[PATCH v4 2/2] selftests/bpf: cover stale CB after LWT IP encapsulation
From: Weiming Shi
Date: Mon Sep 21 2026 - 14:42:44 EST
Add compact regression coverage to the existing LWT IP encapsulation
test. Send an IPv4 ping with a Record Route option through an ingress LWT
program which prepends a TTL-one IPv4 header, then observe __icmp_send()
with fentry and verify that the restored protocol control block no longer
contains the inner header's cached option offsets.
Read ctx->cb[0] in the LWT program so the test exercises
bpf_prog_run_save_cb()'s save/restore path before the post-run check.
Link: https://lore.kernel.org/bpf/DLKB3UXOH0IS.1UL8NV9HSJFXG@xxxxxxxxx/
Signed-off-by: Weiming Shi <bestswngs@xxxxxxxxx>
---
.../selftests/bpf/prog_tests/lwt_ip_encap.c | 45 ++++++++++++++++++
.../selftests/bpf/progs/test_lwt_ip_encap.c | 47 +++++++++++++++++++
2 files changed, 92 insertions(+)
diff --git a/tools/testing/selftests/bpf/prog_tests/lwt_ip_encap.c b/tools/testing/selftests/bpf/prog_tests/lwt_ip_encap.c
index 39e8a3b8b6af..14ba33eaeb96 100644
--- a/tools/testing/selftests/bpf/prog_tests/lwt_ip_encap.c
+++ b/tools/testing/selftests/bpf/prog_tests/lwt_ip_encap.c
@@ -686,3 +686,48 @@ void test_lwt_ip_encap_vxlan_ipv6(void)
{
lwt_ip_encap_vxlan(IPV6_ENCAP);
}
+
+void test_lwt_ip_encap_stale_cb(void)
+{
+ char ns1[NETNS_NAME_SIZE] = NETNS_BASE "-1-";
+ char ns2[NETNS_NAME_SIZE] = NETNS_BASE "-2-";
+ char ns3[NETNS_NAME_SIZE] = NETNS_BASE "-3-";
+ struct test_lwt_ip_encap *skel = NULL;
+
+ if (!ASSERT_OK(create_ns(ns1, NETNS_NAME_SIZE), "create ns1"))
+ goto out;
+ if (!ASSERT_OK(create_ns(ns2, NETNS_NAME_SIZE), "create ns2"))
+ goto out;
+ if (!ASSERT_OK(create_ns(ns3, NETNS_NAME_SIZE), "create ns3"))
+ goto out;
+ if (!ASSERT_OK(setup_network(ns1, ns2, ns3, ""), "setup network"))
+ goto out;
+
+ skel = test_lwt_ip_encap__open();
+ if (!ASSERT_OK_PTR(skel, "open"))
+ goto out;
+ bpf_program__set_autoload(skel->progs.bpf_lwt_encap_gre, false);
+ bpf_program__set_autoload(skel->progs.bpf_lwt_encap_gre6, false);
+ bpf_program__set_autoload(skel->progs.bpf_lwt_encap_vxlan, false);
+ bpf_program__set_autoload(skel->progs.bpf_lwt_encap_vxlan6, false);
+ bpf_program__set_autoload(skel->progs.bpf_lwt_encap_stale, false);
+ if (!ASSERT_OK(test_lwt_ip_encap__load(skel), "load"))
+ goto out;
+ if (!ASSERT_OK(test_lwt_ip_encap__attach(skel), "attach"))
+ goto out;
+
+ SYS(out, "ip -n %s route replace %s/32 encap bpf in obj %s sec encap_stale dev veth3",
+ ns2, IP4_ADDR_DST, BPF_FILE);
+ skel->bss->stale_cb_seen = false;
+ skel->bss->stale_cb_cleared = false;
+ SYS_NOFAIL("ip netns exec %s ping -q -R -c 1 -W 1 -I veth1 %s >/dev/null 2>&1",
+ ns1, IP4_ADDR_DST);
+ ASSERT_TRUE(skel->bss->stale_cb_seen, "stale_cb_seen");
+ ASSERT_TRUE(skel->bss->stale_cb_cleared, "stale_cb_cleared");
+
+out:
+ test_lwt_ip_encap__destroy(skel);
+ SYS_NOFAIL("ip netns del %s", ns1);
+ SYS_NOFAIL("ip netns del %s", ns2);
+ SYS_NOFAIL("ip netns del %s", ns3);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_lwt_ip_encap.c b/tools/testing/selftests/bpf/progs/test_lwt_ip_encap.c
index 4a934fccf8f5..8b57c7fb7fa8 100644
--- a/tools/testing/selftests/bpf/progs/test_lwt_ip_encap.c
+++ b/tools/testing/selftests/bpf/progs/test_lwt_ip_encap.c
@@ -1,6 +1,7 @@
// SPDX-License-Identifier: GPL-2.0
#include "vmlinux.h"
#include <string.h>
+#include <bpf/bpf_core_read.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
#include <bpf/bpf_tracing.h>
@@ -10,6 +11,8 @@ struct grehdr {
__be16 protocol;
};
+#define ICMP_TIME_EXCEEDED 11
+
SEC("encap_gre")
int bpf_lwt_encap_gre(struct __sk_buff *skb)
{
@@ -80,6 +83,29 @@ int bpf_lwt_encap_gre6(struct __sk_buff *skb)
return BPF_LWT_REROUTE;
}
+SEC("encap_stale")
+int bpf_lwt_encap_stale(struct __sk_buff *skb)
+{
+ struct iphdr iph = {};
+
+ /* Exercise CB restore before post-run invalidation. */
+ if (skb->cb[0])
+ return BPF_DROP;
+
+ iph.version = 4;
+ iph.ihl = 5;
+ iph.ttl = 1;
+ iph.protocol = IPPROTO_IPIP;
+ iph.tot_len = bpf_htons(skb->len + sizeof(iph));
+ iph.saddr = bpf_htonl(0xac100264); /* 172.16.2.100 */
+ iph.daddr = bpf_htonl(0xac100464); /* 172.16.4.100 */
+
+ if (bpf_lwt_push_encap(skb, BPF_LWT_ENCAP_IP, &iph, sizeof(iph)))
+ return BPF_DROP;
+
+ return BPF_OK;
+}
+
#define VXLAN_PORT 4789
#define VXLAN_FLAGS 0x08000000
#define VXLAN_VNI 1
@@ -194,6 +220,27 @@ volatile const int tgt_ip_version;
__u16 transport_hdr = 0;
__u16 network_hdr = 0;
bool fexit_triggered = false;
+bool stale_cb_cleared = false;
+bool stale_cb_seen = false;
+
+SEC("fentry/__icmp_send")
+int BPF_PROG(fentry_icmp_send, struct sk_buff *skb, int type, int code,
+ __be32 info, const struct inet_skb_parm *parm)
+{
+ struct iphdr *iph;
+
+ if (type != ICMP_TIME_EXCEEDED)
+ return 0;
+
+ iph = (void *)BPF_CORE_READ(skb, head) + BPF_CORE_READ(skb, network_header);
+ if (BPF_CORE_READ(iph, daddr) != bpf_htonl(0xac100464))
+ return 0;
+
+ stale_cb_seen = true;
+ stale_cb_cleared = !BPF_CORE_READ(parm, opt.optlen) &&
+ !BPF_CORE_READ(parm, opt.rr);
+ return 0;
+}
SEC("?fexit/bpf_lwt_push_ip_encap")
int BPF_PROG(fexit_lwt_push_ip_encap, struct sk_buff *skb, void *hdr, u32 len, bool ingress,
--
2.55.0