fix: protect concurrent map access in port-forward

[mcxiv]

Hi everyone,

I rely on the port-forward feature daily at work to proxy hundreds of HTTP requests to our devices. Until now, “concurrent map read and map write” panics caused the CLI to crash dozens of times per day.

Here's my typical stack trace : mender_portforward_stacktrace.txt

This patch adds sync.RWMutex around both the recvChans and mutexAck maps to eliminate data races on map accesses. During my tests, crashes have dropped from hundreds per day to almost zero under normal load.

I'm not going to lie, I'm stuck now, and would appreciate any help as it overpasses my skills. But at least, I think it's a good start.

Sorry for the comments and new line auto-formatting, I'll fix it and squash my final commit if this get any attention.

Thanks,
Quentin

[kjaskiewiczz]

Thanks for your contribution! We don't have capacity to take care of it atm, so I only labeled it and I hope someone from community can help with this.

[merlin-northern]

Thank you @mcxiv very much for the contribution. I consider it a valid fix of a critical bug. It will be part of the upcoming mender-cli release.

Thank you for your interest in and continued use of Mender. Before I approve and we run all the tests, I think we should create a test case for the error scenario you just fixed. Would you consider creating one, or would you like me to write one?

And last minor nit(s): would you mind signing the commits with your key? And we have to do something about the gocyclo: cmd/portforward_tcp.go:106:1: cyclomatic complexity 21 of func (*TCPPortForwarder).handleRequest is high (> 20) (gocyclo)

Thank you! And I am very sorry was not able to comment earlier and that you waited so long.

[merlin-northern]

Would you consider:

Suggested change

	p.mutexAckLock.RLock()
	if mutex, ok := p.mutexAck[connectionID]; ok {
	mutex.Unlock()
	}
	p.mutexAckLock.RUnlock()
	p.mutexAckLock.RLock()
	mutex, ok := p.mutexAck[connectionID]
	p.mutexAckLock.RUnlock()
	if ok && mutex != nil {
	mutex.Unlock()
	}

you know, I do panic when I see mutexes in the critical section ;-)