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: 8520e224f5 ("bpf, cgroups: Fix cgroup v2 fallback on v1/v2 mixed mode")
Fixes: b7a1848e83 ("bpf: add BPF_PROG_TEST_RUN support for flow dissector")
Fixes: 2cb494a36c ("bpf: add tests for direct packet access from CGROUP_SKB")
Reported-by: syzbot+664b58e9a40fbb2cec71@syzkaller.appspotmail.com
Reported-by: syzbot+33f36d0754d4c5c0e102@syzkaller.appspotmail.com
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: syzbot+664b58e9a40fbb2cec71@syzkaller.appspotmail.com
Tested-by: syzbot+33f36d0754d4c5c0e102@syzkaller.appspotmail.com
Link: https://lore.kernel.org/bpf/20210927123921.21535-2-daniel@iogearbox.net

net/bpf/test_run.c

@@ -552,6 +552,12 @@ static void convert_skb_to___skb(struct sk_buff *skb, struct __sk_buff *__skb)
 	__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)
 {
@@ -596,20 +602,19 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 		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;
@@ -682,8 +687,7 @@ out:
 	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;
 }