Merge branch 'tcp-rcv-drop-reasons'

Jason Xing says:

====================
introduce drop reasons for tcp receive path

When I was debugging the reason about why the skb should be dropped in
syn cookie mode, I found out that this NOT_SPECIFIED reason is too
general. Thus I decided to refine it.

v10
Link: https://lore.kernel.org/netdev/20240223193321.6549-1-kuniyu@amazon.com/
1. fix three nit problems (Kuniyuki)
2. add reviewed-by tag (Kuniyuki)

v9
Link: https://lore.kernel.org/netdev/20240222113003.67558-1-kerneljasonxing@gmail.com/
1. nit: remove one unneeded 'else' (David)
2. add reviewed-by tags (Eric, David)

v8
Link: https://lore.kernel.org/netdev/20240221025732.68157-1-kerneljasonxing@gmail.com/
1. refine part of codes in patch [03/10] and patch [10/10] (Eric)
2. squash patch [11/11] in the last version into patch [10/11] (Eric)
3. add reviewed-by tags (Eric)

v7
Link: https://lore.kernel.org/all/20240219032838.91723-1-kerneljasonxing@gmail.com/
1. fix some misspelled problem (Kuniyuki)
2. remove redundant codes in tcp_v6_do_rcv() (Kuniyuki)
3. add reviewed-by tag in patch [02/11] (Kuniyuki)

v6
Link: https://lore.kernel.org/all/c987d2c79e4a4655166eb8eafef473384edb37fb.camel@redhat.com/
Link: https://lore.kernel.org/all/CAL+tcoAgSjwsmFnDh_Gs9ZgMi-y5awtVx+4VhJPNRADjo7LLSA@mail.gmail.com/
1. Take one case into consideration in tcp_v6_do_rcv(), behave like old
days, or else it will trigger errors (Paolo).
2. Extend NO_SOCKET reason to consider two more reasons for request
socket and child socket.

v5:
Link: https://lore.kernel.org/netdev/20240213134205.8705-1-kerneljasonxing@gmail.com/
Link: https://lore.kernel.org/netdev/20240213140508.10878-1-kerneljasonxing@gmail.com/
1. Use SKB_DROP_REASON_IP_OUTNOROUTES instead of introducing a new
   one (Eric, David)
2. Reuse SKB_DROP_REASON_NOMEM to handle failure of request socket
   allocation (Eric)
3. Reuse NO_SOCKET instead of introducing COOKIE_NOCHILD
4. avoid duplication of these opt_skb tests/actions (Eric)
5. Use new name (TCP_ABORT_ON_DATA) for readability (David)
6. Reuse IP_OUTNOROUTES instead of INVALID_DST (Eric)

---
HISTORY
This series is combined with 2 series sent before suggested by Jakub. So
I'm going to separately write changelogs for each of them.

PATCH 1/11 - 5/11
preivious Link: https://lore.kernel.org/netdev/20240213134205.8705-1-kerneljasonxing@gmail.com/
Summary
1. introduce all the dropreasons we need, [1/11] patch.
2. use new dropreasons in ipv4 cookie check, [2/11],[3/11] patch.
3. use new dropreasons ipv6 cookie check, [4/11],[5/11] patch.

v4:
Link: https://lore.kernel.org/netdev/20240212172302.3f95e454@kernel.org/
1. Fix misspelled name in Kdoc as suggested by Jakub.

v3:
Link: https://lore.kernel.org/all/CANn89iK40SoyJ8fS2U5kp3pDruo=zfQNPL-ppOF+LYaS9z-MVA@mail.gmail.com/
1. Split that patch into some smaller ones as suggested by Eric.

v2:
Link: https://lore.kernel.org/all/20240204104601.55760-1-kerneljasonxing@gmail.com/
1. change the title of 2/2 patch.
2. fix some warnings checkpatch tool showed before.
3. use return value instead of adding more parameters suggested by Eric.

PATCH 6/11 - 11/11
previous Link: https://lore.kernel.org/netdev/20240213140508.10878-1-kerneljasonxing@gmail.com/
v4:
Link: https://lore.kernel.org/netdev/CANn89iJar+H3XkQ8HpsirH7b-_sbFe9NBUdAAO3pNJK3CKr_bg@mail.gmail.com/
Link: https://lore.kernel.org/netdev/20240213131205.4309-1-kerneljasonxing@gmail.com/
Already got rid of @acceptable in tcp_rcv_state_process(), so I need to
remove *TCP_CONNREQNOTACCEPTABLE related codes which I wrote in the v3
series.

v3:
Link: https://lore.kernel.org/all/CANn89iK40SoyJ8fS2U5kp3pDruo=zfQNPL-ppOF+LYaS9z-MVA@mail.gmail.com/
1. Split that patch into some smaller ones as suggested by Eric.

v2:
Link: https://lore.kernel.org/all/20240204104601.55760-1-kerneljasonxing@gmail.com/
1. change the title of 2/2 patch.
2. fix some warnings checkpatch tool showed before.
3. use return value instead of adding more parameters suggested by Eric.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dropreason-core.h

@@ -30,6 +30,7 @@
 	FN(TCP_AOFAILURE)		\
 	FN(SOCKET_BACKLOG)		\
 	FN(TCP_FLAGS)			\
+	FN(TCP_ABORT_ON_DATA)		\
 	FN(TCP_ZEROWINDOW)		\
 	FN(TCP_OLD_DATA)		\
 	FN(TCP_OVERWINDOW)		\
@@ -37,6 +38,7 @@
 	FN(TCP_RFC7323_PAWS)		\
 	FN(TCP_OLD_SEQUENCE)		\
 	FN(TCP_INVALID_SEQUENCE)	\
+	FN(TCP_INVALID_ACK_SEQUENCE)	\
 	FN(TCP_RESET)			\
 	FN(TCP_INVALID_SYN)		\
 	FN(TCP_CLOSE)			\
@@ -54,6 +56,7 @@
 	FN(NEIGH_QUEUEFULL)		\
 	FN(NEIGH_DEAD)			\
 	FN(TC_EGRESS)			\
+	FN(SECURITY_HOOK)		\
 	FN(QDISC_DROP)			\
 	FN(CPU_BACKLOG)			\
 	FN(XDP)				\
@@ -105,7 +108,13 @@ enum skb_drop_reason {
 	SKB_CONSUMED,
 	/** @SKB_DROP_REASON_NOT_SPECIFIED: drop reason is not specified */
 	SKB_DROP_REASON_NOT_SPECIFIED,
-	/** @SKB_DROP_REASON_NO_SOCKET: socket not found */
+	/**
+	 * @SKB_DROP_REASON_NO_SOCKET: no valid socket that can be used.
+	 * Reason could be one of three cases:
+	 * 1) no established/listening socket found during lookup process
+	 * 2) no valid request socket during 3WHS process
+	 * 3) no valid child socket during 3WHS process
+	 */
 	SKB_DROP_REASON_NO_SOCKET,
 	/** @SKB_DROP_REASON_PKT_TOO_SMALL: packet size is too small */
 	SKB_DROP_REASON_PKT_TOO_SMALL,
@@ -197,6 +206,11 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_SOCKET_BACKLOG,
 	/** @SKB_DROP_REASON_TCP_FLAGS: TCP flags invalid */
 	SKB_DROP_REASON_TCP_FLAGS,
+	/**
+	 * @SKB_DROP_REASON_TCP_ABORT_ON_DATA: abort on data, corresponding to
+	 * LINUX_MIB_TCPABORTONDATA
+	 */
+	SKB_DROP_REASON_TCP_ABORT_ON_DATA,
 	/**
 	 * @SKB_DROP_REASON_TCP_ZEROWINDOW: TCP receive window size is zero,
 	 * see LINUX_MIB_TCPZEROWINDOWDROP
@@ -221,13 +235,19 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_TCP_OFOMERGE,
 	/**
 	 * @SKB_DROP_REASON_TCP_RFC7323_PAWS: PAWS check, corresponding to
-	 * LINUX_MIB_PAWSESTABREJECTED
+	 * LINUX_MIB_PAWSESTABREJECTED, LINUX_MIB_PAWSACTIVEREJECTED
 	 */
 	SKB_DROP_REASON_TCP_RFC7323_PAWS,
 	/** @SKB_DROP_REASON_TCP_OLD_SEQUENCE: Old SEQ field (duplicate packet) */
 	SKB_DROP_REASON_TCP_OLD_SEQUENCE,
 	/** @SKB_DROP_REASON_TCP_INVALID_SEQUENCE: Not acceptable SEQ field */
 	SKB_DROP_REASON_TCP_INVALID_SEQUENCE,
+	/**
+	 * @SKB_DROP_REASON_TCP_INVALID_ACK_SEQUENCE: Not acceptable ACK SEQ
+	 * field because ack sequence is not in the window between snd_una
+	 * and snd_nxt
+	 */
+	SKB_DROP_REASON_TCP_INVALID_ACK_SEQUENCE,
 	/** @SKB_DROP_REASON_TCP_RESET: Invalid RST packet */
 	SKB_DROP_REASON_TCP_RESET,
 	/**
@@ -271,6 +291,8 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_NEIGH_DEAD,
 	/** @SKB_DROP_REASON_TC_EGRESS: dropped in TC egress HOOK */
 	SKB_DROP_REASON_TC_EGRESS,
+	/** @SKB_DROP_REASON_SECURITY_HOOK: dropped due to security HOOK */
+	SKB_DROP_REASON_SECURITY_HOOK,
 	/**
 	 * @SKB_DROP_REASON_QDISC_DROP: dropped by qdisc when packet outputting (
 	 * failed to enqueue to current qdisc)

include/net/tcp.h

@@ -348,7 +348,7 @@ void tcp_wfree(struct sk_buff *skb);
 void tcp_write_timer_handler(struct sock *sk);
 void tcp_delack_timer_handler(struct sock *sk);
 int tcp_ioctl(struct sock *sk, int cmd, int *karg);
-int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb);
+enum skb_drop_reason tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb);
 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb);
 void tcp_rcv_space_adjust(struct sock *sk);
 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
@@ -396,8 +396,8 @@ enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *tw,
 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 			   struct request_sock *req, bool fastopen,
 			   bool *lost_race);
-int tcp_child_process(struct sock *parent, struct sock *child,
-		      struct sk_buff *skb);
+enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child,
+				       struct sk_buff *skb);
 void tcp_enter_loss(struct sock *sk);
 void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost, int flag);
 void tcp_clear_retrans(struct tcp_sock *tp);

net/ipv4/syncookies.c

@@ -408,6 +408,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	struct rtable *rt;
 	__u8 rcv_wscale;
 	int full_space;
+	SKB_DR(reason);
 
 	if (!READ_ONCE(net->ipv4.sysctl_tcp_syncookies) ||
 	    !th->ack || th->rst)
@@ -420,8 +421,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 		if (IS_ERR(req))
 			goto out;
 	}
-	if (!req)
+	if (!req) {
+		SKB_DR_SET(reason, NO_SOCKET);
 		goto out_drop;
+	}
 
 	ireq = inet_rsk(req);
 
@@ -433,8 +436,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	 */
 	RCU_INIT_POINTER(ireq->ireq_opt, tcp_v4_save_options(net, skb));
 
-	if (security_inet_conn_request(sk, skb, req))
+	if (security_inet_conn_request(sk, skb, req)) {
+		SKB_DR_SET(reason, SECURITY_HOOK);
 		goto out_free;
+	}
 
 	tcp_ao_syncookie(sk, skb, req, AF_INET);
 
@@ -451,8 +456,10 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 			   ireq->ir_loc_addr, th->source, th->dest, sk->sk_uid);
 	security_req_classify_flow(req, flowi4_to_flowi_common(&fl4));
 	rt = ip_route_output_key(net, &fl4);
-	if (IS_ERR(rt))
+	if (IS_ERR(rt)) {
+		SKB_DR_SET(reason, IP_OUTNOROUTES);
 		goto out_free;
+	}
 
 	/* Try to redo what tcp_v4_send_synack did. */
 	req->rsk_window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
@@ -475,12 +482,16 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	/* ip_queue_xmit() depends on our flow being setup
 	 * Normal sockets get it right from inet_csk_route_child_sock()
 	 */
-	if (ret)
-		inet_sk(ret)->cork.fl.u.ip4 = fl4;
+	if (!ret) {
+		SKB_DR_SET(reason, NO_SOCKET);
+		goto out_drop;
+	}
+	inet_sk(ret)->cork.fl.u.ip4 = fl4;
 out:
 	return ret;
 out_free:
 	reqsk_free(req);
 out_drop:
+	kfree_skb_reason(skb, reason);
 	return NULL;
 }

net/ipv4/tcp_input.c

@@ -6361,6 +6361,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 				inet_csk_reset_xmit_timer(sk,
 						ICSK_TIME_RETRANS,
 						TCP_TIMEOUT_MIN, TCP_RTO_MAX);
+			SKB_DR_SET(reason, TCP_INVALID_ACK_SEQUENCE);
 			goto reset_and_undo;
 		}
 
@@ -6369,6 +6370,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 			     tcp_time_stamp_ts(tp))) {
 			NET_INC_STATS(sock_net(sk),
 					LINUX_MIB_PAWSACTIVEREJECTED);
+			SKB_DR_SET(reason, TCP_RFC7323_PAWS);
 			goto reset_and_undo;
 		}
 
@@ -6572,7 +6574,8 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 reset_and_undo:
 	tcp_clear_options(&tp->rx_opt);
 	tp->rx_opt.mss_clamp = saved_clamp;
-	return 1;
+	/* we can reuse/return @reason to its caller to handle the exception */
+	return reason;
 }
 
 static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
@@ -6616,7 +6619,8 @@ static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
  *	address independent.
  */
 
-int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
+enum skb_drop_reason
+tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct inet_connection_sock *icsk = inet_csk(sk);
@@ -6632,7 +6636,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 
 	case TCP_LISTEN:
 		if (th->ack)
-			return 1;
+			return SKB_DROP_REASON_TCP_FLAGS;
 
 		if (th->rst) {
 			SKB_DR_SET(reason, TCP_RESET);
@@ -6701,8 +6705,12 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 				  FLAG_NO_CHALLENGE_ACK);
 
 	if ((int)reason <= 0) {
-		if (sk->sk_state == TCP_SYN_RECV)
-			return 1;	/* send one RST */
+		if (sk->sk_state == TCP_SYN_RECV) {
+			/* send one RST */
+			if (!reason)
+				return SKB_DROP_REASON_TCP_OLD_ACK;
+			return -reason;
+		}
 		/* accept old ack during closing */
 		if ((int)reason < 0) {
 			tcp_send_challenge_ack(sk);
@@ -6778,7 +6786,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 		if (READ_ONCE(tp->linger2) < 0) {
 			tcp_done(sk);
 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
-			return 1;
+			return SKB_DROP_REASON_TCP_ABORT_ON_DATA;
 		}
 		if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
 		    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
@@ -6787,7 +6795,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 				tcp_fastopen_active_disable(sk);
 			tcp_done(sk);
 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
-			return 1;
+			return SKB_DROP_REASON_TCP_ABORT_ON_DATA;
 		}
 
 		tmo = tcp_fin_time(sk);
@@ -6852,7 +6860,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
 				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
 				tcp_reset(sk, skb);
-				return 1;
+				return SKB_DROP_REASON_TCP_ABORT_ON_DATA;
 			}
 		}
 		fallthrough;

net/ipv4/tcp_ipv4.c

@@ -1907,7 +1907,6 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
 		return 0;
 	}
 
-	reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	if (tcp_checksum_complete(skb))
 		goto csum_err;
 
@@ -1915,9 +1914,10 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
 		struct sock *nsk = tcp_v4_cookie_check(sk, skb);
 
 		if (!nsk)
-			goto discard;
+			return 0;
 		if (nsk != sk) {
-			if (tcp_child_process(sk, nsk, skb)) {
+			reason = tcp_child_process(sk, nsk, skb);
+			if (reason) {
 				rsk = nsk;
 				goto reset;
 			}
@@ -1926,7 +1926,8 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
 	} else
 		sock_rps_save_rxhash(sk, skb);
 
-	if (tcp_rcv_state_process(sk, skb)) {
+	reason = tcp_rcv_state_process(sk, skb);
+	if (reason) {
 		rsk = sk;
 		goto reset;
 	}
@@ -2275,10 +2276,12 @@ int tcp_v4_rcv(struct sk_buff *skb)
 		if (nsk == sk) {
 			reqsk_put(req);
 			tcp_v4_restore_cb(skb);
-		} else if (tcp_child_process(sk, nsk, skb)) {
-			tcp_v4_send_reset(nsk, skb);
-			goto discard_and_relse;
 		} else {
+			drop_reason = tcp_child_process(sk, nsk, skb);
+			if (drop_reason) {
+				tcp_v4_send_reset(nsk, skb);
+				goto discard_and_relse;
+			}
 			sock_put(sk);
 			return 0;
 		}

net/ipv4/tcp_minisocks.c

@@ -911,11 +911,11 @@ EXPORT_SYMBOL(tcp_check_req);
  * be created.
  */
 
-int tcp_child_process(struct sock *parent, struct sock *child,
-		      struct sk_buff *skb)
+enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child,
+				       struct sk_buff *skb)
 	__releases(&((child)->sk_lock.slock))
 {
-	int ret = 0;
+	enum skb_drop_reason reason = SKB_NOT_DROPPED_YET;
 	int state = child->sk_state;
 
 	/* record sk_napi_id and sk_rx_queue_mapping of child. */
@@ -923,7 +923,7 @@ int tcp_child_process(struct sock *parent, struct sock *child,
 
 	tcp_segs_in(tcp_sk(child), skb);
 	if (!sock_owned_by_user(child)) {
-		ret = tcp_rcv_state_process(child, skb);
+		reason = tcp_rcv_state_process(child, skb);
 		/* Wakeup parent, send SIGIO */
 		if (state == TCP_SYN_RECV && child->sk_state != state)
 			parent->sk_data_ready(parent);
@@ -937,6 +937,6 @@ int tcp_child_process(struct sock *parent, struct sock *child,
 
 	bh_unlock_sock(child);
 	sock_put(child);
-	return ret;
+	return reason;
 }
 EXPORT_SYMBOL(tcp_child_process);

net/ipv6/syncookies.c

@@ -177,6 +177,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 	struct sock *ret = sk;
 	__u8 rcv_wscale;
 	int full_space;
+	SKB_DR(reason);
 
 	if (!READ_ONCE(net->ipv4.sysctl_tcp_syncookies) ||
 	    !th->ack || th->rst)
@@ -189,16 +190,20 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 		if (IS_ERR(req))
 			goto out;
 	}
-	if (!req)
+	if (!req) {
+		SKB_DR_SET(reason, NO_SOCKET);
 		goto out_drop;
+	}
 
 	ireq = inet_rsk(req);
 
 	ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
 	ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
 
-	if (security_inet_conn_request(sk, skb, req))
+	if (security_inet_conn_request(sk, skb, req)) {
+		SKB_DR_SET(reason, SECURITY_HOOK);
 		goto out_free;
+	}
 
 	if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) ||
 	    np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
@@ -235,8 +240,10 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 		security_req_classify_flow(req, flowi6_to_flowi_common(&fl6));
 
 		dst = ip6_dst_lookup_flow(net, sk, &fl6, final_p);
-		if (IS_ERR(dst))
+		if (IS_ERR(dst)) {
+			SKB_DR_SET(reason, IP_OUTNOROUTES);
 			goto out_free;
+		}
 	}
 
 	req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
@@ -256,10 +263,15 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 	ireq->ecn_ok &= cookie_ecn_ok(net, dst);
 
 	ret = tcp_get_cookie_sock(sk, skb, req, dst);
+	if (!ret) {
+		SKB_DR_SET(reason, NO_SOCKET);
+		goto out_drop;
+	}
 out:
 	return ret;
 out_free:
 	reqsk_free(req);
 out_drop:
+	kfree_skb_reason(skb, reason);
 	return NULL;
 }

net/ipv6/tcp_ipv6.c

@@ -1623,7 +1623,6 @@ int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
 	if (np->rxopt.all)
 		opt_skb = skb_clone_and_charge_r(skb, sk);
 
-	reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	if (sk->sk_state == TCP_ESTABLISHED) { /* Fast path */
 		struct dst_entry *dst;
 
@@ -1653,12 +1652,12 @@ int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
 	if (sk->sk_state == TCP_LISTEN) {
 		struct sock *nsk = tcp_v6_cookie_check(sk, skb);
 
-		if (!nsk)
-			goto discard;
-
 		if (nsk != sk) {
-			if (tcp_child_process(sk, nsk, skb))
-				goto reset;
+			if (nsk) {
+				reason = tcp_child_process(sk, nsk, skb);
+				if (reason)
+					goto reset;
+			}
 			if (opt_skb)
 				__kfree_skb(opt_skb);
 			return 0;
@@ -1666,7 +1665,8 @@ int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
 	} else
 		sock_rps_save_rxhash(sk, skb);
 
-	if (tcp_rcv_state_process(sk, skb))
+	reason = tcp_rcv_state_process(sk, skb);
+	if (reason)
 		goto reset;
 	if (opt_skb)
 		goto ipv6_pktoptions;
@@ -1856,10 +1856,12 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
 		if (nsk == sk) {
 			reqsk_put(req);
 			tcp_v6_restore_cb(skb);
-		} else if (tcp_child_process(sk, nsk, skb)) {
-			tcp_v6_send_reset(nsk, skb);
-			goto discard_and_relse;
 		} else {
+			drop_reason = tcp_child_process(sk, nsk, skb);
+			if (drop_reason) {
+				tcp_v6_send_reset(nsk, skb);
+				goto discard_and_relse;
+			}
 			sock_put(sk);
 			return 0;
 		}