Re: [PATCH bpf-next v5 2/5] bpf: Add ksock kfuncs

[Mahe Tardy <mahe.tardy@gmail.com>]

On Mon, Aug 10, 2026 at 09:24:38PM -0700, Kuniyuki Iwashima wrote:
> On Fri, Aug 7, 2026 at 10:15 AM Mahe Tardy <mahe.tardy@gmail.com> wrote:
> >
> > Add BPF kfuncs that allow BPF LSM programs to create and use sockets for
> > sending data. This provides a mechanism for BPF programs to emit
> > telemetry. For this first patch set, it's restricted to SOCK_DGRAM
> > socket types with IPPROTO_UDP protocol but could be easily extended to
> > SOCK_STREAM and IPPROTO_TCP in the future.
> >
> > The API consists of five kfuncs:
> >
> >   bpf_ksock_create()   - Create a socket (sleepable)
> >   bpf_ksock_connect()  - Connect socket to remote address (sleepable)
> >   bpf_ksock_send()     - Send data through the socket (sleepable)
> >   bpf_ksock_acquire()  - Acquire a reference to a socket context
> >   bpf_ksock_release()  - Release a reference (cleanup via
> >                          queue_rcu_work since sock_release sleeps)
> >

[...]

> > +
> > +/**
> > + * struct bpf_ksock - refcounted BPF kernel socket context
> > + * @sock:      The underlying kernel socket.
> > + * @usage:     Reference counter.
> > + * @rwork:     RCU work for deferred cleanup (sock_release may sleep).
> > + */
> > +struct bpf_ksock {
> > +       struct socket *sock;
> > +       refcount_t usage;
> > +       struct rcu_work rwork;
> > +};
> > +
> > +static void ksock_release_work_fn(struct work_struct *work)
> > +{
> > +       struct bpf_ksock *ks =
> > +               container_of(to_rcu_work(work), struct bpf_ksock, rwork);
> 
> nit: if you need respin:
> 
> struct bpf_ksock *ks;
> 
> ks = container_of(to_rcu_work(work), struct bpf_ksock, rwork);

sure!

> 
> > +
> > +       sock_release(ks->sock);
> > +       kfree(ks);
> > +}
> > +

[...]

> > +__bpf_kfunc struct bpf_ksock *
> > +bpf_ksock_create(const struct bpf_ksock_create_opts *opts, u32 opts__sz,
> > +                int *err__uninit)
> > +{
> > +       struct bpf_ksock_create_opts opts_copy;
> > +       struct bpf_ksock *ks;
> > +       int err;
> > +
> > +       /*
> > +        * sock_create() derives the network namespace, credentials, and cgroup
> > +        * from current. Kernel threads, including BPF workqueue callbacks, do
> > +        * not carry the context of the task that invoked the BPF program.
> > +        */
> > +       if (!bpf_ksock_has_user_task_context()) {
> > +               err = -EOPNOTSUPP;
> > +               goto err_out;
> > +       }
> > +
> > +       if (!opts || opts__sz != sizeof(struct bpf_ksock_create_opts)) {
> > +               err = -EINVAL;
> > +               goto err_out;
> > +       }
> > +
> > +       opts_copy = (struct bpf_ksock_create_opts){
> > +               .family = READ_ONCE(opts->family),
> 
> I'm not sure if we really want to care about such an arch, but
> since you mentioned unaligned access in bpf_ksock_connect(),
> is READ_OCNE() safe here ?

To my understanding, there's no issue regarding alignement here since
these four fields are __u8. The READ_ONCE is only used so that the
compiler does not do smart things like moving load or reloading a field
between time of check and time of use.

> 
> 
> > +               .type = READ_ONCE(opts->type),
> > +               .protocol = READ_ONCE(opts->protocol),
> > +               .reserved = READ_ONCE(opts->reserved),
> > +       };
> > +

[...]