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Sun, 30 Aug 2026 19:39:39 -0700 (PDT) From: Sanghyun Park To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , bpf@vger.kernel.org Cc: Sanghyun Park , Leon Hwang , John Fastabend , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , Shuah Khan , Stanislav Fomichev , Pu Lehui , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH bpf-next v4 2/2] selftests/bpf: Cover attach type checks in link update Date: Mon, 31 Aug 2026 11:39:12 +0900 Message-ID: <20260831023918.1857658-2-sanghyun.park.cnu@gmail.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20260831023918.1857658-1-sanghyun.park.cnu@gmail.com> References: <20260831023918.1857658-1-sanghyun.park.cnu@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add regression coverage for link update compatibility. Verify that a UDP6 sock_addr program cannot replace a UDP4 program and that an LSM_MAC program cannot replace an LSM_CGROUP program. Also verify that CGROUP_SKB attachment still requires CAP_NET_ADMIN, while an existing link can be updated after dropping CAP_NET_ADMIN and CAP_SYS_ADMIN. Signed-off-by: Sanghyun Park --- .../selftests/bpf/prog_tests/cgroup_link.c | 51 +++++++++++++++++++ .../selftests/bpf/prog_tests/lsm_cgroup.c | 10 ++++ .../testing/selftests/bpf/progs/lsm_cgroup.c | 6 +++ .../selftests/bpf/progs/test_cgroup_link.c | 14 ++++- 4 files changed, 80 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_link.c b/tools/testing/selftests/bpf/prog_tests/cgroup_link.c index 15093a69510e..b3219314596e 100644 --- a/tools/testing/selftests/bpf/prog_tests/cgroup_link.c +++ b/tools/testing/selftests/bpf/prog_tests/cgroup_link.c @@ -1,6 +1,7 @@ // SPDX-License-Identifier: GPL-2.0 #include +#include "cap_helpers.h" #include "cgroup_helpers.h" #include "testing_helpers.h" #include "test_cgroup_link.skel.h" @@ -24,6 +25,55 @@ int ping_and_check(int exp_calls, int exp_alt_calls) return 0; } +static void test_cgroup_link_update(int cg_fd) +{ + const __u64 caps = (1ULL << CAP_NET_ADMIN) | (1ULL << CAP_SYS_ADMIN); + struct bpf_link *link = NULL; + __u64 saved_caps = 0; + int err; + + link = bpf_program__attach_cgroup(skel->progs.sendmsg4, cg_fd); + if (!ASSERT_OK_PTR(link, "attach_sendmsg4")) + goto cleanup; + + err = bpf_link__update_program(link, skel->progs.sendmsg6); + ASSERT_EQ(err, -EINVAL, "reject_sendmsg6_update"); + bpf_link__destroy(link); + link = NULL; + + err = cap_disable_effective(caps, &saved_caps); + if (!ASSERT_OK(err, "drop_caps_for_attach")) + goto cleanup; + + link = bpf_program__attach_cgroup(skel->progs.egress, cg_fd); + if (!ASSERT_ERR_PTR(link, "attach_without_net_admin")) + goto cleanup; + err = libbpf_get_error(link); + link = NULL; + if (!ASSERT_EQ(err, -EPERM, "attach_err")) + goto cleanup; + + err = cap_enable_effective(saved_caps & caps, NULL); + if (!ASSERT_OK(err, "restore_caps_for_attach")) + goto cleanup; + + link = bpf_program__attach_cgroup(skel->progs.egress, cg_fd); + if (!ASSERT_OK_PTR(link, "attach_egress")) + goto cleanup; + + err = cap_disable_effective(caps, &saved_caps); + if (!ASSERT_OK(err, "drop_caps")) + goto cleanup; + + err = bpf_link__update_program(link, skel->progs.egress_alt); + ASSERT_OK(err, "update_without_net_admin"); + +cleanup: + err = cap_enable_effective(saved_caps & caps, NULL); + ASSERT_OK(err, "restore_caps"); + bpf_link__destroy(link); +} + void serial_test_cgroup_link(void) { struct { @@ -61,6 +111,7 @@ void serial_test_cgroup_link(void) err = join_cgroup(cgs[last_cg].path); if (CHECK(err, "cg_join", "fail: %d\n", err)) goto cleanup; + test_cgroup_link_update(cgs[last_cg].fd); for (i = 0; i < cg_nr; i++) { links[i] = bpf_program__attach_cgroup(skel->progs.egress, diff --git a/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c b/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c index 41e867467f6c..85b0af4f486a 100644 --- a/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c +++ b/tools/testing/selftests/bpf/prog_tests/lsm_cgroup.c @@ -74,6 +74,7 @@ static void test_lsm_cgroup_functional(void) int bind_prog_fd = -1; int bind_link_fd = -1; int clone_prog_fd = -1; + int mac_prog_fd; int err, fd, prio; socklen_t socklen; @@ -156,6 +157,15 @@ static void test_lsm_cgroup_functional(void) ASSERT_EQ(query_prog_cnt(cgroup_fd, "bpf_lsm_socket_bind"), 1, "prog count"); ASSERT_EQ(query_prog_cnt(cgroup_fd, NULL), 4, "total prog count"); + fd = bpf_link_create(bpf_program__fd(skel->progs.socket_first), + cgroup_fd, BPF_LSM_CGROUP, NULL); + if (!ASSERT_GE(fd, 0, "link create socket_first")) + goto detach_cgroup; + mac_prog_fd = bpf_program__fd(skel->progs.socket_create_lsm); + err = bpf_link_update(fd, mac_prog_fd, NULL); + ASSERT_EQ(err, -EINVAL, "reject lsm_mac link update"); + close(fd); + /* Attach another instance of bind program to another cgroup. * This should trigger the reuse of the trampoline shim (two * programs attaching to the same btf_id). diff --git a/tools/testing/selftests/bpf/progs/lsm_cgroup.c b/tools/testing/selftests/bpf/progs/lsm_cgroup.c index 3bfa479104be..30727945cecc 100644 --- a/tools/testing/selftests/bpf/progs/lsm_cgroup.c +++ b/tools/testing/selftests/bpf/progs/lsm_cgroup.c @@ -213,6 +213,12 @@ int BPF_PROG(socket_first, int family, int type, int protocol, int kern) return 0; } +SEC("lsm/socket_create") +int BPF_PROG(socket_create_lsm, int family, int type, int protocol, int kern) +{ + return 0; +} + SEC("lsm_cgroup/socket_create") int BPF_PROG(socket_second, int family, int type, int protocol, int kern) { diff --git a/tools/testing/selftests/bpf/progs/test_cgroup_link.c b/tools/testing/selftests/bpf/progs/test_cgroup_link.c index 4faba88e45a5..a987744d129c 100644 --- a/tools/testing/selftests/bpf/progs/test_cgroup_link.c +++ b/tools/testing/selftests/bpf/progs/test_cgroup_link.c @@ -20,5 +20,17 @@ int egress_alt(struct __sk_buff *skb) return 1; } -char _license[] SEC("license") = "GPL"; +SEC("cgroup/sendmsg4") +int sendmsg4(struct bpf_sock_addr *ctx) +{ + return 1; +} +SEC("cgroup/sendmsg6") +int sendmsg6(struct bpf_sock_addr *ctx) +{ + ctx->msg_src_ip6[2] = 0; + return 1; +} + +char _license[] SEC("license") = "GPL"; -- 2.48.1