Re: [PATCH net-next v3 02/14] net-timestamp: allow two features to work parallelly

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

> > > >>
> > > >> For datagrams (UDP as well as RAW and many non IP protocols), an
> > > >> alternative still needs to be found.
> > >
> > > In udp/raw/..., I don't know how likely is the user space having "cork->tx_flags
> > > & SKBTX_ANY_TSTAMP" set but has neither "READ_ONCE(sk->sk_tsflags) &
> > > SOF_TIMESTAMPING_OPT_ID" nor "cork->flags & IPCORK_TS_OPT_ID" set.
> >
> > This is not something to rely on. OPT_ID was added relatively recently.
> > Older applications, or any that just use the most straightforward API,
> > will not set this.
> >
> > > If it is
> > > unlikely, may be we can just disallow bpf prog from directly setting
> > > skb_shinfo(skb)->tskey for this particular skb.
> > >
> > > For all other cases, in __ip[6]_append_data, directly call a bpf prog and also
> > > pass the kernel decided tskey to the bpf prog.
> > >
> > > The kernel passed tskey could be 0 (meaning the user space has not used it). The
> > > bpf prog can give one for the kernel to use. The bpf prog can store the
> > > sk_tskey_bpf in the bpf_sk_storage now. Meaning no need to add one to the struct
> > > sock. The bpf prog does not have to start from 0 (e.g. start from U32_MAX
> > > instead) if it helps.
> > >
> > > If the kernel passed tskey is not 0, the bpf prog can just use that one
> > > (assuming the user space is doing something sane, like the value in
> > > SCM_TS_OPT_ID won't be jumping back and front between 0 to U32_MAX). I hope this
> > > is very unlikely also (?) but the bpf prog can probably detect this and choose
> > > to ignore this sk.
> >
> > If an applications uses OPT_ID, it is unlikely that they will toggle
> > the feature on and off on a per-packet basis. So in the common case
> > the program could use the user-set counter or use its own if userspace
> > does not enable the feature. In the rare case that an application does
> > intermittently set an OPT_ID, the numbering would be erratic. This
> > does mean that an actively malicious application could mess with admin
> > measurements.
> >
> 
> Sorry, I got lost in this part. What would you recommend I should do
> about OPT_ID in the next move? Should I keep those three OPT_ID
> patches?

I did not offer a suggestion. Just pointed out a constraint.