On 3/25/26 5:59 AM, Martin KaFai Lau wrote:
On 3/23/26 3:54 AM, Jiayuan Chen wrote:
+void test_tcp_custom_syncookie_protocol_check(void)
+{
+ struct test_tcp_custom_syncookie *skel;
+ struct sockaddr_in tcp_addr, udp_addr;
+ socklen_t addr_len = sizeof(tcp_addr);
+ int tcp_server = -1, udp_client = -1;
+ char buf[32] = "test";
+ int ret;
+
+ if (setup_netns())
+ return;
+
+ skel = test_tcp_custom_syncookie__open_and_load();
+ if (!ASSERT_OK_PTR(skel, "open_and_load"))
+ return;
+ /* Create a TCP listener so the BPF can find a LISTEN socket */
+ tcp_server = start_server(AF_INET, SOCK_STREAM, "127.0.0.1", 0, 0);
+ if (!ASSERT_NEQ(tcp_server, -1, "start tcp_server"))
+ goto destroy_skel;
+
+ ret = getsockname(tcp_server, (struct sockaddr *)&tcp_addr,
&addr_len);
+ if (!ASSERT_OK(ret, "getsockname"))
+ goto close_tcp;
+
+ skel->bss->tcp_listener_port = ntohs(tcp_addr.sin_port);
+ skel->bss->udp_test_port = 9999;
+
+ ret = bpf_program__fd(skel->progs.tcp_custom_syncookie_badproto);
+ if (setup_tc(ret))
+ goto close_tcp;
+
+ udp_client = socket(AF_INET, SOCK_DGRAM, 0);
+ if (!ASSERT_NEQ(udp_client, -1, "udp socket"))
+ goto cleanup_tc;
+
+ memset(&udp_addr, 0, sizeof(udp_addr));
+ udp_addr.sin_family = AF_INET;
+ udp_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+ udp_addr.sin_port = htons(9999);
+
+ ret = sendto(udp_client, buf, sizeof(buf), 0,
+ (struct sockaddr *)&udp_addr, sizeof(udp_addr));
+ ASSERT_EQ(ret, sizeof(buf), "sendto udp");
+
+ /* Wait for TC ingress BPF to process the skb. */
+ kern_sync_rcu();
hmm... is it guaranteed to work? Regardless, it checks the error
returned from bpf_sk_assign_tcp_reqsk(). Maybe bpf_prog_test_run is
simpler?
pw-bot: cr
+
I looked into using bpf_prog_test_run, but it won't work here
because bpf_sk_assign_tcp_reqsk() requires the skb to come from TC ingress
— it checks skb_at_tc_ingress() internally and returns -EINVAL otherwise.
For the synchronization concern, instead of kern_sync_rcu(), I now create
a UDP server bound to the target port and recv() the packet after sendto().
Since the BPF program returns TC_ACT_OK, the packet passes through TC
ingress
and arrives at the UDP socket. The recv() naturally blocks until the BPF
program
has finished processing, so no timing tricks are needed.
