bpf, test, cgroup: Use sk_{alloc,free} for test cases

BPF test infra has some hacks in place which kzalloc() a socket and perform
minimum init via sock_net_set() and sock_init_data(). As a result, the sk's
skcd->cgroup is NULL since it didn't go through proper initialization as it
would have been the case from sk_alloc(). Rather than re-adding a NULL test
in sock_cgroup_ptr() just for this, use sk_{alloc,free}() pair for the test
socket. The latter also allows to get rid of the bpf_sk_storage_free() special
case.

Fixes: 8520e224f547 ("bpf, cgroups: Fix cgroup v2 fallback on v1/v2 mixed mode")
Fixes: b7a1848e8398 ("bpf: add BPF_PROG_TEST_RUN support for flow dissector")
Fixes: 2cb494a36c98 ("bpf: add tests for direct packet access from CGROUP_SKB")
Reported-by: [e-mail]
Reported-by: [e-mail]
Signed-off-by: Daniel Borkmann <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Tested-by: [e-mail]
Tested-by: [e-mail]
Link: https://lore.kernel.org/bpf/[e-mail]

net/bpf/test_run.c

···
 	__skb->gso_segs = skb_shinfo(skb)->gso_segs;
 }
 
+static struct proto bpf_dummy_proto = {
+	.name   = "bpf_dummy",
+	.owner  = THIS_MODULE,
+	.obj_size = sizeof(struct sock),
+};
+
 int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 			  union bpf_attr __user *uattr)
 {
···
 		break;
 	}
 
-	sk = kzalloc(sizeof(struct sock), GFP_USER);
+	sk = sk_alloc(net, AF_UNSPEC, GFP_USER, &bpf_dummy_proto, 1);
 	if (!sk) {
 		kfree(data);
 		kfree(ctx);
 		return -ENOMEM;
 	}
-	sock_net_set(sk, net);
 	sock_init_data(NULL, sk);
 
 	skb = build_skb(data, 0);
 	if (!skb) {
 		kfree(data);
 		kfree(ctx);
-		kfree(sk);
+		sk_free(sk);
 		return -ENOMEM;
 	}
 	skb->sk = sk;
···
 	if (dev && dev != net->loopback_dev)
 		dev_put(dev);
 	kfree_skb(skb);
-	bpf_sk_storage_free(sk);
-	kfree(sk);
+	sk_free(sk);
 	kfree(ctx);
 	return ret;
 }