On Wed, Oct 9, 2024 at 9:19 PM Willem de Bruijn
<willemdebruijn.kernel@xxxxxxxxx> wrote:
>
> Jason Xing wrote:
> > On Wed, Oct 9, 2024 at 2:56 AM Willem de Bruijn
> > <willemdebruijn.kernel@xxxxxxxxx> wrote:
> > >
> > > Jason Xing wrote:
> > > > From: Jason Xing <kernelxing@xxxxxxxxxxx>
> > > >
> > > > We can set OPT_ID|OPT_ID_TCP before we initialize the last skb
> > > > from each sendmsg. We only set the socket once like how we use
> > > > setsockopt() with OPT_ID|OPT_ID_TCP flags.
> > > >
> > > > Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx>
> > > > ---
> > > > net/core/skbuff.c | 16 +++++++++++++---
> > > > net/ipv4/tcp.c | 19 +++++++++++++++----
> > > > 2 files changed, 28 insertions(+), 7 deletions(-)
> > > >
> > >
> > > > @@ -491,10 +491,21 @@ static u32 bpf_tcp_tx_timestamp(struct sock *sk)
> > > > if (!(flags & SOF_TIMESTAMPING_TX_RECORD_MASK))
> > > > return 0;
> > > >
> > > > + /* We require users to set both OPT_ID and OPT_ID_TCP flags
> > > > + * together here, or else the key might be inaccurate.
> > > > + */
> > > > + if (flags & SOF_TIMESTAMPING_OPT_ID &&
> > > > + flags & SOF_TIMESTAMPING_OPT_ID_TCP &&
> > > > + !(sk->sk_tsflags & (SOF_TIMESTAMPING_OPT_ID | SOF_TIMESTAMPING_OPT_ID_TCP))) {
> > > > + atomic_set(&sk->sk_tskey, (tcp_sk(sk)->write_seq - copied));
> > > > + sk->sk_tsflags |= (SOF_TIMESTAMPING_OPT_ID | SOF_TIMESTAMPING_OPT_ID_TCP);
> > >
> > > So user and BPF admin conflict on both sk_tsflags and sktskey?
> > >
> > > I think BPF resetting this key, or incrementing it, may break user
> > > expectations.
> >
> > Yes, when it comes to OPT_ID and OPT_ID_TCP, conflict could happen.
> > The reason why I don't use it like BPF_SOCK_OPS_TS_SCHED_OPT_CB flags
> > (which is set along with each last skb) is that OPT_ID logic is a
> > little bit complex. If we want to avoid touching sk_tsflags field in
> > struct sock, we have to re-implement a similiar logic as you've
> > already done in these years.
>
> One option may be to only allow BPF to use sk_tsflags and sk_tskey if
> sk_tsflags is not set by the user, and to fail user access to these
> fields later.
>
> That enforces mutual exclusion between either user or admin
> timestamping.
>
> Of course, it may still break users if BPF is first, but the user
> socket tries to enable it later. So an imperfect solution.
>
> Ideally the two would use separate per socket state. I don't know
> all the options the various BPF hooks may have for this.
Adding a new sk state or skb state is a much clearer way. That is also
what I commented on the patch [0/9]. While waiting for BPF experts'
reply, I keep investigating if there is a good way to add a new field.
Thanks,
Jason
