Re: [PATCH 0/3] vmsplice: make vmsplice a trivial wrapper for preadv2/pwritev2

On Wed, 3 Jun 2026 at 15:23, Andy Lutomirski <[email protected]> wrote:
>
> So I'm suspicious that you've possibly make bugs much (MUCH) harder to
> exploit, but the underlying awful code and opportunity for bugs is
> still there.  MSG_SPLICE_PAGES is still around, and there is still
> (AFAICS) no actual coherent description of what it means.

I don't disagree. I've only looked at the filesystem side.

The networking side does some odd stuff too (and I did look at some of
that, and had to be edumacated by Jakub on some of the subtler rules
for what skb data sharing is ok and when it's not - really not my
area).

But at least MSG_SPLICE_PAGES should be kernel-internal only
interface, and once you don't share page cache pages with networking
code I think that kneecaps a lot of the attacks.

So that's really the aim here for me - at least _attempting_ to go
"maybe we can just limit splice enough that it doesn't even *matter*
when networking does something odd and questionable".

And it's entirely possible that the current zero-copy "networking gets
direct access to the page cache folios" is a huge and insurmountable
performance requirement for some loads. So the vmsplice patch - and
_particularly_ my suggested "let's try always copying" patch - may
simply be doomed.

But I'd rather try to simplify the splice code by removing complexity
- and possibly then failing and having to revert it and rethink things
- than not even trying.

Because I think splice() is a *cool* feature. It was always *clever*.
I just don't think it's worth the pain it has cause.

And it's been around for a long long time, and after more than two
decades it's still most definitely not _widely_ used.

So that makes it a failure in my book. Sometimes "clever" just isn't
the right thing.

               Linus