On Sat, Dec 14, 2024 at 6:26 AM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote:
>
> On 12/13/24 6:42 AM, Jason Xing wrote:
> >>>> I just noticed a trickier one, sockops bpf prog can write to sk->sk_txhash. The
> >>>> same should go for reading from sk. Also, sockops prog assumes a fullsock sk is
> >>>> a tcp_sock which also won't work for the udp case. A quick thought is to do
> >>>> something similar to is_fullsock. May be repurpose the is_fullsock somehow or a
> >>>> new u8 is needed. Take a look at SOCK_OPS_{GET,SET}_FIELD. It avoids
> >>>> writing/reading the sk when is_fullsock is false.
>
> May be this message buried in the earlier reply or some piece was not clear, so
> worth to highlight here.
>
> Take a look at how is_fullsock is used in SOCK_OPS_{GET,SET}_FIELD. I think a
> similar idea can be borrowed here.
>
> >>>
> >>> Do you mean that if we introduce a new field, then bpf prog can
> >>> read/write the socket?
> >>
> >> The same goes for writing the sk, e.g. writing the sk->sk_txhash. It needs the
> >> sk_lock held. Reading may be ok-ish. The bpf prog can read it anyway by
> >> bpf_probe_read...etc.
> >>
> >> When adding udp timestamp callback later, it needs to stop reading the tcp_sock
> >> through skops from the udp callback for sure. Do take a look at
> >> SOCK_OPS_GET_TCP_SOCK_FIELD. I think we need to ensure the udp timestamp
> >> callback won't break here before moving forward.
> >
> > Agreed. Removing the "sock_ops.sk = sk;" is simple, but I still want
> > the bpf prog to be able to read some fields from the socket under
> > those new callbacks.
>
> No need to remove "sock_ops.sk = sk;". Try to borrow the is_fullsock idea.
>
> Overall, the new timestamp callback breaks assumptions like, sk_lock is held and
> is_fullsock must be a tcp_sock. This needs to be audited. In particular, please
> check sock_ops_func_proto() for all accessible bpf helpers. Also check the
> sock_ops_is_valid_access() and sock_ops_convert_ctx_access() for directly
> accessible fields without the helpers. In particular, the BPF_WRITE (able)
> fields and the tcp_sock fields.
Thanks for the valuable information. I will dig into them.
