tcp: allow tls to decrypt directly from the tcp rcv queue

Expose TCP rx queue accessor and cleanup, so that TLS can
decrypt directly from the TCP queue. The expectation
is that the caller can access the skb returned from
tcp_recv_skb() and up to inq bytes worth of data (some
of which may be in ->next skbs) and then call
tcp_read_done() when data has been consumed.
The socket lock must be held continuously across
those two operations.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/tcp.h

@@ -673,6 +673,8 @@ void tcp_get_info(struct sock *, struct tcp_info *);
 int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
 		  sk_read_actor_t recv_actor);
 int tcp_read_skb(struct sock *sk, skb_read_actor_t recv_actor);
+struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off);
+void tcp_read_done(struct sock *sk, size_t len);
 
 void tcp_initialize_rcv_mss(struct sock *sk);
 

net/ipv4/tcp.c

@@ -1635,7 +1635,7 @@ static void tcp_eat_recv_skb(struct sock *sk, struct sk_buff *skb)
 	__kfree_skb(skb);
 }
 
-static struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off)
+struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off)
 {
 	struct sk_buff *skb;
 	u32 offset;
@@ -1658,6 +1658,7 @@ static struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off)
 	}
 	return NULL;
 }
+EXPORT_SYMBOL(tcp_recv_skb);
 
 /*
  * This routine provides an alternative to tcp_recvmsg() for routines
@@ -1788,6 +1789,45 @@ int tcp_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 }
 EXPORT_SYMBOL(tcp_read_skb);
 
+void tcp_read_done(struct sock *sk, size_t len)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	u32 seq = tp->copied_seq;
+	struct sk_buff *skb;
+	size_t left;
+	u32 offset;
+
+	if (sk->sk_state == TCP_LISTEN)
+		return;
+
+	left = len;
+	while (left && (skb = tcp_recv_skb(sk, seq, &offset)) != NULL) {
+		int used;
+
+		used = min_t(size_t, skb->len - offset, left);
+		seq += used;
+		left -= used;
+
+		if (skb->len > offset + used)
+			break;
+
+		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
+			tcp_eat_recv_skb(sk, skb);
+			++seq;
+			break;
+		}
+		tcp_eat_recv_skb(sk, skb);
+	}
+	WRITE_ONCE(tp->copied_seq, seq);
+
+	tcp_rcv_space_adjust(sk);
+
+	/* Clean up data we have read: This will do ACK frames. */
+	if (left != len)
+		tcp_cleanup_rbuf(sk, len - left);
+}
+EXPORT_SYMBOL(tcp_read_done);
+
 int tcp_peek_len(struct socket *sock)
 {
 	return tcp_inq(sock->sk);