Re: [RFC PATCH v3 02/20] tcp: don't allow non-devmem originated ppiov

Mina Almasry
2023-12-19T23:25:03Z

On Tue, Dec 19, 2023 at 1:04 PM David Wei <dw@davidwei.uk> wrote:
>
> From: Pavel Begunkov <asml.silence@gmail.com>
>
> NOT FOR UPSTREAM
>
> There will be more users of struct page_pool_iov, and ppiovs from one
> subsystem must not be used by another. That should never happen for any
> sane application, but we need to enforce it in case of bufs and/or
> malicious users.
>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> Signed-off-by: David Wei <dw@davidwei.uk>
> ---
> net/ipv4/tcp.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 33a8bb63fbf5..9c6b18eebb5b 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2384,6 +2384,13 @@ static int tcp_recvmsg_devmem(const struct sock *sk, const struct sk_buff *skb,
> }
>
> ppiov = skb_frag_page_pool_iov(frag);
> +
> + /* Disallow non devmem owned buffers */
> + if (ppiov->pp->p.memory_provider != PP_MP_DMABUF_DEVMEM) {
> + err = -ENODEV;
> + goto out;
> + }
> +

Instead of this, I maybe recommend modifying the skb->dmabuf flag? My
mental model is that flag means all the frags in the skb are
specifically dmabuf, not general ppiovs or net_iovs. Is it possible to
add skb->io_uring or something?

If that bloats the skb headers, then maybe we need another place to
put this flag. Maybe the [page_pool|net]_iov should declare whether
it's dmabuf or otherwise, and we can check frag[0] and assume all
frags are the same as frag0.

But IMO the page pool internals should not leak into the
implementation of generic tcp stack functions.

> end = start + skb_frag_size(frag);
> copy = end - offset;
>
> --
> 2.39.3
>

--
Thanks,
Mina