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[95.24.167.79]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-3a9a1d59661sm9000041fa.18.2026.10.07.11.13.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Oct 2026 11:13:18 -0700 (PDT) From: Maxim Skokov To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, memxor@gmail.com, emil@etsalapatis.com, ihor.solodrai@linux.dev, davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, shuah@kernel.org, vadim.fedorenko@linux.dev, netdev@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Maxim Skokov Subject: [PATCH bpf 2/2] selftests/bpf: Cover test_run csum validation after bpf_skb_change_tail() Date: Wed, 7 Oct 2026 21:12:42 +0300 Message-ID: <20261007181249.352831-3-skokovmaksimevg@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261007181249.352831-1-skokovmaksimevg@gmail.com> References: <20261007181249.352831-1-skokovmaksimevg@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add BPF_F_TEST_SKB_CHECKSUM_COMPLETE tests for tc programs that move the skb out of CHECKSUM_COMPLETE with bpf_skb_change_tail(): - change_tail_trim trims the last 4 bytes of pkt_v4. They hold the non-zero tcp.urg_ptr, so the stale skb->csum no longer matches the packet. - change_tail_grow_write appends 4 zero bytes, which on their own do not change the sum, and then writes a byte with BPF_F_RECOMPUTE_CSUM. That write can no longer update skb->csum. Both return -EBADMSG without the preceding test_run fix and pass with it. Also add store_no_recompute as a negative test. It writes a byte without BPF_F_RECOMPUTE_CSUM, so the skb stays CHECKSUM_COMPLETE with a stale skb->csum, and test_run must keep returning -EBADMSG. This checks that the validation still runs for CHECKSUM_COMPLETE skbs. The passing case, a CHECKSUM_COMPLETE skb whose checksum is updated correctly, is already covered by test_skb_pkt_end. Assisted-by: LLM Signed-off-by: Maxim Skokov --- .../bpf/prog_tests/skb_csum_complete.c | 39 ++++++++++++++++ .../selftests/bpf/progs/skb_csum_complete.c | 44 +++++++++++++++++++ 2 files changed, 83 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/skb_csum_complete.c create mode 100644 tools/testing/selftests/bpf/progs/skb_csum_complete.c diff --git a/tools/testing/selftests/bpf/prog_tests/skb_csum_complete.c b/tools/testing/selftests/bpf/prog_tests/skb_csum_complete.c new file mode 100644 index 0000000000000..919f24dbacd3d --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/skb_csum_complete.c @@ -0,0 +1,39 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include "skb_csum_complete.skel.h" + +static void run(struct bpf_program *prog, int expected_err) +{ + LIBBPF_OPTS(bpf_test_run_opts, topts, + .data_in = &pkt_v4, + .data_size_in = sizeof(pkt_v4), + .repeat = 1, + .flags = BPF_F_TEST_SKB_CHECKSUM_COMPLETE, + ); + int err; + + err = bpf_prog_test_run_opts(bpf_program__fd(prog), &topts); + if (!ASSERT_EQ(err, expected_err, "test_run")) + return; + if (!expected_err) + ASSERT_EQ(topts.retval, 0, "retval"); +} + +void test_skb_csum_complete(void) +{ + struct skb_csum_complete *skel; + + skel = skb_csum_complete__open_and_load(); + if (!ASSERT_OK_PTR(skel, "skel_open_and_load")) + return; + + if (test__start_subtest("change_tail_trim")) + run(skel->progs.change_tail_trim, 0); + if (test__start_subtest("change_tail_grow_write")) + run(skel->progs.change_tail_grow_write, 0); + if (test__start_subtest("store_no_recompute")) + run(skel->progs.store_no_recompute, -EBADMSG); + + skb_csum_complete__destroy(skel); +} diff --git a/tools/testing/selftests/bpf/progs/skb_csum_complete.c b/tools/testing/selftests/bpf/progs/skb_csum_complete.c new file mode 100644 index 0000000000000..8e8d53530899a --- /dev/null +++ b/tools/testing/selftests/bpf/progs/skb_csum_complete.c @@ -0,0 +1,44 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include + +SEC("tc") +int change_tail_trim(struct __sk_buff *skb) +{ + /* Drops CHECKSUM_COMPLETE. skb->csum still covers the trimmed bytes, + * which hold the non-zero tcp.urg_ptr of pkt_v4, so it no longer + * matches the packet. + */ + if (bpf_skb_change_tail(skb, skb->len - 4, 0)) + return 1; + return 0; +} + +SEC("tc") +int change_tail_grow_write(struct __sk_buff *skb) +{ + __u8 val = 0xab; + + /* Drops CHECKSUM_COMPLETE. The new bytes are zero and do not change + * the sum, but the write below can no longer update skb->csum. + */ + if (bpf_skb_change_tail(skb, skb->len + 4, 0)) + return 1; + if (bpf_skb_store_bytes(skb, skb->len - 1, &val, sizeof(val), + BPF_F_RECOMPUTE_CSUM)) + return 2; + return 0; +} + +SEC("tc") +int store_no_recompute(struct __sk_buff *skb) +{ + __u8 val = 0xab; + + /* skb stays CHECKSUM_COMPLETE, but skb->csum is not updated. */ + if (bpf_skb_store_bytes(skb, skb->len - 1, &val, sizeof(val), 0)) + return 1; + return 0; +} + +char _license[] SEC("license") = "GPL"; -- 2.47.3