Subject: [PATCH net-next 1/2] tcp: add more DROP REASONs in cookie check

From: Jason Xing <[email-masked]>
Date: Sun, 4 Feb 2024 18:45:59 +0800

From: Jason Xing <[email-masked]>

Since the commit 8eba65fa5f06 ("net: tcp: use kfree_skb_reason() for tcp_v{4,6}_do_rcv()")
introduced the drop reason mechanism, this function is always using
NOT_SPECIFIED which is too general and unhelpful to us if we want to track
this part.

Signed-off-by: Jason Xing <[email-masked]>
---
 include/net/dropreason-core.h | 12 ++++++++++++
 include/net/tcp.h             |  3 ++-
 net/ipv4/syncookies.c         | 18 ++++++++++++++----
 net/ipv4/tcp_ipv4.c           |  7 ++++---
 4 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index 6d3a20163260..85a19b883dee 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -6,6 +6,7 @@
 #define DEFINE_DROP_REASON(FN, FNe)	\
 	FN(NOT_SPECIFIED)		\
 	FN(NO_SOCKET)			\
+	FN(NO_REQSK_ALLOC)			\
 	FN(PKT_TOO_SMALL)		\
 	FN(TCP_CSUM)			\
 	FN(SOCKET_FILTER)		\
@@ -43,10 +44,12 @@
 	FN(TCP_FASTOPEN)		\
 	FN(TCP_OLD_ACK)			\
 	FN(TCP_TOO_OLD_ACK)		\
+	FN(COOKIE_NOCHILD)		\
 	FN(TCP_ACK_UNSENT_DATA)		\
 	FN(TCP_OFO_QUEUE_PRUNE)		\
 	FN(TCP_OFO_DROP)		\
 	FN(IP_OUTNOROUTES)		\
+	FN(IP_ROUTEOUTPUTKEY)		\
 	FN(BPF_CGROUP_EGRESS)		\
 	FN(IPV6DISABLED)		\
 	FN(NEIGH_CREATEFAIL)		\
@@ -54,6 +57,7 @@
 	FN(NEIGH_QUEUEFULL)		\
 	FN(NEIGH_DEAD)			\
 	FN(TC_EGRESS)			\
+	FN(SECURITY_HOOK)			\
 	FN(QDISC_DROP)			\
 	FN(CPU_BACKLOG)			\
 	FN(XDP)				\
@@ -107,6 +111,8 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_NOT_SPECIFIED,
 	/** @SKB_DROP_REASON_NO_SOCKET: socket not found */
 	SKB_DROP_REASON_NO_SOCKET,
+	/** @SKB_DROP_REASON_NO_REQSK_ALLOC: request socket allocation failed */
+	SKB_DROP_REASON_NO_REQSK_ALLOC,
 	/** @SKB_DROP_REASON_PKT_TOO_SMALL: packet size is too small */
 	SKB_DROP_REASON_PKT_TOO_SMALL,
 	/** @SKB_DROP_REASON_TCP_CSUM: TCP checksum error */
@@ -243,6 +249,8 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_TCP_OLD_ACK,
 	/** @SKB_DROP_REASON_TCP_TOO_OLD_ACK: TCP ACK is too old */
 	SKB_DROP_REASON_TCP_TOO_OLD_ACK,
+	/** @SKB_DROP_REASON_COOKIE_NOCHILD: no child socket in cookie mode */
+	SKB_DROP_REASON_COOKIE_NOCHILD,
 	/**
 	 * @SKB_DROP_REASON_TCP_ACK_UNSENT_DATA: TCP ACK for data we haven't
 	 * sent yet
@@ -254,6 +262,8 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_TCP_OFO_DROP,
 	/** @SKB_DROP_REASON_IP_OUTNOROUTES: route lookup failed */
 	SKB_DROP_REASON_IP_OUTNOROUTES,
+	/** @SKB_DROP_REASON_IP_ROUTEOUTPUTKEY: route output key failed */
+	SKB_DROP_REASON_IP_ROUTEOUTPUTKEY,
 	/**
 	 * @SKB_DROP_REASON_BPF_CGROUP_EGRESS: dropped by BPF_PROG_TYPE_CGROUP_SKB
 	 * eBPF program
@@ -271,6 +281,8 @@ 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)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 58e65af74ad1..e3b07d2790c4 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -492,7 +492,8 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
 				 struct request_sock *req,
 				 struct dst_entry *dst);
 int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th);
-struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);
+struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
+				 enum skb_drop_reason *reason);
 struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
 					    struct sock *sk, struct sk_buff *skb,
 					    struct tcp_options_received *tcp_opt,
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index be88bf586ff9..9febad3a3150 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -395,7 +395,8 @@ static struct request_sock *cookie_tcp_check(struct net *net, struct sock *sk,
  * Output is listener if incoming packet would not create a child
  *           NULL if memory could not be allocated.
  */
-struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
+struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
+					     enum skb_drop_reason *reason)
 {
 	struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
 	const struct tcphdr *th = tcp_hdr(skb);
@@ -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) {
+		*reason = SKB_DROP_REASON_NO_REQSK_ALLOC;
 		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)) {
+		*reason = SKB_DROP_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)) {
+		*reason = SKB_DROP_REASON_IP_ROUTEOUTPUTKEY;
 		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);
@@ -477,6 +484,9 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	 */
 	if (ret)
 		inet_sk(ret)->cork.fl.u.ip4 = fl4;
+	else
+		*reason = SKB_DROP_REASON_COOKIE_NOCHILD;
+
 out:
 	return ret;
 out_free:
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 0c50c5a32b84..b63b0efa111d 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1846,13 +1846,14 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
 }
 EXPORT_SYMBOL(tcp_v4_syn_recv_sock);
 
-static struct sock *tcp_v4_cookie_check(struct sock *sk, struct sk_buff *skb)
+static struct sock *tcp_v4_cookie_check(struct sock *sk, struct sk_buff *skb,
+			 enum skb_drop_reason *reason)
 {
 #ifdef CONFIG_SYN_COOKIES
 	const struct tcphdr *th = tcp_hdr(skb);
 
 	if (!th->syn)
-		sk = cookie_v4_check(sk, skb);
+		sk = cookie_v4_check(sk, skb, reason);
 #endif
 	return sk;
 }
@@ -1912,7 +1913,7 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
 		goto csum_err;
 
 	if (sk->sk_state == TCP_LISTEN) {
-		struct sock *nsk = tcp_v4_cookie_check(sk, skb);
+		struct sock *nsk = tcp_v4_cookie_check(sk, skb, &reason);
 
 		if (!nsk)
 			goto discard;
-- 
2.37.3