(typeof(SecurityIdentifier));
if (remoteOwner != identifier)
{
CommunicationsUtilities.Trace("The remote pipe owner {0} does not match {1}", remoteOwner.Value, identifier.Value);
throw new UnauthorizedAccessException();
}
CommunicationsUtilities.Trace("Writing handshake to pipe {0}", pipeName);
#if true
nodeStream.WriteLongForHandshake(hostHandshake);
#else
// When the 4th and subsequent node start up, we see this taking a long period of time (0.5s or greater.) This is strictly for debugging purposes.
DateTime writeStart = DateTime.UtcNow;
nodeStream.WriteLong(HostHandshake);
DateTime writeEnd = DateTime.UtcNow;
Console.WriteLine("Node ProcessId {0} WriteLong {1}", nodeProcessId, (writeEnd - writeStart).TotalSeconds);
#endif
CommunicationsUtilities.Trace("Reading handshake from pipe {0}", pipeName);
long handshake = nodeStream.ReadLongForHandshake();
if (handshake != clientHandshake)
{
CommunicationsUtilities.Trace("Handshake failed. Received {0} from client not {1}. Probably the client is a different MSBuild build.", handshake, clientHandshake);
throw new InvalidOperationException();
}
// We got a connection.
CommunicationsUtilities.Trace("Successfully connected to pipe {0}...!", pipeName);
return nodeStream;
}
catch (Exception e)
{
if (ExceptionHandling.IsCriticalException(e))
{
throw;
}
// Can be:
// UnauthorizedAccessException -- Couldn't connect, might not be a node.
// IOException -- Couldn't connect, already in use.
// TimeoutException -- Couldn't connect, might not be a node.
// InvalidOperationException – Couldn’t connect, probably a different build
CommunicationsUtilities.Trace("Failed to connect to pipe {0}. {1}", pipeName, e.Message.TrimEnd());
// If we don't close any stream, we might hang up the child
if (nodeStream != null)
{
nodeStream.Close();
}
}
return null;
}