[RFC bpf-next v2 3/3] selftests/bpf: Add a test for the PPPoE encap/decap adjust_room flags
From: ThisSeanZhang <hidden>
Date: 2026-10-03 19:34:09
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, Shuah Khan, Linus Torvalds
Add a tc test that exercises the new BPF_F_ADJ_ROOM_ENCAP_PPPOE and BPF_F_ADJ_ROOM_DECAP_PPPOE flags of bpf_skb_adjust_room(). The encap program is run over plain Ethernet/IPv4 and Ethernet/IPv6 packets. The test checks that the PPPoE session header is inserted between the Ethernet and network headers, that the PPP protocol and skb->protocol are correct, and that the payload is preserved. It then runs the decap program and checks that the original packet and protocol metadata are restored. A rejection program exercises calls to bpf_skb_adjust_room() that the helper must reject: an encapsulation length other than PPPOE_SES_HLEN, encapsulation in BPF_ADJ_ROOM_NET mode, a negative encapsulation length, the encap flag combined with a decap flag, shrinking a PPPoE packet without the PPPoE flag, and decapsulation of a packet whose skb->protocol is not ETH_P_PPP_SES. Decapsulation of a PPPoE packet with an unsupported PPP protocol and of a packet too short to still hold an IP header is rejected as well. Signed-off-by: ThisSeanZhang <redacted> --- .../selftests/bpf/prog_tests/tc_pppoe.c | 254 ++++++++++++++++++ tools/testing/selftests/bpf/progs/tc_pppoe.c | 163 +++++++++++ 2 files changed, 417 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/tc_pppoe.c create mode 100644 tools/testing/selftests/bpf/progs/tc_pppoe.c
diff --git a/tools/testing/selftests/bpf/prog_tests/tc_pppoe.c b/tools/testing/selftests/bpf/prog_tests/tc_pppoe.c
new file mode 100644
index 000000000..73e602c91
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/tc_pppoe.c@@ -0,0 +1,254 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 ThisSeanZhang */ + +#include <arpa/inet.h> +#include <test_progs.h> +#include "tc_pppoe.skel.h" + +/* Ethernet + IPv4 + TCP, 54 bytes in total. */ +static const __u8 ip4_pkt[] = { + /* Ethernet header. */ + 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, + 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff, + 0x08, 0x00, + /* IPv4 header. */ + 0x45, 0x00, 0x00, 0x28, + 0x12, 0x34, 0x40, 0x00, + 0x40, 0x06, 0x00, 0x00, + 0xc0, 0xa8, 0x01, 0x01, + 0xc0, 0xa8, 0x01, 0x02, + /* TCP header. */ + 0x00, 0x50, 0x1f, 0x90, + 0x00, 0x00, 0x00, 0x01, + 0x00, 0x00, 0x00, 0x00, + 0x50, 0x02, 0x10, 0x00, + 0x00, 0x00, 0x00, 0x00, +}; + +/* Ethernet + IPv6 + TCP, 74 bytes in total. */ +static const __u8 ip6_pkt[] = { + /* Ethernet header. */ + 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, + 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff, + 0x86, 0xdd, + /* IPv6 header. */ + 0x60, 0x00, 0x00, 0x00, + 0x00, 0x14, 0x06, 0x40, + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, + /* TCP header. */ + 0x00, 0x50, 0x1f, 0x90, + 0x00, 0x00, 0x00, 0x01, + 0x00, 0x00, 0x00, 0x00, + 0x50, 0x02, 0x10, 0x00, + 0x00, 0x00, 0x00, 0x00, +}; + +#define PPP_SES_HLEN 8 +#define TC_ACT_SHOT 2 + +static int run_prog(int prog_fd, const void *data_in, __u32 size_in, + void *data_out, __u32 size_out, __u32 *retval, + __u32 *size_out_actual) +{ + LIBBPF_OPTS(bpf_test_run_opts, opts, + .data_in = (void *)data_in, + .data_size_in = size_in, + .data_out = data_out, + .data_size_out = size_out, + ); + int ret; + + ret = bpf_prog_test_run_opts(prog_fd, &opts); + if (!ret && retval) + *retval = opts.retval; + if (!ret && size_out_actual) + *size_out_actual = opts.data_size_out; + + return ret; +} + +static void test_encap_decap(struct tc_pppoe *skel, const char *subtest, + const __u8 *pkt, __u32 pkt_len, int ethertype, + __u8 ppp_proto) +{ + __u8 encap_pkt[128]; + __u8 decap_pkt[128]; + __u32 retval, out_len; + int ret; + + if (!test__start_subtest(subtest)) + return; + + skel->bss->encap_proto = 0; + ret = run_prog(bpf_program__fd(skel->progs.tc_pppoe_encap), + pkt, pkt_len, encap_pkt, sizeof(encap_pkt), + &retval, &out_len); + ASSERT_OK(ret, "encap test_run"); + ASSERT_OK(retval, "encap retval"); + ASSERT_EQ(out_len, pkt_len + PPP_SES_HLEN, "encap pkt len"); + ASSERT_EQ(skel->bss->encap_proto, htons(0x8864), + "encap skb protocol"); + + /* Ethernet header, with the ethertype changed to PPPoE session. */ + ASSERT_EQ(encap_pkt[12], 0x88, "encap eth h_proto"); + ASSERT_EQ(encap_pkt[13], 0x64, "encap eth h_proto"); + /* + * PPPoE session header: ver/type/code, session id, length and + * PPP protocol. + */ + ASSERT_EQ(encap_pkt[14], 0x11, "encap pppoe ver/type"); + ASSERT_EQ(encap_pkt[15], 0x00, "encap pppoe code"); + ASSERT_EQ(encap_pkt[16], 0xde, "encap pppoe sid"); + ASSERT_EQ(encap_pkt[17], 0xad, "encap pppoe sid"); + ASSERT_EQ(encap_pkt[18], 0x00, "encap pppoe length"); + ASSERT_EQ(encap_pkt[19], pkt_len - 14 + 2, "encap pppoe length"); + ASSERT_EQ(encap_pkt[20], 0x00, "encap ppp proto"); + ASSERT_EQ(encap_pkt[21], ppp_proto, "encap ppp proto"); + /* + * The original packet must be shifted unchanged behind the + * new header. + */ + ASSERT_MEMEQ(encap_pkt + 14 + PPP_SES_HLEN, pkt + 14, + pkt_len - 14, "encap payload"); + + skel->bss->decap_proto = 0; + ret = run_prog(bpf_program__fd(skel->progs.tc_pppoe_decap), + encap_pkt, pkt_len + PPP_SES_HLEN, decap_pkt, + sizeof(decap_pkt), &retval, &out_len); + ASSERT_OK(ret, "decap test_run"); + ASSERT_OK(retval, "decap retval"); + ASSERT_EQ(out_len, pkt_len, "decap pkt len"); + ASSERT_EQ(skel->bss->decap_proto, ethertype, "decap skb protocol"); + ASSERT_MEMEQ(decap_pkt, pkt, pkt_len, "decap packet"); +} + +static void test_reject(struct tc_pppoe *skel, int case_id, + const void *data_in, __u32 size_in, const char *name) +{ + __u8 out[128]; + __u32 retval = 0; + int ret; + + if (!test__start_subtest(name)) + return; + + skel->bss->reject_case = case_id; + skel->bss->reject_unexpected = 0; + ret = run_prog(bpf_program__fd(skel->progs.tc_pppoe_reject), + data_in, size_in, out, sizeof(out), &retval, NULL); + ASSERT_OK(ret, "reject test_run"); + ASSERT_EQ(retval, TC_ACT_SHOT, "helper rejected the call"); + ASSERT_EQ(skel->bss->reject_unexpected, 0, "no unexpected success"); +} + +static void test_decap_reject_input(struct tc_pppoe *skel, + const __u8 *pkt, __u32 pkt_len, + const char *subtest) +{ + __u8 out[128]; + __u32 retval = 0; + int ret; + + if (!test__start_subtest(subtest)) + return; + + skel->bss->decap_proto = 0; + ret = run_prog(bpf_program__fd(skel->progs.tc_pppoe_decap), + pkt, pkt_len, out, sizeof(out), &retval, NULL); + ASSERT_OK(ret, "decap reject test_run"); + ASSERT_EQ(retval, TC_ACT_SHOT, "helper rejected the call"); + ASSERT_EQ(skel->bss->decap_proto, 0, "skb protocol unchanged"); +} + +void test_tc_pppoe(void) +{ + /* + * A PPPoE packet whose PPP protocol is neither IPv4 nor IPv6: + * IP control protocol (0x8021) in this case. + */ + static const __u8 bad_ppp_pkt[] = { + 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, + 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff, + 0x88, 0x64, + 0x11, 0x00, 0x00, 0x00, 0x00, 0x28, 0x80, 0x21, + 0x45, 0x00, 0x00, 0x28, + 0x12, 0x34, 0x40, 0x00, + 0x40, 0x06, 0x00, 0x00, + 0xc0, 0xa8, 0x01, 0x01, + 0xc0, 0xa8, 0x01, 0x02, + 0x00, 0x50, 0x1f, 0x90, + 0x00, 0x00, 0x00, 0x01, + 0x00, 0x00, 0x00, 0x00, + 0x50, 0x02, 0x10, 0x00, + 0x00, 0x00, 0x00, 0x00, + }; + /* + * A PPPoE packet whose payload is too short to still contain a + * full IP header after decapsulation. + */ + static const __u8 truncated_pkt[] = { + 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, + 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff, + 0x88, 0x64, + 0x11, 0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x21, + 0x45, 0x00, + }; + /* Non-PPPoE IPv4 packet whose bytes 20/21 decode as PPP_IP. */ + static const __u8 fake_ppp_pkt[] = { + 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, + 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff, + 0x08, 0x00, + 0x45, 0x00, 0x00, 0x28, + 0x12, 0x34, 0x00, 0x21, + 0x40, 0x06, 0x00, 0x00, + 0xc0, 0xa8, 0x01, 0x01, + 0xc0, 0xa8, 0x01, 0x02, + 0x00, 0x50, 0x1f, 0x90, + 0x00, 0x00, 0x00, 0x01, + 0x00, 0x00, 0x00, 0x00, + 0x50, 0x02, 0x10, 0x00, + 0x00, 0x00, 0x00, 0x00, + }; + __u8 encap_pkt[128]; + struct tc_pppoe *skel; + __u32 retval, out_len; + + skel = tc_pppoe__open_and_load(); + if (!ASSERT_OK_PTR(skel, "skel open_and_load")) + return; + + test_encap_decap(skel, "encap-decap-v4", ip4_pkt, sizeof(ip4_pkt), + htons(0x0800), 0x21); + test_encap_decap(skel, "encap-decap-v6", ip6_pkt, sizeof(ip6_pkt), + htons(0x86dd), 0x57); + + test_decap_reject_input(skel, bad_ppp_pkt, sizeof(bad_ppp_pkt), + "decap-bad-ppp-proto"); + test_decap_reject_input(skel, truncated_pkt, sizeof(truncated_pkt), + "decap-truncated"); + test_reject(skel, 6, fake_ppp_pkt, sizeof(fake_ppp_pkt), + "reject-decap-fake-ppp-proto"); + + /* + * Encapsulate a v4 packet once more to get a PPPoE packet as + * input for the "decap without the flag" rejection case. + */ + ASSERT_OK(run_prog(bpf_program__fd(skel->progs.tc_pppoe_encap), + ip4_pkt, sizeof(ip4_pkt), encap_pkt, + sizeof(encap_pkt), &retval, &out_len), + "encap v4 for reject input"); + + test_reject(skel, 1, ip4_pkt, sizeof(ip4_pkt), "reject-encap-len"); + test_reject(skel, 2, ip4_pkt, sizeof(ip4_pkt), "reject-encap-mode"); + test_reject(skel, 3, ip4_pkt, sizeof(ip4_pkt), "reject-encap-shrink"); + test_reject(skel, 4, ip4_pkt, sizeof(ip4_pkt), "reject-flag-mix"); + test_reject(skel, 5, encap_pkt, sizeof(ip4_pkt) + PPP_SES_HLEN, + "reject-decap-no-flag"); + test_reject(skel, 6, ip4_pkt, sizeof(ip4_pkt), + "reject-decap-non-pppoe"); + + tc_pppoe__destroy(skel); +}
diff --git a/tools/testing/selftests/bpf/progs/tc_pppoe.c b/tools/testing/selftests/bpf/progs/tc_pppoe.c
new file mode 100644
index 000000000..b1624f0f9
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/tc_pppoe.c@@ -0,0 +1,163 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 ThisSeanZhang */ + +#include "vmlinux.h" +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_endian.h> + +#define ETH_P_IP_TEST 0x0800 +#define ETH_P_IPV6_TEST 0x86dd +#define ETH_P_PPP_SES_TEST 0x8864 +#define PPP_IP_TEST 0x21 +#define PPP_IPV6_TEST 0x57 + +#define ETH_HLEN_TEST 14 +#define PPPOE_SES_HLEN_TEST 8 + +#define TC_ACT_OK_TEST 0 +#define TC_ACT_SHOT_TEST 2 + +/* Selects the bpf_skb_adjust_room() call made by tc_pppoe_reject. */ +int reject_case; + +/* skb->protocol as observed after the helper call. */ +int encap_proto; +int decap_proto; + +/* + * Set when tc_pppoe_reject observes a call that should have been + * rejected by the helper. + */ +int reject_unexpected; + +SEC("tc") +int tc_pppoe_encap(struct __sk_buff *skb) +{ + __u8 hdr[PPPOE_SES_HLEN_TEST] = { + 0x11, 0x00, /* ver, type, code */ + 0xde, 0xad, /* session id */ + 0x00, 0x00, /* length, set below */ + 0x00, 0x00, /* PPP protocol, set below */ + }; + struct ethhdr eth; + /* + * The PPPoE length field covers everything after the 6 byte + * session header: the PPP protocol field plus the payload. + */ + __u16 plen = skb->len - ETH_HLEN_TEST + 2; + + hdr[4] = (plen >> 8) & 0xff; + hdr[5] = plen & 0xff; + + switch (skb->protocol) { + case bpf_htons(ETH_P_IP_TEST): + hdr[7] = PPP_IP_TEST; + break; + case bpf_htons(ETH_P_IPV6_TEST): + hdr[7] = PPP_IPV6_TEST; + break; + default: + return TC_ACT_SHOT_TEST; + } + + if (bpf_skb_adjust_room(skb, PPPOE_SES_HLEN_TEST, BPF_ADJ_ROOM_MAC, + BPF_F_ADJ_ROOM_ENCAP_PPPOE)) + return TC_ACT_SHOT_TEST; + + encap_proto = skb->protocol; + + if (bpf_skb_store_bytes(skb, ETH_HLEN_TEST, hdr, sizeof(hdr), 0)) + return TC_ACT_SHOT_TEST; + + if (bpf_skb_load_bytes(skb, 0, ð, sizeof(eth))) + return TC_ACT_SHOT_TEST; + eth.h_proto = bpf_htons(ETH_P_PPP_SES_TEST); + if (bpf_skb_store_bytes(skb, 0, ð, sizeof(eth), 0)) + return TC_ACT_SHOT_TEST; + + return TC_ACT_OK_TEST; +} + +SEC("tc") +int tc_pppoe_decap(struct __sk_buff *skb) +{ + struct ethhdr eth; + + if (bpf_skb_load_bytes(skb, 0, ð, sizeof(eth))) + return TC_ACT_SHOT_TEST; + if (eth.h_proto != bpf_htons(ETH_P_PPP_SES_TEST)) + return TC_ACT_SHOT_TEST; + + if (bpf_skb_adjust_room(skb, -PPPOE_SES_HLEN_TEST, BPF_ADJ_ROOM_MAC, + BPF_F_ADJ_ROOM_DECAP_PPPOE)) + return TC_ACT_SHOT_TEST; + + decap_proto = skb->protocol; + + /* + * Restore the ethertype to the protocol of the decapsulated + * payload, as picked by the kernel from the PPP protocol field. + */ + eth.h_proto = (__be16)skb->protocol; + if (bpf_skb_store_bytes(skb, 0, ð, sizeof(eth), 0)) + return TC_ACT_SHOT_TEST; + + return TC_ACT_OK_TEST; +} + +/* + * Every bpf_skb_adjust_room() call below must be rejected by the + * helper; tc_pppoe_reject reports (and fails the test) if one of + * them unexpectedly succeeds. + */ +SEC("tc") +int tc_pppoe_reject(struct __sk_buff *skb) +{ + int ret = 0; + + switch (reject_case) { + case 1: + /* Encap with a wrong room size. */ + ret = bpf_skb_adjust_room(skb, PPPOE_SES_HLEN_TEST - 4, + BPF_ADJ_ROOM_MAC, + BPF_F_ADJ_ROOM_ENCAP_PPPOE); + break; + case 2: + /* Encap at the wrong position. */ + ret = bpf_skb_adjust_room(skb, PPPOE_SES_HLEN_TEST, + BPF_ADJ_ROOM_NET, + BPF_F_ADJ_ROOM_ENCAP_PPPOE); + break; + case 3: + /* Encap with a negative room size. */ + ret = bpf_skb_adjust_room(skb, -PPPOE_SES_HLEN_TEST, + BPF_ADJ_ROOM_MAC, + BPF_F_ADJ_ROOM_ENCAP_PPPOE); + break; + case 4: + /* Encap flag combined with a decap flag. */ + ret = bpf_skb_adjust_room(skb, PPPOE_SES_HLEN_TEST, + BPF_ADJ_ROOM_MAC, + BPF_F_ADJ_ROOM_ENCAP_PPPOE | + BPF_F_ADJ_ROOM_DECAP_PPPOE); + break; + case 5: + /* Shrink of a PPPoE packet without the PPPoE flag. */ + ret = bpf_skb_adjust_room(skb, -PPPOE_SES_HLEN_TEST, + BPF_ADJ_ROOM_MAC, 0); + break; + case 6: + /* Decap of a non-PPPoE packet (plain IP or fake PPP proto). */ + ret = bpf_skb_adjust_room(skb, -PPPOE_SES_HLEN_TEST, + BPF_ADJ_ROOM_MAC, + BPF_F_ADJ_ROOM_DECAP_PPPOE); + break; + } + + if (!ret) + reject_unexpected = 1; + + return TC_ACT_SHOT_TEST; +} + +char _license[] SEC("license") = "GPL";
--
2.47.3