netdev - Re: [RFC PATCH net-next v6 03/13] bpf: stop UDP sock accessing TCP fields in bpf callbacks

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Message-ID: <CAL+tcoAjQFT57wSxcLaVUJJi1qQYYtE7OH2Q+KpZUziB49uBZg@mail.gmail.com>
Date: Tue, 28 Jan 2025 09:34:20 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, dsahern@...nel.org, willemdebruijn.kernel@...il.com, 
	willemb@...gle.com, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, 
	eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev, 
	john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me, 
	haoluo@...gle.com, jolsa@...nel.org, horms@...nel.org, bpf@...r.kernel.org, 
	netdev@...r.kernel.org
Subject: Re: [RFC PATCH net-next v6 03/13] bpf: stop UDP sock accessing TCP
 fields in bpf callbacks

On Sat, Jan 25, 2025 at 8:28 AM Jason Xing <kerneljasonxing@...il.com> wrote:
>
> On Sat, Jan 25, 2025 at 7:41 AM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
> >
> > On 1/20/25 5:28 PM, Jason Xing wrote:
> > > Applying the new member allow_tcp_access in the existing callbacks
> > > where is_fullsock is set to 1 can help us stop UDP socket accessing
> > > struct tcp_sock, or else it could be catastrophe leading to panic.
> > >
> > > For now, those existing callbacks are used only for TCP. I believe
> > > in the short run, we will have timestamping UDP callbacks support.
> >
> > The commit message needs adjustment. UDP is not supported yet, so this change
> > feels like it's unnecessary based on the commit message. However, even without
> > UDP support, the new timestamping callbacks cannot directly write some fields
> > because the sk lock is not held, so this change is needed for TCP timestamping
>
> Thanks and I will revise them. But I still want to say that the
> timestamping callbacks after this series are all under the protection
> of socket lock.

For the record only, I was wrong about the understanding of socket
lock like above because there remains cases where this kind of path,
say, i40e_intr()->i40e_ptp_tx_hwtstamp()->skb_tstamp_tx()->__skb_tstamp_tx(),
will not be protected under the socket lock. With that said, directly
accessing tcp_sock is not safe even if the socket type is TCP.

Thanks,
Jason