tcp: fix sock skb accounting in tcp_read_skb()

Before commit 965b57b469a5 ("net: Introduce a new proto_ops
->read_skb()"), skb was not dequeued from receive queue hence
when we close TCP socket skb can be just flushed synchronously.

After this commit, we have to uncharge skb immediately after being
dequeued, otherwise it is still charged in the original sock. And we
still need to retain skb->sk, as eBPF programs may extract sock
information from skb->sk. Therefore, we have to call
skb_set_owner_sk_safe() here.

Fixes: 965b57b469a5 ("net: Introduce a new proto_ops ->read_skb()")
Reported-and-tested-by: [e-mail]
Tested-by: Stanislav Fomichev <[e-mail]>
Cc: Eric Dumazet <[e-mail]>
Cc: John Fastabend <[e-mail]>
Cc: Jakub Sitnicki <[e-mail]>
Signed-off-by: Cong Wang <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

net/ipv4/tcp.c

···
 		int used;
 
 		__skb_unlink(skb, &sk->sk_receive_queue);
+		WARN_ON(!skb_set_owner_sk_safe(skb, sk));
 		used = recv_actor(sk, skb);
 		if (used <= 0) {
 			if (!copied)