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Wed, 22 Jul 2026 03:45:03 -0700 (PDT) From: Mahe Tardy To: bpf@vger.kernel.org Cc: andrew+netdev@lunn.ch, andrii@kernel.org, ast@kernel.org, daniel@iogearbox.net, davem@davemloft.net, eddyz87@gmail.com, edumazet@google.com, john.fastabend@gmail.com, kuba@kernel.org, liamwisehart@meta.com, martin.lau@linux.dev, pabeni@redhat.com, song@kernel.org, netdev@vger.kernel.org, sdf.kernel@gmail.com, ameryhung@gmail.com, kuniyu@google.com, Mahe Tardy Subject: [PATCH bpf-next v2 4/5] selftests/bpf: Add ksock LSM recursion test Date: Wed, 22 Jul 2026 10:44:53 +0000 Message-Id: <20260722104454.165911-5-mahe.tardy@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260722104454.165911-1-mahe.tardy@gmail.com> References: <20260722104454.165911-1-mahe.tardy@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 The bpf_ksock_send() kfunc triggers the security_socket_sendmsg() LSM hook via kernel_sendmsg(), thus attaching an LSM program triggering that kfunc on the same hook would provoke recursion. This test exercises that path and make sure that recursion is guarded and prevented. Signed-off-by: Mahe Tardy --- .../testing/selftests/bpf/prog_tests/ksock.c | 84 +++++++++++++++++-- .../testing/selftests/bpf/progs/ksock_basic.c | 33 +------- .../selftests/bpf/progs/ksock_common.h | 37 ++++++++ .../selftests/bpf/progs/ksock_recursion.c | 69 +++++++++++++++ 4 files changed, 186 insertions(+), 37 deletions(-) create mode 100644 tools/testing/selftests/bpf/progs/ksock_recursion.c diff --git a/tools/testing/selftests/bpf/prog_tests/ksock.c b/tools/testing/selftests/bpf/prog_tests/ksock.c index 5b22ece4be4e..f66660fc191d 100644 --- a/tools/testing/selftests/bpf/prog_tests/ksock.c +++ b/tools/testing/selftests/bpf/prog_tests/ksock.c @@ -6,8 +6,10 @@ #include "test_progs.h" #include "network_helpers.h" #include "ksock_basic.skel.h" +#include "ksock_recursion.skel.h" #define NS_TEST "ksock_basic_ns" +#define NS_LSM_RECURSION_TEST "ksock_lsm_recursion_ns" #define LOOPBACK_IP "127.0.0.1" #define RECV_PORT 7777 #define RECV_TIMEOUT_SEC 5 @@ -98,15 +100,16 @@ static void ksock_assert_recv(struct ksock_test_env *env, const char *data, ASSERT_MEMEQ(env->buf, data, data_sz, "payload match"); } -static bool ksock_setup_ctx(struct ksock_basic *skel) +static bool ksock_setup_ctx(struct bpf_program *prog, __be32 *ipv4_remote, + __u16 *remote_port) { LIBBPF_OPTS(bpf_test_run_opts, opts); int err, pfd; - skel->bss->ipv4_remote = inet_addr(LOOPBACK_IP); - skel->bss->remote_port = RECV_PORT; + *ipv4_remote = inet_addr(LOOPBACK_IP); + *remote_port = RECV_PORT; - pfd = bpf_program__fd(skel->progs.ksock_setup); + pfd = bpf_program__fd(prog); err = bpf_prog_test_run_opts(pfd, &opts); if (!ASSERT_OK(err, "ksock_setup run")) return false; @@ -137,7 +140,9 @@ void test_ksock_basic(void) goto fail; /* Step 1: Run the setup SYSCALL prog to create ksock */ - if (!ksock_setup_ctx(skel)) + if (!ksock_setup_ctx(skel->progs.ksock_setup, + &skel->bss->ipv4_remote, + &skel->bss->remote_port)) goto fail; /* Step 2: Run the send SYSCALL prog */ @@ -157,3 +162,72 @@ void test_ksock_basic(void) ksock_test_env_cleanup(&env); ksock_basic__destroy(skel); } + +void test_ksock_lsm_recursion(void) +{ + struct ksock_test_env env; + struct ksock_recursion *skel; + char trigger = 'x'; + int tfd = -1; + int err; + ssize_t n; + + skel = ksock_recursion__open(); + if (!ASSERT_OK_PTR(skel, "skel open")) + return; + + err = ksock_recursion__load(skel); + if (!ASSERT_OK(err, "skel load")) { + ksock_recursion__destroy(skel); + return; + } + + if (!ksock_test_env_setup(&env, NS_LSM_RECURSION_TEST)) + goto fail; + + /* Step 1: Run the setup SYSCALL prog to create the ksock */ + if (!ksock_setup_ctx(skel->progs.ksock_setup, + &skel->bss->ipv4_remote, + &skel->bss->remote_port)) + goto fail; + + /* Step 2: Attach LSM prog and trigger socket_sendmsg from userspace */ + skel->links.ksock_socket_sendmsg = + bpf_program__attach_lsm(skel->progs.ksock_socket_sendmsg); + if (!ASSERT_OK_PTR(skel->links.ksock_socket_sendmsg, + "attach socket_sendmsg lsm")) + goto fail; + + tfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); + if (!ASSERT_OK_FD(tfd, "trigger socket")) + goto fail; + + skel->bss->target_pid = getpid(); + skel->bss->trigger_send = 1; + n = sendto(tfd, &trigger, sizeof(trigger), 0, + (struct sockaddr *)&env.addr, sizeof(env.addr)); + skel->bss->target_pid = 0; + skel->bss->trigger_send = 0; + if (!ASSERT_EQ(n, sizeof(trigger), "trigger sendto")) + goto fail; + + /* Step 3: The nested bpf_ksock_send() must hit the recursion guard */ + if (!ASSERT_EQ(skel->bss->rec_count, 2, + "socket_sendmsg recursion count")) + goto fail; + if (!ASSERT_EQ(skel->data->rec_kfunc_rets[0], -EBUSY, + "recursive send status")) + goto fail; + if (!ASSERT_EQ(skel->data->rec_kfunc_rets[1], + sizeof(skel->data->send_data), "outer send bytes")) + goto fail; + + ksock_assert_recv(&env, skel->data->send_data, + sizeof(skel->data->send_data)); + +fail: + if (tfd >= 0) + close(tfd); + ksock_test_env_cleanup(&env); + ksock_recursion__destroy(skel); +} diff --git a/tools/testing/selftests/bpf/progs/ksock_basic.c b/tools/testing/selftests/bpf/progs/ksock_basic.c index e8131932d97b..189b0fc15770 100644 --- a/tools/testing/selftests/bpf/progs/ksock_basic.c +++ b/tools/testing/selftests/bpf/progs/ksock_basic.c @@ -8,41 +8,10 @@ #include "bpf_tracing_net.h" #include "ksock_common.h" -__be32 ipv4_remote; -__u16 remote_port; - -char send_data[32] = "hello from bpf ksock"; - SEC("syscall") int ksock_setup(void *ctx) { - struct bpf_ksock_create_opts create_opts = {}; - struct bpf_ksock_addr_opts addr_opts = {}; - struct bpf_ksock *ks; - int err = 0; - - create_opts.family = AF_INET; - create_opts.type = SOCK_DGRAM; - create_opts.protocol = IPPROTO_UDP; - - ks = bpf_ksock_create(&create_opts, sizeof(create_opts), &err); - if (!ks) - return err; - - addr_opts.family = AF_INET; - addr_opts.port = remote_port; - addr_opts.ipv4_addr = ipv4_remote; - - err = bpf_ksock_connect(ks, &addr_opts, sizeof(addr_opts)); - if (err) { - bpf_ksock_release(ks); - return err; - } - - err = ksock_ctx_insert(ks); - if (err && err != -EEXIST) - return err; - return 0; + return do_ksock_setup(); } SEC("syscall") diff --git a/tools/testing/selftests/bpf/progs/ksock_common.h b/tools/testing/selftests/bpf/progs/ksock_common.h index 77f30a42be60..dc3eed78fb2f 100644 --- a/tools/testing/selftests/bpf/progs/ksock_common.h +++ b/tools/testing/selftests/bpf/progs/ksock_common.h @@ -59,4 +59,41 @@ static inline int ksock_ctx_insert(struct bpf_ksock *ctx) return 0; } +/* Globals for passing config from userspace */ +__be32 ipv4_remote; +__u16 remote_port; + +char send_data[32] = "hello from bpf ksock"; + +static inline int do_ksock_setup(void) +{ + struct bpf_ksock_create_opts create_opts = {}; + struct bpf_ksock_addr_opts addr_opts = {}; + struct bpf_ksock *ks; + int err = 0; + + create_opts.family = AF_INET; + create_opts.type = SOCK_DGRAM; + create_opts.protocol = IPPROTO_UDP; + + ks = bpf_ksock_create(&create_opts, sizeof(create_opts), &err); + if (!ks) + return err; + + addr_opts.family = AF_INET; + addr_opts.port = remote_port; + addr_opts.ipv4_addr = ipv4_remote; + + err = bpf_ksock_connect(ks, &addr_opts, sizeof(addr_opts)); + if (err) { + bpf_ksock_release(ks); + return err; + } + + err = ksock_ctx_insert(ks); + if (err && err != -EEXIST) + return err; + return 0; +} + #endif /* _KSOCK_COMMON_H */ diff --git a/tools/testing/selftests/bpf/progs/ksock_recursion.c b/tools/testing/selftests/bpf/progs/ksock_recursion.c new file mode 100644 index 000000000000..52f5200943e3 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/ksock_recursion.c @@ -0,0 +1,69 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 Isovalent */ + +#include "vmlinux.h" +#include +#include +#include +#include "bpf_tracing_net.h" +#include "ksock_common.h" + +void bpf_rcu_read_lock(void) __ksym; +void bpf_rcu_read_unlock(void) __ksym; + +int target_pid; +int trigger_send; + +unsigned int rec_count; +int rec_kfunc_rets[] = { -1, -1 }; + +SEC("syscall") +int ksock_setup(void *ctx) +{ + return do_ksock_setup(); +} + +SEC("lsm.s/socket_sendmsg") +int BPF_PROG(ksock_socket_sendmsg, struct socket *sock, struct msghdr *msg, + int size, int ret) +{ + struct __ksock_ctx_value *v; + struct bpf_ksock *ks, *tmp; + u32 pid = bpf_get_current_pid_tgid() >> 32; + int kfunc_ret; + + if (ret || !trigger_send || pid != target_pid) + return ret; + + v = ksock_ctx_value_lookup(); + if (!v) { + kfunc_ret = -ENOENT; + goto out; + } + + ks = NULL; + bpf_rcu_read_lock(); + tmp = v->ctx; + if (tmp) + ks = bpf_ksock_acquire(tmp); + bpf_rcu_read_unlock(); + + if (!ks) { + kfunc_ret = -ENOENT; + goto out; + } + + kfunc_ret = bpf_ksock_send(ks, send_data, sizeof(send_data)); + bpf_ksock_release(ks); + +out: + rec_kfunc_rets[rec_count & 1] = kfunc_ret; + __sync_fetch_and_add(&rec_count, 1); + + if (kfunc_ret != -EBUSY) + trigger_send = 0; + + return ret; +} + +char __license[] SEC("license") = "GPL"; -- 2.34.1