[Sirened]

> that argument can be used to stop the inclusion of any new large functionality in the kernel.

Sure, it could be, but there are shades of gray. Arguing that adding a full fat SMB server to the kernel is not the same thing as suggesting that file systems should be 100% in user space. You and I both know that the threat posed by introducing a large amount of remotely reachable code is not at all the same as that posed by a new kernel filesystem.

The last few decades of arguing about micro vs monolithic have surely convinced everyone that there is a time and a place for both. Yes, embedding the server in the kernel gives us lower latency by eliding a context switch (a few hundred cycles) but this comes at a pretty high cost that we're going to be paying for years to come.

Call me overly dramatic, but ever since the NSO group stuff went public I've been a lot more risk averse when it comes to introducing remote attack surface because we know that these bugs are being used to kill people. Making kernel compromise harder means possibly saving someone's life. Do I think someone is going to die over a ksmbd bug? Probably not. Would I want to be the one that checked in a huge remotely accessible blob of code? No, so I think carefully about what code I put where to minimize the risk.

[tooltower]

Look, I agree with you. Increased attack surface scares me too. I'm just saying that line of argument doesn't persuade the maintainers or the users. We need to find a better way to protect ourselves. And turning off build flags is one way to do that, one that the community has adopted already.

The other point I'll make is that other kernel features scare me far more than this SMB server. Think io_uring, eBPF, or similar systems. Their attack surfaces are far larger, and yet they have become mainstream. Unfortunately, the horse has already left the barn. We need to find better ways to secure our systems. Arguing for fewer features has been tried for decades, and hasn't helped. Not here in the kernel, not in the browser, not anywhere.

I wish the world was easier to secure, but it's not.