[PATCH net-next v2 1/2] net: add missing syncookie statistics for BPF custom syncookies

[PATCH net-next v2 1/2] net: add missing syncookie statistics for BPF custom syncookies

[Jiayuan Chen]

1. Replace IS_ENABLED(CONFIG_BPF) with CONFIG_BPF_SYSCALL for
   cookie_bpf_ok() and cookie_bpf_check(). CONFIG_BPF is selected by
   CONFIG_NET unconditionally, so IS_ENABLED(CONFIG_BPF) is always
   true and provides no real guard. CONFIG_BPF_SYSCALL is the correct
   config for BPF program functionality.

2. Remove the CONFIG_BPF_SYSCALL guard around struct bpf_tcp_req_attrs.
   This struct is referenced by bpf_sk_assign_tcp_reqsk() in
   net/core/filter.c which is compiled unconditionally, so wrapping
   the definition in a config guard could cause build failures when
   CONFIG_BPF_SYSCALL=n.

3. Fix mismatched declaration of cookie_bpf_check() between the
   CONFIG_BPF_SYSCALL and stub paths: the real definition takes
   'struct net *net' but the declaration in the header did not.
   Add the net parameter to the declaration and all call sites.

4. Add missing LINUX_MIB_SYNCOOKIESRECV and LINUX_MIB_SYNCOOKIESFAILED
   statistics in cookie_bpf_check(), so that BPF custom syncookie
   validation is accounted for in SNMP counters just like the
   non-BPF path.

Compile-tested with CONFIG_BPF_SYSCALL=y and CONFIG_BPF_SYSCALL
not set.

Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
No functional bug here — CONFIG_BPF is always enabled under
CONFIG_NET, so the existing code compiles and works correctly.
This is a cleanup and improvement, no backport needed.

Added a selftest, suggested by Kuniyuki Iwashima.
---
 include/net/tcp.h     |  7 +++----
 net/ipv4/syncookies.c | 10 +++++++---
 net/ipv6/syncookies.c |  2 +-
 3 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 6156d1d068e1..570a8836c2ba 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -598,7 +598,6 @@ struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
 					    struct tcp_options_received *tcp_opt,
 					    int mss, u32 tsoff);
 
-#if IS_ENABLED(CONFIG_BPF)
 struct bpf_tcp_req_attrs {
 	u32 rcv_tsval;
 	u32 rcv_tsecr;
@@ -612,7 +611,6 @@ struct bpf_tcp_req_attrs {
 	u8 usec_ts_ok;
 	u8 reserved[3];
 };
-#endif
 
 #ifdef CONFIG_SYN_COOKIES
 
@@ -715,13 +713,14 @@ static inline bool cookie_ecn_ok(const struct net *net, const struct dst_entry *
 		dst_feature(dst, RTAX_FEATURE_ECN);
 }
 
-#if IS_ENABLED(CONFIG_BPF)
+#ifdef CONFIG_BPF_SYSCALL
 static inline bool cookie_bpf_ok(struct sk_buff *skb)
 {
 	return skb->sk;
 }
 
-struct request_sock *cookie_bpf_check(struct sock *sk, struct sk_buff *skb);
+struct request_sock *cookie_bpf_check(struct net *net, struct sock *sk,
+				      struct sk_buff *skb);
 #else
 static inline bool cookie_bpf_ok(struct sk_buff *skb)
 {
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index f1474598d2c8..d685631438cb 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -295,8 +295,9 @@ static int cookie_tcp_reqsk_init(struct sock *sk, struct sk_buff *skb,
 	return 0;
 }
 
-#if IS_ENABLED(CONFIG_BPF)
-struct request_sock *cookie_bpf_check(struct sock *sk, struct sk_buff *skb)
+#ifdef CONFIG_BPF_SYSCALL
+struct request_sock *cookie_bpf_check(struct net *net, struct sock *sk,
+				      struct sk_buff *skb)
 {
 	struct request_sock *req = inet_reqsk(skb->sk);
 
@@ -306,6 +307,9 @@ struct request_sock *cookie_bpf_check(struct sock *sk, struct sk_buff *skb)
 	if (cookie_tcp_reqsk_init(sk, skb, req)) {
 		reqsk_free(req);
 		req = NULL;
+		__NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESFAILED);
+	} else {
+		__NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESRECV);
 	}
 
 	return req;
@@ -419,7 +423,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 		goto out;
 
 	if (cookie_bpf_ok(skb)) {
-		req = cookie_bpf_check(sk, skb);
+		req = cookie_bpf_check(net, sk, skb);
 	} else {
 		req = cookie_tcp_check(net, sk, skb);
 		if (IS_ERR(req))
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 4f6f0d751d6c..111d7a41d957 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -190,7 +190,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 		goto out;
 
 	if (cookie_bpf_ok(skb)) {
-		req = cookie_bpf_check(sk, skb);
+		req = cookie_bpf_check(net, sk, skb);
 	} else {
 		req = cookie_tcp_check(net, sk, skb);
 		if (IS_ERR(req))
-- 
2.43.0

[PATCH net-next v2 2/2] selftests/bpf: verify syncookie statistics in tcp_custom_syncookie

[Jiayuan Chen]

Add read_tcpext_snmp() helper to network_helpers which reads a
TcpExt SNMP counter via nstat, and use it in the tcp_custom_syncookie
test to verify that LINUX_MIB_SYNCOOKIESRECV is incremented and
LINUX_MIB_SYNCOOKIESFAILED stays unchanged across a successful
BPF custom syncookie validation.

The delta is captured between start_server() and accept(), which
covers the full SYN/ACK/cookie-check path for one connection.

Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
 tools/testing/selftests/bpf/network_helpers.c | 22 +++++++++++++++++++
 tools/testing/selftests/bpf/network_helpers.h |  1 +
 .../bpf/prog_tests/tcp_custom_syncookie.c     | 20 +++++++++++++++++
 3 files changed, 43 insertions(+)

diff --git a/tools/testing/selftests/bpf/network_helpers.c b/tools/testing/selftests/bpf/network_helpers.c
index b82f572641b7..3388dd5112b6 100644
--- a/tools/testing/selftests/bpf/network_helpers.c
+++ b/tools/testing/selftests/bpf/network_helpers.c
@@ -621,6 +621,28 @@ int get_socket_local_port(int sock_fd)
 	return -1;
 }
 
+int read_tcpext_snmp(const char *name, unsigned long *val)
+{
+	char cmd[128], buf[128];
+	int ret = 0;
+	FILE *f;
+
+	snprintf(cmd, sizeof(cmd),
+		 "nstat -az TcpExt%s | awk '/TcpExt/ {print $2}'", name);
+	f = popen(cmd, "r");
+	if (!f)
+		return -errno;
+
+	if (!fgets(buf, sizeof(buf), f)) {
+		ret = ferror(f) ? -errno : -ENODATA;
+		goto out;
+	}
+	*val = strtoul(buf, NULL, 10);
+out:
+	pclose(f);
+	return ret;
+}
+
 int get_hw_ring_size(char *ifname, struct ethtool_ringparam *ring_param)
 {
 	struct ifreq ifr = {0};
diff --git a/tools/testing/selftests/bpf/network_helpers.h b/tools/testing/selftests/bpf/network_helpers.h
index 79a010c88e11..c53cd781df6e 100644
--- a/tools/testing/selftests/bpf/network_helpers.h
+++ b/tools/testing/selftests/bpf/network_helpers.h
@@ -84,6 +84,7 @@ int make_sockaddr(int family, const char *addr_str, __u16 port,
 		  struct sockaddr_storage *addr, socklen_t *len);
 char *ping_command(int family);
 int get_socket_local_port(int sock_fd);
+int read_tcpext_snmp(const char *name, unsigned long *val);
 int get_hw_ring_size(char *ifname, struct ethtool_ringparam *ring_param);
 int set_hw_ring_size(char *ifname, struct ethtool_ringparam *ring_param);
 
diff --git a/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c b/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
index eaf441dc7e79..6adfb4b892f8 100644
--- a/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
+++ b/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
@@ -91,12 +91,21 @@ static void transfer_message(int sender, int receiver)
 
 static void create_connection(struct test_tcp_custom_syncookie_case *test_case)
 {
+	unsigned long recv_before, recv_after;
+	unsigned long failed_before, failed_after;
 	int server, client, child;
 
 	server = start_server(test_case->family, test_case->type, test_case->addr, 0, 0);
 	if (!ASSERT_NEQ(server, -1, "start_server"))
 		return;
 
+	if (!ASSERT_OK(read_tcpext_snmp("SyncookiesRecv", &recv_before),
+		       "read SyncookiesRecv before"))
+		goto close_server;
+	if (!ASSERT_OK(read_tcpext_snmp("SyncookiesFailed", &failed_before),
+		       "read SyncookiesFailed before"))
+		goto close_server;
+
 	client = connect_to_fd(server, 0);
 	if (!ASSERT_NEQ(client, -1, "connect_to_fd"))
 		goto close_server;
@@ -105,9 +114,20 @@ static void create_connection(struct test_tcp_custom_syncookie_case *test_case)
 	if (!ASSERT_NEQ(child, -1, "accept"))
 		goto close_client;
 
+	if (!ASSERT_OK(read_tcpext_snmp("SyncookiesRecv", &recv_after),
+		       "read SyncookiesRecv after"))
+		goto close_child;
+	if (!ASSERT_OK(read_tcpext_snmp("SyncookiesFailed", &failed_after),
+		       "read SyncookiesFailed after"))
+		goto close_child;
+
+	ASSERT_EQ(recv_after - recv_before, 1, "SyncookiesRecv delta");
+	ASSERT_EQ(failed_after - failed_before, 0, "SyncookiesFailed delta");
+
 	transfer_message(client, child);
 	transfer_message(child, client);
 
+close_child:
 	close(child);
 close_client:
 	close(client);
-- 
2.43.0