[bpf-next RFC 6/6] selftests/bpf: add test for bpf_tcp_gen_syncookie

[Petar Penkov <ppenkov.kernel@gmail.com>]

From: Petar Penkov <ppenkov@google.com>

Modify the existing bpf_tcp_check_syncookie test to also generate a
SYN cookie, pass the packet to the kernel, and verify that the two
cookies are the same (and both valid). Since cloned SKBs are skipped
during generic XDP, this test does not issue a SYN cookie when run in
XDP mode. We therefore only check that a valid SYN cookie was issued at
the TC hook.

Additionally, verify that the MSS for that SYN cookie is within
expected range.

Signed-off-by: Petar Penkov <ppenkov@google.com>
---
 .../bpf/progs/test_tcp_check_syncookie_kern.c | 28 +++++++--
 .../bpf/test_tcp_check_syncookie_user.c       | 61 ++++++++++++++++---
 2 files changed, 76 insertions(+), 13 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/test_tcp_check_syncookie_kern.c b/tools/testing/selftests/bpf/progs/test_tcp_check_syncookie_kern.c
index 1ab095bcacd8..229832766f42 100644
--- a/tools/testing/selftests/bpf/progs/test_tcp_check_syncookie_kern.c
+++ b/tools/testing/selftests/bpf/progs/test_tcp_check_syncookie_kern.c
@@ -19,8 +19,8 @@
 struct bpf_map_def SEC("maps") results = {
 	.type = BPF_MAP_TYPE_ARRAY,
 	.key_size = sizeof(__u32),
-	.value_size = sizeof(__u64),
-	.max_entries = 1,
+	.value_size = sizeof(__u32),
+	.max_entries = 3,
 };
 
 static __always_inline void check_syncookie(void *ctx, void *data,
@@ -33,8 +33,10 @@ static __always_inline void check_syncookie(void *ctx, void *data,
 	struct ipv6hdr *ipv6h;
 	struct tcphdr *tcph;
 	int ret;
+	__u32 key_mss = 2;
+	__u32 key_gen = 1;
 	__u32 key = 0;
-	__u64 value = 1;
+	__s64 seq_mss;
 
 	ethh = data;
 	if (ethh + 1 > data_end)
@@ -66,6 +68,8 @@ static __always_inline void check_syncookie(void *ctx, void *data,
 		if (sk->state != BPF_TCP_LISTEN)
 			goto release;
 
+		seq_mss = bpf_tcp_gen_syncookie(sk, ipv4h, sizeof(*ipv4h),
+						tcph, sizeof(*tcph));
 		ret = bpf_tcp_check_syncookie(sk, ipv4h, sizeof(*ipv4h),
 					      tcph, sizeof(*tcph));
 		break;
@@ -95,6 +99,9 @@ static __always_inline void check_syncookie(void *ctx, void *data,
 		if (sk->state != BPF_TCP_LISTEN)
 			goto release;
 
+		seq_mss = bpf_tcp_gen_syncookie(sk, ipv6h, sizeof(*ipv6h),
+						tcph, sizeof(*tcph));
+
 		ret = bpf_tcp_check_syncookie(sk, ipv6h, sizeof(*ipv6h),
 					      tcph, sizeof(*tcph));
 		break;
@@ -103,8 +110,19 @@ static __always_inline void check_syncookie(void *ctx, void *data,
 		return;
 	}
 
-	if (ret == 0)
-		bpf_map_update_elem(&results, &key, &value, 0);
+	if (seq_mss > 0) {
+		__u32 cookie = bpf_ntohl((__u32)seq_mss);
+		__u32 mss = seq_mss >> 32;
+
+		bpf_map_update_elem(&results, &key_gen, &cookie, 0);
+		bpf_map_update_elem(&results, &key_mss, &mss, 0);
+	}
+
+	if (ret == 0) {
+		__u32 cookie = bpf_ntohl(tcph->ack_seq) - 1;
+
+		bpf_map_update_elem(&results, &key, &cookie, 0);
+	}
 
 release:
 	bpf_sk_release(sk);
diff --git a/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c b/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c
index 87829c86c746..f3ff49ceb481 100644
--- a/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c
+++ b/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c
@@ -2,6 +2,7 @@
 // Copyright (c) 2018 Facebook
 // Copyright (c) 2019 Cloudflare
 
+#include <limits.h>
 #include <string.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -77,7 +78,7 @@ static int connect_to_server(int server_fd)
 	return fd;
 }
 
-static int get_map_fd_by_prog_id(int prog_id)
+static int get_map_fd_by_prog_id(int prog_id, bool *xdp)
 {
 	struct bpf_prog_info info = {};
 	__u32 info_len = sizeof(info);
@@ -104,6 +105,8 @@ static int get_map_fd_by_prog_id(int prog_id)
 		goto err;
 	}
 
+	*xdp = info.type == BPF_PROG_TYPE_XDP;
+
 	map_fd = bpf_map_get_fd_by_id(map_ids[0]);
 	if (map_fd < 0)
 		log_err("Failed to get fd by map id %d", map_ids[0]);
@@ -113,18 +116,32 @@ static int get_map_fd_by_prog_id(int prog_id)
 	return map_fd;
 }
 
-static int run_test(int server_fd, int results_fd)
+static int run_test(int server_fd, int results_fd, bool xdp)
 {
 	int client = -1, srv_client = -1;
 	int ret = 0;
 	__u32 key = 0;
-	__u64 value = 0;
+	__u32 key_gen = 1;
+	__u32 key_mss = 2;
+	__u32 value = 0;
+	__u32 value_gen = 0;
+	__u32 value_mss = 0;
 
 	if (bpf_map_update_elem(results_fd, &key, &value, 0) < 0) {
 		log_err("Can't clear results");
 		goto err;
 	}
 
+	if (bpf_map_update_elem(results_fd, &key_gen, &value_gen, 0) < 0) {
+		log_err("Can't clear results");
+		goto err;
+	}
+
+	if (bpf_map_update_elem(results_fd, &key_mss, &value_mss, 0) < 0) {
+		log_err("Can't clear results");
+		goto err;
+	}
+
 	client = connect_to_server(server_fd);
 	if (client == -1)
 		goto err;
@@ -140,8 +157,35 @@ static int run_test(int server_fd, int results_fd)
 		goto err;
 	}
 
-	if (value != 1) {
-		log_err("Didn't match syncookie: %llu", value);
+	if (value == 0) {
+		log_err("Didn't match syncookie: %u", value);
+		goto err;
+	}
+
+	if (bpf_map_lookup_elem(results_fd, &key_gen, &value_gen) < 0) {
+		log_err("Can't lookup result");
+		goto err;
+	}
+
+	if (xdp && value_gen == 0) {
+		// SYN packets do not get passed through generic XDP, skip the
+		// rest of the test.
+		log_err("Did not find SYN cookie at XDP.");
+		goto out;
+	}
+
+	if (bpf_map_lookup_elem(results_fd, &key_mss, &value_mss) < 0) {
+		log_err("Can't lookup result");
+		goto err;
+	}
+
+	if (value != value_gen) {
+		log_err("BPF generated cookie does not match kernel one");
+		goto err;
+	}
+
+	if (value_mss < 536 || value_mss > USHRT_MAX) {
+		log_err("Unexpected MSS retrieved");
 		goto err;
 	}
 
@@ -163,13 +207,14 @@ int main(int argc, char **argv)
 	int server_v6 = -1;
 	int results = -1;
 	int err = 0;
+	bool xdp;
 
 	if (argc < 2) {
 		fprintf(stderr, "Usage: %s prog_id\n", argv[0]);
 		exit(1);
 	}
 
-	results = get_map_fd_by_prog_id(atoi(argv[1]));
+	results = get_map_fd_by_prog_id(atoi(argv[1]), &xdp);
 	if (results < 0) {
 		log_err("Can't get map");
 		goto err;
@@ -194,10 +239,10 @@ int main(int argc, char **argv)
 	if (server_v6 == -1)
 		goto err;
 
-	if (run_test(server, results))
+	if (run_test(server, results, xdp))
 		goto err;
 
-	if (run_test(server_v6, results))
+	if (run_test(server_v6, results, xdp))
 		goto err;
 
 	printf("ok\n");
-- 
2.22.0.510.g264f2c817a-goog