netdev - Re: [PATCH net-next] net: devmem: drop iterator type check

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Message-ID: <aCtDMJDtP0DxUBqj@mini-arch>
Date: Mon, 19 May 2025 07:41:52 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, horms@...nel.org,
	sagi@...mberg.me, willemb@...gle.com, almasrymina@...gle.com,
	kaiyuanz@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: devmem: drop iterator type check

On 05/19, Pavel Begunkov wrote:
> On 5/16/25 23:54, Stanislav Fomichev wrote:
> > sendmsg() with a single iov becomes ITER_UBUF, sendmsg() with multiple
> > iovs becomes ITER_IOVEC. Instead of adjusting the check to include
> > ITER_UBUF, drop the check completely. The callers are guaranteed
> > to happen from system call side and we don't need to pay runtime
> > cost to verify it.
> 
> I asked for this because io_uring can pass bvecs. Only sendzc can
> pass that with cmsg, so probably you won't be able to hit any
> real issue, but io_uring needs and soon will have bvec support for
> normal sends as well. One can argue we should care as it isn't
> merged yet, but there is something very very wrong if an unrelated
> and legal io_uring change is able to open a vulnerability in the
> devmem path.

Any reason not to filter these out on the io_uring side? Or you'll
have to interpret sendmsg flags again which is not nice?