Re: [PATCH bpf-next v2 1/3] bpf: Expose bpf_get_socket_cookie to tracing programs

[Daniel Borkmann]

On 12/4/20 7:56 PM, Daniel Borkmann wrote:
> On 12/3/20 10:33 PM, Florent Revest wrote:
> > This creates a new helper proto because the existing
> > bpf_get_socket_cookie_sock_proto has a ARG_PTR_TO_CTX argument and only
> > works for BPF programs where the context is a sock.
> >
> > This helper could also be useful to other BPF program types such as LSM.
> >
> > Signed-off-by: Florent Revest <revest@xxxxxxxxxx>
> > ---
> >   include/uapi/linux/bpf.h       | 7 +++++++
> >   kernel/trace/bpf_trace.c       | 4 ++++
> >   net/core/filter.c              | 7 +++++++
> >   tools/include/uapi/linux/bpf.h | 7 +++++++
> >   4 files changed, 25 insertions(+)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index c3458ec1f30a..3e0e33c43998 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -1662,6 +1662,13 @@ union bpf_attr {
> >    *     Return
> >    *         A 8-byte long non-decreasing number.
> >    *
> > + * u64 bpf_get_socket_cookie(void *sk)
> > + *     Description
> > + *         Equivalent to **bpf_get_socket_cookie**\ () helper that accepts
> > + *         *sk*, but gets socket from a BTF **struct sock**.
> > + *     Return
> > + *         A 8-byte long non-decreasing number.
>
> I would not mention this here since it's not fully correct and we should avoid users
> taking non-decreasing granted in their progs. The only assumption you can make is
> that it can be considered a unique number. See also [0] with reverse counter..
>
>    [0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=92acdc58ab11af66fcaef485433fde61b5e32fac

One more thought, in case you plan to use this from sleepable context, you would
need to use sock_gen_cookie() variant in the BPF helper instead.