bpf: net: Set sk_bpf_storage back to NULL for cloned sk

The cloned sk should not carry its parent-listener's sk_bpf_storage.
This patch fixes it by setting it back to NULL.

Fixes: 6ac99e8 ("bpf: Introduce bpf sk local storage")
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

net/core/sock.c

@@ -1850,6 +1850,9 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
 			goto out;
 		}
 		RCU_INIT_POINTER(newsk->sk_reuseport_cb, NULL);
+#ifdef CONFIG_BPF_SYSCALL
+		RCU_INIT_POINTER(newsk->sk_bpf_storage, NULL);
+#endif
 
 		newsk->sk_err	   = 0;
 		newsk->sk_err_soft = 0;