Commit ea98b61b authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

tcp: add drop_reason support to tcp_disordered_ack() 



Following patch is adding a new drop_reason to tcp_validate_incoming().

Change tcp_disordered_ack() to not return a boolean anymore,
but a drop reason.

Change its name to tcp_disordered_ack_check()

Refactor tcp_validate_incoming() to ease the code
review of the following patch, and reduce indentation
level.

This patch is a refactor, with no functional change.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarNeal Cardwell <ncardwell@google.com>
Reviewed-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: default avatarJason Xing <kerneljasonxing@gmail.com>
Link: https://patch.msgid.link/20250113135558.3180360-2-edumazet@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 652aac7e

net/ipv4/tcp_input.c

+44 −35
Original line number Diff line number Diff line
@@ -4450,34 +4450,38 @@ static u32 tcp_tsval_replay(const struct sock *sk) 
	return inet_csk(sk)->icsk_rto * 1200 / HZ;

}



static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)

static enum skb_drop_reason tcp_disordered_ack_check(const struct sock *sk,

						     const struct sk_buff *skb)

{

	const struct tcp_sock *tp = tcp_sk(sk);

	const struct tcphdr *th = tcp_hdr(skb);

	u32 seq = TCP_SKB_CB(skb)->seq;

	SKB_DR_INIT(reason, TCP_RFC7323_PAWS);

	u32 ack = TCP_SKB_CB(skb)->ack_seq;

	u32 seq = TCP_SKB_CB(skb)->seq;



	return	/* 1. Pure ACK with correct sequence number. */

		(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&

	/* 1. Is this not a pure ACK ? */

	if (!th->ack || seq != TCP_SKB_CB(skb)->end_seq)

		return reason;



		/* 2. ... and duplicate ACK. */

		ack == tp->snd_una &&

	/* 2. Is its sequence not the expected one ? */

	if (seq != tp->rcv_nxt)

		return reason;



		/* 3. ... and does not update window. */

		!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&

	/* 3. Is this not a duplicate ACK ? */

	if (ack != tp->snd_una)

		return reason;



		/* 4. ... and sits in replay window. */

		(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <=

		tcp_tsval_replay(sk);

}

	/* 4. Is this updating the window ? */

	if (tcp_may_update_window(tp, ack, seq, ntohs(th->window) <<

						tp->rx_opt.snd_wscale))

		return reason;



static inline bool tcp_paws_discard(const struct sock *sk,

				   const struct sk_buff *skb)

{

	const struct tcp_sock *tp = tcp_sk(sk);

	/* 5. Is this not in the replay window ? */

	if ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) >

	    tcp_tsval_replay(sk))

		return reason;



	return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&

	       !tcp_disordered_ack(sk, skb);

	return 0;

}



/* Check segment sequence number for validity.
@@ -5949,23 +5953,28 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb, 
	SKB_DR(reason);



	/* RFC1323: H1. Apply PAWS check first. */

	if (tcp_fast_parse_options(sock_net(sk), skb, th, tp) &&

	    tp->rx_opt.saw_tstamp &&

	    tcp_paws_discard(sk, skb)) {

		if (!th->rst) {

	if (!tcp_fast_parse_options(sock_net(sk), skb, th, tp) ||

	    !tp->rx_opt.saw_tstamp ||

	    tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW))

		goto step1;



	reason = tcp_disordered_ack_check(sk, skb);

	if (!reason)

		goto step1;

	/* Reset is accepted even if it did not pass PAWS. */

	if (th->rst)

		goto step1;

	if (unlikely(th->syn))

		goto syn_challenge;



	NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);

	if (!tcp_oow_rate_limited(sock_net(sk), skb,

				  LINUX_MIB_TCPACKSKIPPEDPAWS,

				  &tp->last_oow_ack_time))

		tcp_send_dupack(sk, skb);

			SKB_DR_SET(reason, TCP_RFC7323_PAWS);

	goto discard;

		}

		/* Reset is accepted even if it did not pass PAWS. */

	}



step1:

	/* Step 1: check sequence number */

	reason = tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);

	if (reason) {