Re: [PATCH bpf-next v4 3/5] selftests/bpf: Add ksock kfunc test

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

On Fri, Aug 07, 2026 at 05:12:21PM +0800, Jiayuan Chen wrote:
> 
> On 8/7/26 2:22 AM, Mahe Tardy wrote:
> > Add
> [...]
> > +
> > +SEC("lsm.s/socket_bind")
> > +int BPF_PROG(ksock_socket_bind, struct socket *sock, struct sockaddr *address,
> > +	     int addrlen, int ret)
> > +{
> > +	struct __ksock_ctx_value *v;
> > +	struct bpf_ksock *ks, *tmp;
> > +	u32 pid = bpf_get_current_pid_tgid() >> 32;
> > +
> > +	if (ret || pid != target_pid)
> > +		return ret;
> > +
> > +	v = ksock_ctx_value_lookup();
> > +	if (!v) {
> > +		send_ret = -ENOENT;
> > +		return ret;
> > +	}
> > +
> > +	ks = NULL;
> > +	bpf_rcu_read_lock();
> > +	tmp = v->ctx;
> > +	if (tmp)
> > +		ks = bpf_ksock_acquire(tmp);
> > +	bpf_rcu_read_unlock();
> > +
> > +	if (!ks) {
> > +		send_ret = -ENOENT;
> > +		return ret;
> > +	}
> > +
> 
> 
> Since bpf_ksock_send() is sleepable, every consumer of the kptr is
> necessarily a sleepable program and thus has to open-code the same
> bpf_rcu_read_lock()/acquire/unlock sequence before each send.
> 
> Given ksock_common.h already wraps the insert side, how about also
> providing the get side, e.g.:
> 
> static inline struct bpf_ksock *ksock_ctx_get(void)
> {
>     struct __ksock_ctx_value *v = ksock_ctx_value_lookup();
>     struct bpf_ksock *ks = NULL, *tmp;
> 
>     if (!v)
>             return NULL;
>     bpf_rcu_read_lock();
>     tmp = v->ctx;
>     if (tmp)
>             ks = bpf_ksock_acquire(tmp);
>     bpf_rcu_read_unlock();
>     return ks;
> }
> 
> These selftests will be the reference everyone copies from, so
> encapsulating the RCU dance here also documents the correct usage.
> 

Yeah good idea, I'll just keep a slightly difference dance using
bpf_kptr_xchg() in the ksock_lsm_verifier.c program because I want the
verifier to bump against bpf_ksock_send() restriction explicitely and
not bpf_ksock_acquire().