linux-kernel - Re: [PATCH (resend)] Input: MT

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Message-ID: <CAHk-=wg4peLPGB+Lyvdtwxe6nVeprvTbZiO8_=E8-R_M+VyWow@mail.gmail.com>
Date: Mon, 29 Jul 2024 11:41:59 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, Henrik Rydberg <rydberg@...math.org>, 
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH (resend)] Input: MT - limit max slots

On Mon, 29 Jul 2024 at 11:35, Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
>
> What exactly did you do? Limit size of data userspace can request to be
> written? What is the max allowed size then? Can I stick a warning in the
> code to complain when it is "too big"?

Look up MAX_RW_COUNT.

> So does this mean that we should disallow any and all allocations above
> 4k because they can potentially fail, depending on the system state? Or
> maybe we should be resilient and fail gracefully instead?

We are resilient and fail gracefully.

But there's very a limit to that.

Dmitry - none of this is at all new. The kernel has a *lot* of
practical limits. Many of them actually come from very traditional
sources indeed.

Things like NR_OPEN, PATH_MAX, lots of arbitrary limits because arrays
don't get to grow too big. Things that are *so* basic that you don't
even think about them, because you think they are obvious.

In fact, you should start from the assumption that *EVERYTHING* is limited.

So get off your idiotic high horse. The input layer is not so special
that you should say "I can't have any limits".

                Linus