[PATCH bpf-next v11 4/5] selftests/bpf: add bpf_icmp_send recursion test
From: Mahe Tardy <hidden>
Date: 2026-07-09 14:49:17
Also in:
bpf
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [selftests] (test runners & infrastructure), kernel selftest framework, the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Shuah Khan, Linus Torvalds
This test is similar to test_icmp_send_unreach_cgroup but checks that, in case of recursion, meaning that the BPF program calling the kfunc was re-triggered by the icmp_send done by the kfunc, the kfunc will stop early and return -EBUSY. The test attaches to the root cgroup to ensure the ICMP packet generated by the kfunc re-triggers the BPF program. Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com> Reviewed-by: Jordan Rife <redacted> Signed-off-by: Mahe Tardy <redacted> --- .../bpf/prog_tests/icmp_send_kfunc.c | 46 ++++++++++++++++ tools/testing/selftests/bpf/progs/icmp_send.c | 55 +++++++++++++++++++ 2 files changed, 101 insertions(+)
diff --git a/tools/testing/selftests/bpf/prog_tests/icmp_send_kfunc.c b/tools/testing/selftests/bpf/prog_tests/icmp_send_kfunc.c
index bbb3c3d4509c..bb532aa0d158 100644
--- a/tools/testing/selftests/bpf/prog_tests/icmp_send_kfunc.c
+++ b/tools/testing/selftests/bpf/prog_tests/icmp_send_kfunc.c@@ -1,8 +1,10 @@ // SPDX-License-Identifier: GPL-2.0 #include <test_progs.h> #include <network_helpers.h> +#include <cgroup_helpers.h> #include <linux/errqueue.h> #include <poll.h> +#include <unistd.h> #include "icmp_send.skel.h" #define TIMEOUT_MS 1000
@@ -10,6 +12,7 @@ #define ICMP_DEST_UNREACH 3 #define ICMPV6_DEST_UNREACH 1 +#define ICMP_HOST_UNREACH 1 #define ICMP_FRAG_NEEDED 4 #define NR_ICMP_UNREACH 15 #define ICMPV6_REJECT_ROUTE 6
@@ -195,3 +198,46 @@ void test_icmp_send_unreach_cgroup(void) if (cgroup_fd >= 0) close(cgroup_fd); } + +void test_icmp_send_unreach_recursion(void) +{ + struct icmp_send *skel; + int cgroup_fd = -1; + int err; + + err = setup_cgroup_environment(); + if (!ASSERT_OK(err, "setup_cgroup_environment")) + return; + + skel = icmp_send__open_and_load(); + if (!ASSERT_OK_PTR(skel, "skel_open")) + goto cleanup; + + cgroup_fd = get_root_cgroup(); + if (!ASSERT_OK_FD(cgroup_fd, "get_root_cgroup")) + goto cleanup; + + skel->data->target_pid = getpid(); + skel->links.recursion = + bpf_program__attach_cgroup(skel->progs.recursion, cgroup_fd); + if (!ASSERT_OK_PTR(skel->links.recursion, "prog_attach_cgroup")) + goto cleanup; + + trigger_prog_read_icmp_errqueue(skel, ICMP_HOST_UNREACH, AF_INET, + "127.0.0.1"); + + /* + * Because there's recursion involved, the first call will return at + * index 1 since it will return the second, and the second call will + * return at index 0 since it will return the first. + */ + ASSERT_EQ(skel->bss->rec_count, 2, "rec_count"); + ASSERT_EQ(skel->data->rec_kfunc_rets[0], -EBUSY, "kfunc_rets[0]"); + ASSERT_EQ(skel->data->rec_kfunc_rets[1], 0, "kfunc_rets[1]"); + +cleanup: + icmp_send__destroy(skel); + if (cgroup_fd >= 0) + close(cgroup_fd); + cleanup_cgroup_environment(); +}
diff --git a/tools/testing/selftests/bpf/progs/icmp_send.c b/tools/testing/selftests/bpf/progs/icmp_send.c
index 6e1ba539eeb0..c642ccdf9fd5 100644
--- a/tools/testing/selftests/bpf/progs/icmp_send.c
+++ b/tools/testing/selftests/bpf/progs/icmp_send.c@@ -12,6 +12,10 @@ __u16 server_port = 0; int unreach_type = 0; int unreach_code = 0; int kfunc_ret = -1; +int target_pid = -1; + +unsigned int rec_count = 0; +int rec_kfunc_rets[] = { -1, -1 }; SEC("cgroup_skb/egress") int egress(struct __sk_buff *skb)
@@ -65,4 +69,55 @@ int egress(struct __sk_buff *skb) return SK_DROP; } +SEC("cgroup_skb/egress") +int recursion(struct __sk_buff *skb) +{ + void *data = (void *)(long)skb->data; + void *data_end = (void *)(long)skb->data_end; + struct icmphdr *icmph; + struct tcphdr *tcph; + struct iphdr *iph; + int ret; + + if ((bpf_get_current_pid_tgid() >> 32) != target_pid) + return SK_PASS; + + iph = data; + if ((void *)(iph + 1) > data_end || iph->version != 4) + return SK_PASS; + + if (iph->daddr != bpf_htonl(SERVER_IP)) + return SK_PASS; + + if (iph->protocol == IPPROTO_TCP) { + tcph = (void *)iph + iph->ihl * 4; + if ((void *)(tcph + 1) > data_end || + tcph->dest != bpf_htons(server_port)) + return SK_PASS; + } else if (iph->protocol == IPPROTO_ICMP) { + icmph = (void *)iph + iph->ihl * 4; + if ((void *)(icmph + 1) > data_end || + icmph->type != unreach_type || icmph->code != unreach_code) + return SK_PASS; + } else { + return SK_PASS; + } + + /* + * This call will provoke a recursion: the ICMP packet generated by the + * kfunc will re-trigger this program since we are in the root cgroup in + * which the kernel ICMP socket belongs. However when re-entering the + * kfunc, it should return EBUSY. + */ + ret = bpf_icmp_send(skb, unreach_type, unreach_code); + rec_kfunc_rets[rec_count & 1] = ret; + __sync_fetch_and_add(&rec_count, 1); + + /* Let the first ICMP error message pass */ + if (iph->protocol == IPPROTO_ICMP) + return SK_PASS; + + return SK_DROP; +} + char LICENSE[] SEC("license") = "Dual BSD/GPL"; --
2.34.1