From: Jiayuan Chen <jiayuan.chen@shopee.com>
Add test_tcp_custom_syncookie_protocol_check to verify that
bpf_sk_assign_tcp_reqsk() rejects non-TCP skbs. The test sends a UDP
packet through TC ingress where a BPF program calls
bpf_sk_assign_tcp_reqsk() on it and checks that the kfunc returns an
error. A UDP server recv() is used as synchronization to ensure the
BPF program has finished processing before checking the result.
Without the fix in bpf_sk_assign_tcp_reqsk(), the kfunc succeeds and
attaches a TCP reqsk to the UDP skb, which causes a null pointer
dereference panic when the kernel processes it through the UDP receive
path.
Test result:
./test_progs -a tcp_custom_syncookie_protocol_check -v
setup_netns:PASS:create netns 0 nsec
setup_netns:PASS:ip 0 nsec
write_sysctl:PASS:open sysctl 0 nsec
write_sysctl:PASS:write sysctl 0 nsec
setup_netns:PASS:write_sysctl 0 nsec
test_tcp_custom_syncookie_protocol_check:PASS:open_and_load 0 nsec
setup_tc:PASS:qdisc add dev lo clsact 0 nsec
setup_tc:PASS:filter add dev lo ingress 0 nsec
run_protocol_check:PASS:start tcp_server 0 nsec
run_protocol_check:PASS:start udp_server 0 nsec
run_protocol_check:PASS:connect udp_client 0 nsec
run_protocol_check:PASS:send udp 0 nsec
run_protocol_check:PASS:recv udp 0 nsec
run_protocol_check:PASS:udp_intercepted 0 nsec
run_protocol_check:PASS:assign_ret 0 nsec
#471/1 tcp_custom_syncookie_protocol_check/IPv4 TCP:OK
run_protocol_check:PASS:start tcp_server 0 nsec
run_protocol_check:PASS:start udp_server 0 nsec
run_protocol_check:PASS:connect udp_client 0 nsec
run_protocol_check:PASS:send udp 0 nsec
run_protocol_check:PASS:recv udp 0 nsec
run_protocol_check:PASS:udp_intercepted 0 nsec
run_protocol_check:PASS:assign_ret 0 nsec
#471/2 tcp_custom_syncookie_protocol_check/IPv6 TCP:OK
#471 tcp_custom_syncookie_protocol_check:OK
Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED
Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
---
.../bpf/prog_tests/tcp_custom_syncookie.c | 94 ++++++++++++++-
.../bpf/progs/test_tcp_custom_syncookie.c | 109 ++++++++++++++++++
2 files changed, 199 insertions(+), 4 deletions(-)
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..e46031d0786b 100644
--- a/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
+++ b/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
@@ -5,6 +5,7 @@
#include <sched.h>
#include <stdlib.h>
#include <net/if.h>
+#include <netinet/in.h>
#include "test_progs.h"
#include "cgroup_helpers.h"
@@ -47,11 +48,10 @@ static int setup_netns(void)
return -1;
}
-static int setup_tc(struct test_tcp_custom_syncookie *skel)
+static int setup_tc(int prog_fd)
{
LIBBPF_OPTS(bpf_tc_hook, qdisc_lo, .attach_point = BPF_TC_INGRESS);
- LIBBPF_OPTS(bpf_tc_opts, tc_attach,
- .prog_fd = bpf_program__fd(skel->progs.tcp_custom_syncookie));
+ LIBBPF_OPTS(bpf_tc_opts, tc_attach, .prog_fd = prog_fd);
qdisc_lo.ifindex = if_nametoindex("lo");
if (!ASSERT_OK(bpf_tc_hook_create(&qdisc_lo), "qdisc add dev lo clsact"))
@@ -127,7 +127,7 @@ void test_tcp_custom_syncookie(void)
if (!ASSERT_OK_PTR(skel, "open_and_load"))
return;
- if (setup_tc(skel))
+ if (setup_tc(bpf_program__fd(skel->progs.tcp_custom_syncookie)))
goto destroy_skel;
for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
@@ -145,6 +145,92 @@ void test_tcp_custom_syncookie(void)
destroy_skel:
system("tc qdisc del dev lo clsact");
+ test_tcp_custom_syncookie__destroy(skel);
+}
+
+/* Test: bpf_sk_assign_tcp_reqsk() should reject non-TCP skb.
+ *
+ * Send a UDP packet through TC ingress where a BPF program calls
+ * bpf_sk_assign_tcp_reqsk() on it. The kfunc should return an error
+ * because the skb carries UDP, not TCP.
+ *
+ * TCP and UDP servers share the same port. The BPF program intercepts
+ * the UDP packet, looks up the TCP listener via the dest port, and
+ * attempts to assign a TCP reqsk to the UDP skb.
+ */
+static void run_protocol_check(struct test_tcp_custom_syncookie *skel,
+ int family, const char *addr)
+{
+ int tcp_server = -1, udp_server = -1, udp_client = -1;
+ char buf[32] = "test";
+ int port, ret;
+
+ tcp_server = start_server(family, SOCK_STREAM, addr, 0, 0);
+ if (!ASSERT_NEQ(tcp_server, -1, "start tcp_server"))
+ return;
+
+ port = ntohs(get_socket_local_port(tcp_server));
+
+ /* UDP server on same port for synchronization and port sharing */
+ udp_server = start_server(family, SOCK_DGRAM, addr, port, 0);
+ if (!ASSERT_NEQ(udp_server, -1, "start udp_server"))
+ goto close_tcp;
+
+ skel->bss->udp_intercepted = false;
+ skel->data->assign_ret = -1;
+
+ udp_client = connect_to_fd(udp_server, 0);
+ if (!ASSERT_NEQ(udp_client, -1, "connect udp_client"))
+ goto close_udp_server;
+ ret = send(udp_client, buf, sizeof(buf), 0);
+ if (!ASSERT_EQ(ret, sizeof(buf), "send udp"))
+ goto close_udp_client;
+
+ /* recv() ensures TC ingress BPF has processed the skb */
+ ret = recv(udp_server, buf, sizeof(buf), 0);
+ if (!ASSERT_EQ(ret, sizeof(buf), "recv udp"))
+ goto close_udp_client;
+
+ ASSERT_EQ(skel->bss->udp_intercepted, true, "udp_intercepted");
+
+ /* assign_ret == 0 means kfunc accepted UDP skb (bug).
+ * assign_ret < 0 means kfunc correctly rejected it (fixed).
+ */
+ ASSERT_NEQ(skel->data->assign_ret, 0, "assign_ret");
+
+close_udp_client:
+ close(udp_client);
+close_udp_server:
+ close(udp_server);
+close_tcp:
+ close(tcp_server);
+}
+
+void test_tcp_custom_syncookie_protocol_check(void)
+{
+ struct test_tcp_custom_syncookie *skel;
+ int i;
+
+ if (setup_netns())
+ return;
+
+ skel = test_tcp_custom_syncookie__open_and_load();
+ if (!ASSERT_OK_PTR(skel, "open_and_load"))
+ return;
+
+ if (setup_tc(bpf_program__fd(skel->progs.tcp_custom_syncookie_badproto)))
+ goto destroy_skel;
+
+ for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
+ if (!test__start_subtest(test_cases[i].name))
+ continue;
+
+ run_protocol_check(skel, test_cases[i].family,
+ test_cases[i].addr);
+ }
+
+destroy_skel:
+ system("tc qdisc del dev lo clsact");
test_tcp_custom_syncookie__destroy(skel);
}
diff --git a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
index 7d5293de1952..c4834abea9c5 100644
--- a/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
+++ b/tools/testing/selftests/bpf/progs/test_tcp_custom_syncookie.c
@@ -588,4 +588,113 @@ int tcp_custom_syncookie(struct __sk_buff *skb)
return tcp_handle_ack(&ctx);
}
+/* Test: call bpf_sk_assign_tcp_reqsk() on a UDP skb.
+ * The kfunc should reject it because the skb is not TCP.
+ *
+ * TCP and UDP servers share the same port. The BPF program intercepts
+ * UDP packets, looks up the TCP listener on the same port, and tries
+ * to assign a TCP reqsk to the UDP skb.
+ */
+int assign_ret = -1;
+bool udp_intercepted = false;
+
+static int badproto_lookup_assign(struct __sk_buff *skb, struct udphdr *udp,
+ struct bpf_sock_tuple *tuple, u32 tuple_size)
+{
+ struct bpf_tcp_req_attrs attrs = {};
+ struct bpf_sock *skc;
+ struct sock *sk;
+
+ skc = bpf_skc_lookup_tcp(skb, tuple, tuple_size, -1, 0);
+ if (!skc)
+ return TC_ACT_OK;
+
+ if (skc->state != TCP_LISTEN) {
+ bpf_sk_release(skc);
+ return TC_ACT_OK;
+ }
+
+ sk = (struct sock *)bpf_skc_to_tcp_sock(skc);
+ if (!sk) {
+ bpf_sk_release(skc);
+ return TC_ACT_OK;
+ }
+
+ attrs.mss = 1460;
+ attrs.wscale_ok = 1;
+ attrs.snd_wscale = 7;
+ attrs.rcv_wscale = 7;
+ attrs.sack_ok = 1;
+
+ assign_ret = bpf_sk_assign_tcp_reqsk(skb, sk, &attrs, sizeof(attrs));
+
+ bpf_sk_release(skc);
+ return TC_ACT_OK;
+}
+
+SEC("tc")
+int tcp_custom_syncookie_badproto(struct __sk_buff *skb)
+{
+ void *data = (void *)(long)skb->data;
+ void *data_end = (void *)(long)skb->data_end;
+ struct bpf_sock_tuple tuple = {};
+ struct ethhdr *eth;
+ struct iphdr *iph;
+ struct ipv6hdr *ip6h;
+ struct udphdr *udp;
+
+ eth = (struct ethhdr *)data;
+ if (eth + 1 > data_end)
+ return TC_ACT_OK;
+
+ switch (bpf_ntohs(eth->h_proto)) {
+ case ETH_P_IP:
+ iph = (struct iphdr *)(eth + 1);
+ if (iph + 1 > data_end)
+ return TC_ACT_OK;
+
+ if (iph->protocol != IPPROTO_UDP)
+ return TC_ACT_OK;
+
+ udp = (struct udphdr *)(iph + 1);
+ if (udp + 1 > data_end)
+ return TC_ACT_OK;
+
+ udp_intercepted = true;
+
+ tuple.ipv4.saddr = iph->saddr;
+ tuple.ipv4.daddr = iph->daddr;
+ tuple.ipv4.sport = udp->source;
+ tuple.ipv4.dport = udp->dest;
+
+ return badproto_lookup_assign(skb, udp, &tuple,
+ sizeof(tuple.ipv4));
+ case ETH_P_IPV6:
+ ip6h = (struct ipv6hdr *)(eth + 1);
+ if (ip6h + 1 > data_end)
+ return TC_ACT_OK;
+
+ if (ip6h->nexthdr != IPPROTO_UDP)
+ return TC_ACT_OK;
+
+ udp = (struct udphdr *)(ip6h + 1);
+ if (udp + 1 > data_end)
+ return TC_ACT_OK;
+
+ udp_intercepted = true;
+
+ __builtin_memcpy(tuple.ipv6.saddr, &ip6h->saddr,
+ sizeof(tuple.ipv6.saddr));
+ __builtin_memcpy(tuple.ipv6.daddr, &ip6h->daddr,
+ sizeof(tuple.ipv6.daddr));
+ tuple.ipv6.sport = udp->source;
+ tuple.ipv6.dport = udp->dest;
+
+ return badproto_lookup_assign(skb, udp, &tuple,
+ sizeof(tuple.ipv6));
+ default:
+ return TC_ACT_OK;
+ }
+}
+
char _license[] SEC("license") = "GPL";
--
2.43.0
On 3/27/26 6:38 AM, Jiayuan Chen wrote:
> From: Jiayuan Chen <jiayuan.chen@shopee.com>
>
> Add test_tcp_custom_syncookie_protocol_check to verify that
> bpf_sk_assign_tcp_reqsk() rejects non-TCP skbs. The test sends a UDP
> packet through TC ingress where a BPF program calls
> bpf_sk_assign_tcp_reqsk() on it and checks that the kfunc returns an
> error. A UDP server recv() is used as synchronization to ensure the
> BPF program has finished processing before checking the result.
>
> Without the fix in bpf_sk_assign_tcp_reqsk(), the kfunc succeeds and
> attaches a TCP reqsk to the UDP skb, which causes a null pointer
> dereference panic when the kernel processes it through the UDP receive
> path.
>
> Test result:
>
> ./test_progs -a tcp_custom_syncookie_protocol_check -v
> setup_netns:PASS:create netns 0 nsec
> setup_netns:PASS:ip 0 nsec
> write_sysctl:PASS:open sysctl 0 nsec
> write_sysctl:PASS:write sysctl 0 nsec
> setup_netns:PASS:write_sysctl 0 nsec
> test_tcp_custom_syncookie_protocol_check:PASS:open_and_load 0 nsec
> setup_tc:PASS:qdisc add dev lo clsact 0 nsec
> setup_tc:PASS:filter add dev lo ingress 0 nsec
> run_protocol_check:PASS:start tcp_server 0 nsec
> run_protocol_check:PASS:start udp_server 0 nsec
> run_protocol_check:PASS:connect udp_client 0 nsec
> run_protocol_check:PASS:send udp 0 nsec
> run_protocol_check:PASS:recv udp 0 nsec
> run_protocol_check:PASS:udp_intercepted 0 nsec
> run_protocol_check:PASS:assign_ret 0 nsec
> #471/1 tcp_custom_syncookie_protocol_check/IPv4 TCP:OK
> run_protocol_check:PASS:start tcp_server 0 nsec
> run_protocol_check:PASS:start udp_server 0 nsec
> run_protocol_check:PASS:connect udp_client 0 nsec
> run_protocol_check:PASS:send udp 0 nsec
> run_protocol_check:PASS:recv udp 0 nsec
> run_protocol_check:PASS:udp_intercepted 0 nsec
> run_protocol_check:PASS:assign_ret 0 nsec
> #471/2 tcp_custom_syncookie_protocol_check/IPv6 TCP:OK
> #471 tcp_custom_syncookie_protocol_check:OK
> Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED
>
> Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
> ---
> .../bpf/prog_tests/tcp_custom_syncookie.c | 94 ++++++++++++++-
> .../bpf/progs/test_tcp_custom_syncookie.c | 109 ++++++++++++++++++
> 2 files changed, 199 insertions(+), 4 deletions(-)
>
> 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..e46031d0786b 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
> @@ -5,6 +5,7 @@
> #include <sched.h>
> #include <stdlib.h>
> #include <net/if.h>
> +#include <netinet/in.h>
>
> #include "test_progs.h"
> #include "cgroup_helpers.h"
> @@ -47,11 +48,10 @@ static int setup_netns(void)
> return -1;
> }
>
> -static int setup_tc(struct test_tcp_custom_syncookie *skel)
> +static int setup_tc(int prog_fd)
> {
> LIBBPF_OPTS(bpf_tc_hook, qdisc_lo, .attach_point = BPF_TC_INGRESS);
> - LIBBPF_OPTS(bpf_tc_opts, tc_attach,
> - .prog_fd = bpf_program__fd(skel->progs.tcp_custom_syncookie));
> + LIBBPF_OPTS(bpf_tc_opts, tc_attach, .prog_fd = prog_fd);
>
> qdisc_lo.ifindex = if_nametoindex("lo");
> if (!ASSERT_OK(bpf_tc_hook_create(&qdisc_lo), "qdisc add dev lo clsact"))
> @@ -127,7 +127,7 @@ void test_tcp_custom_syncookie(void)
> if (!ASSERT_OK_PTR(skel, "open_and_load"))
> return;
>
> - if (setup_tc(skel))
> + if (setup_tc(bpf_program__fd(skel->progs.tcp_custom_syncookie)))
> goto destroy_skel;
>
> for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
> @@ -145,6 +145,92 @@ void test_tcp_custom_syncookie(void)
>
> destroy_skel:
> system("tc qdisc del dev lo clsact");
> + test_tcp_custom_syncookie__destroy(skel);
> +}
> +
> +/* Test: bpf_sk_assign_tcp_reqsk() should reject non-TCP skb.
> + *
> + * Send a UDP packet through TC ingress where a BPF program calls
> + * bpf_sk_assign_tcp_reqsk() on it. The kfunc should return an error
> + * because the skb carries UDP, not TCP.
> + *
> + * TCP and UDP servers share the same port. The BPF program intercepts
> + * the UDP packet, looks up the TCP listener via the dest port, and
> + * attempts to assign a TCP reqsk to the UDP skb.
> + */
> +static void run_protocol_check(struct test_tcp_custom_syncookie *skel,
> + int family, const char *addr)
> +{
> + int tcp_server = -1, udp_server = -1, udp_client = -1;
> + char buf[32] = "test";
> + int port, ret;
> +
> + tcp_server = start_server(family, SOCK_STREAM, addr, 0, 0);
> + if (!ASSERT_NEQ(tcp_server, -1, "start tcp_server"))
> + return;
> +
> + port = ntohs(get_socket_local_port(tcp_server));
> +
> + /* UDP server on same port for synchronization and port sharing */
> + udp_server = start_server(family, SOCK_DGRAM, addr, port, 0);
> + if (!ASSERT_NEQ(udp_server, -1, "start udp_server"))
> + goto close_tcp;
> +
> + skel->bss->udp_intercepted = false;
> + skel->data->assign_ret = -1;
assign_ret is init to -1
> +
> + udp_client = connect_to_fd(udp_server, 0);
> + if (!ASSERT_NEQ(udp_client, -1, "connect udp_client"))
> + goto close_udp_server;
>
> + ret = send(udp_client, buf, sizeof(buf), 0);
> + if (!ASSERT_EQ(ret, sizeof(buf), "send udp"))
> + goto close_udp_client;
> +
> + /* recv() ensures TC ingress BPF has processed the skb */
> + ret = recv(udp_server, buf, sizeof(buf), 0);
> + if (!ASSERT_EQ(ret, sizeof(buf), "recv udp"))
> + goto close_udp_client;
> +
> + ASSERT_EQ(skel->bss->udp_intercepted, true, "udp_intercepted");
> +
> + /* assign_ret == 0 means kfunc accepted UDP skb (bug).
> + * assign_ret < 0 means kfunc correctly rejected it (fixed).
> + */
> + ASSERT_NEQ(skel->data->assign_ret, 0, "assign_ret");
and here it checks NEQ 0....
Maybe init assign_ret to 0?
Also, why not specifically check for -EINVAL?
On 3/28/26 3:53 AM, Martin KaFai Lau wrote:
>> From: Jiayuan Chen <jiayuan.chen@shopee.com>
>>
>> Add test_tcp_custom_syncookie_protocol_check to verify that
>> bpf_sk_assign_tcp_reqsk() rejects non-TCP skbs. The test sends a UDP
>> packet through TC ingress where a BPF program calls
>> bpf_sk_assign_tcp_reqsk() on it and checks that the kfunc returns an
>> error. A UDP server recv() is used as synchronization to ensure the
>> BPF program has finished processing before checking the result.
>>
>> Without the fix in bpf_sk_assign_tcp_reqsk(), the kfunc succeeds and
>> attaches a TCP reqsk to the UDP skb, which causes a null pointer
>> dereference panic when the kernel processes it through the UDP receive
>> path.
>>
>> Test result:
>>
>> ./test_progs -a tcp_custom_syncookie_protocol_check -v
>> setup_netns:PASS:create netns 0 nsec
>> setup_netns:PASS:ip 0 nsec
>> write_sysctl:PASS:open sysctl 0 nsec
>> write_sysctl:PASS:write sysctl 0 nsec
>> setup_netns:PASS:write_sysctl 0 nsec
>> test_tcp_custom_syncookie_protocol_check:PASS:open_and_load 0 nsec
>> setup_tc:PASS:qdisc add dev lo clsact 0 nsec
>> setup_tc:PASS:filter add dev lo ingress 0 nsec
>> run_protocol_check:PASS:start tcp_server 0 nsec
>> run_protocol_check:PASS:start udp_server 0 nsec
>> run_protocol_check:PASS:connect udp_client 0 nsec
>> run_protocol_check:PASS:send udp 0 nsec
>> run_protocol_check:PASS:recv udp 0 nsec
>> run_protocol_check:PASS:udp_intercepted 0 nsec
>> run_protocol_check:PASS:assign_ret 0 nsec
>> #471/1 tcp_custom_syncookie_protocol_check/IPv4 TCP:OK
>> run_protocol_check:PASS:start tcp_server 0 nsec
>> run_protocol_check:PASS:start udp_server 0 nsec
>> run_protocol_check:PASS:connect udp_client 0 nsec
>> run_protocol_check:PASS:send udp 0 nsec
>> run_protocol_check:PASS:recv udp 0 nsec
>> run_protocol_check:PASS:udp_intercepted 0 nsec
>> run_protocol_check:PASS:assign_ret 0 nsec
>> #471/2 tcp_custom_syncookie_protocol_check/IPv6 TCP:OK
>> #471 tcp_custom_syncookie_protocol_check:OK
>> Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED
>>
>> Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
>> Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
>> ---
>> .../bpf/prog_tests/tcp_custom_syncookie.c | 94 ++++++++++++++-
>> .../bpf/progs/test_tcp_custom_syncookie.c | 109 ++++++++++++++++++
>> 2 files changed, 199 insertions(+), 4 deletions(-)
>>
>> 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..e46031d0786b 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/tcp_custom_syncookie.c
>> @@ -5,6 +5,7 @@
>> #include <sched.h>
>> #include <stdlib.h>
>> #include <net/if.h>
>> +#include <netinet/in.h>
>> #include "test_progs.h"
>> #include "cgroup_helpers.h"
>> @@ -47,11 +48,10 @@ static int setup_netns(void)
>> return -1;
>> }
>> -static int setup_tc(struct test_tcp_custom_syncookie *skel)
>> +static int setup_tc(int prog_fd)
>> {
>> LIBBPF_OPTS(bpf_tc_hook, qdisc_lo, .attach_point =
>> BPF_TC_INGRESS);
>> - LIBBPF_OPTS(bpf_tc_opts, tc_attach,
>> - .prog_fd =
>> bpf_program__fd(skel->progs.tcp_custom_syncookie));
>> + LIBBPF_OPTS(bpf_tc_opts, tc_attach, .prog_fd = prog_fd);
>> qdisc_lo.ifindex = if_nametoindex("lo");
>> if (!ASSERT_OK(bpf_tc_hook_create(&qdisc_lo), "qdisc add dev lo
>> clsact"))
>> @@ -127,7 +127,7 @@ void test_tcp_custom_syncookie(void)
>> if (!ASSERT_OK_PTR(skel, "open_and_load"))
>> return;
>> - if (setup_tc(skel))
>> + if (setup_tc(bpf_program__fd(skel->progs.tcp_custom_syncookie)))
>> goto destroy_skel;
>> for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
>> @@ -145,6 +145,92 @@ void test_tcp_custom_syncookie(void)
>> destroy_skel:
>> system("tc qdisc del dev lo clsact");
>> + test_tcp_custom_syncookie__destroy(skel);
>> +}
>> +
>> +/* Test: bpf_sk_assign_tcp_reqsk() should reject non-TCP skb.
>> + *
>> + * Send a UDP packet through TC ingress where a BPF program calls
>> + * bpf_sk_assign_tcp_reqsk() on it. The kfunc should return an error
>> + * because the skb carries UDP, not TCP.
>> + *
>> + * TCP and UDP servers share the same port. The BPF program intercepts
>> + * the UDP packet, looks up the TCP listener via the dest port, and
>> + * attempts to assign a TCP reqsk to the UDP skb.
>> + */
>> +static void run_protocol_check(struct test_tcp_custom_syncookie *skel,
>> + int family, const char *addr)
>> +{
>> + int tcp_server = -1, udp_server = -1, udp_client = -1;
>> + char buf[32] = "test";
>> + int port, ret;
>> +
>> + tcp_server = start_server(family, SOCK_STREAM, addr, 0, 0);
>> + if (!ASSERT_NEQ(tcp_server, -1, "start tcp_server"))
>> + return;
>> +
>> + port = ntohs(get_socket_local_port(tcp_server));
>> +
>> + /* UDP server on same port for synchronization and port sharing */
>> + udp_server = start_server(family, SOCK_DGRAM, addr, port, 0);
>> + if (!ASSERT_NEQ(udp_server, -1, "start udp_server"))
>> + goto close_tcp;
>> +
>> + skel->bss->udp_intercepted = false;
>> + skel->data->assign_ret = -1;
>
> assign_ret is init to -1
>
>> +
>> + udp_client = connect_to_fd(udp_server, 0);
>> + if (!ASSERT_NEQ(udp_client, -1, "connect udp_client"))
>> + goto close_udp_server;
>> + ret = send(udp_client, buf, sizeof(buf), 0);
>> + if (!ASSERT_EQ(ret, sizeof(buf), "send udp"))
>> + goto close_udp_client;
>> +
>> + /* recv() ensures TC ingress BPF has processed the skb */
>> + ret = recv(udp_server, buf, sizeof(buf), 0);
>> + if (!ASSERT_EQ(ret, sizeof(buf), "recv udp"))
>> + goto close_udp_client;
>> +
>> + ASSERT_EQ(skel->bss->udp_intercepted, true, "udp_intercepted");
>> +
>> + /* assign_ret == 0 means kfunc accepted UDP skb (bug).
>> + * assign_ret < 0 means kfunc correctly rejected it (fixed).
>> + */
>> + ASSERT_NEQ(skel->data->assign_ret, 0, "assign_ret");
>
> and here it checks NEQ 0....
>
> Maybe init assign_ret to 0?
>
> Also, why not specifically check for -EINVAL?
You're right, checking for -EINVAL is more precise and avoids hiding a
silent failure in the lookup path.
Will init assign_ret to 0 and check for -EINVAL instead.
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