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[2003:cf:5749:de00:7c66:abd9:5f8b:deba]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-64750a6ea36sm12307884a12.2.2025.12.01.04.24.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Dec 2025 04:24:27 -0800 (PST) From: Alexander Mikhalitsyn To: kees@kernel.org Cc: linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, bpf@vger.kernel.org, Andy Lutomirski , Will Drewry , Jonathan Corbet , Shuah Khan , Tycho Andersen , Andrei Vagin , Christian Brauner , =?UTF-8?q?St=C3=A9phane=20Graber?= , Alexander Mikhalitsyn Subject: [PATCH v1 6/6] tools/testing/selftests/seccomp: test nested listeners Date: Mon, 1 Dec 2025 13:24:03 +0100 Message-ID: <20251201122406.105045-7-aleksandr.mikhalitsyn@canonical.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251201122406.105045-1-aleksandr.mikhalitsyn@canonical.com> References: <20251201122406.105045-1-aleksandr.mikhalitsyn@canonical.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Add some basic tests for nested listeners. Cc: linux-kernel@vger.kernel.org Cc: linux-kselftest@vger.kernel.org Cc: bpf@vger.kernel.org Cc: Kees Cook Cc: Andy Lutomirski Cc: Will Drewry Cc: Jonathan Corbet Cc: Shuah Khan Cc: Tycho Andersen Cc: Andrei Vagin Cc: Christian Brauner Cc: St=C3=A9phane Graber Signed-off-by: Alexander Mikhalitsyn --- tools/testing/selftests/seccomp/seccomp_bpf.c | 162 ++++++++++++++++++ 1 file changed, 162 insertions(+) diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/= selftests/seccomp/seccomp_bpf.c index fc4910d35342..0bf02d04fe15 100644 --- a/tools/testing/selftests/seccomp/seccomp_bpf.c +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c @@ -293,6 +293,10 @@ struct seccomp_notif_addfd_big { #define SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV (1UL << 5) #endif =20 +#ifndef SECCOMP_FILTER_FLAG_ALLOW_NESTED_LISTENERS +#define SECCOMP_FILTER_FLAG_ALLOW_NESTED_LISTENERS (1UL << 6) +#endif + #ifndef seccomp int seccomp(unsigned int op, unsigned int flags, void *args) { @@ -4408,6 +4412,164 @@ TEST(user_notification_sync) ASSERT_EQ(status, 0); } =20 +/* from kernel/seccomp.c */ +#define MAX_LISTENERS_PER_PATH 8 + +TEST(user_notification_nested_limits) +{ + pid_t pid; + long ret; + int i, status, listeners[MAX_LISTENERS_PER_PATH]; + + struct sock_filter filter[] =3D { + BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW), + }; + struct sock_fprog prog =3D { + .len =3D (unsigned short)ARRAY_SIZE(filter), + .filter =3D filter, + }; + + ret =3D prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0); + ASSERT_EQ(0, ret) { + TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!"); + } + + /* Install 6 levels of listeners and allow nesting. */ + for (i =3D 0; i < 6; i++) { + listeners[i] =3D user_notif_syscall(__NR_getppid, + SECCOMP_FILTER_FLAG_NEW_LISTENER | + SECCOMP_FILTER_FLAG_ALLOW_NESTED_LISTENERS); + ASSERT_GE(listeners[i], 0); + + /* Add some no-op filters for grins. */ + EXPECT_EQ(seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog), 0); + } + + /* Check behavior when nesting is not allowed. */ + pid =3D fork(); + ASSERT_GE(pid, 0); + if (pid =3D=3D 0) { + /* Install a next listener in the chain without nesting allowed. */ + listeners[6] =3D user_notif_syscall(__NR_getppid, + SECCOMP_FILTER_FLAG_NEW_LISTENER); + if (listeners[6] < 0) + exit(1); + + /* Add some no-op filters for grins. */ + ret =3D seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog); + if (ret !=3D 0) + exit(2); + + ret =3D user_notif_syscall(__NR_getppid, + SECCOMP_FILTER_FLAG_NEW_LISTENER); + /* Installing a next listener in the chain should result in EBUSY. */ + exit((ret >=3D 0 || errno !=3D EBUSY) ? 3 : 0); + } + + EXPECT_EQ(waitpid(pid, &status, 0), pid); + EXPECT_EQ(true, WIFEXITED(status)); + EXPECT_EQ(0, WEXITSTATUS(status)); + + /* Install more filters with listeners to reach nesting levels limit. */ + for (; i < MAX_LISTENERS_PER_PATH; i++) { + listeners[i] =3D user_notif_syscall(__NR_getppid, + SECCOMP_FILTER_FLAG_NEW_LISTENER | + SECCOMP_FILTER_FLAG_ALLOW_NESTED_LISTENERS); + ASSERT_GE(listeners[i], 0); + + /* Add some no-op filters for grins. */ + EXPECT_EQ(seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog), 0); + } + + /* Installing a next listener in the chain should result in ELOOP. */ + EXPECT_EQ(user_notif_syscall(__NR_getppid, + SECCOMP_FILTER_FLAG_NEW_LISTENER), + -1); + EXPECT_EQ(errno, ELOOP); +} + +TEST(user_notification_nested) +{ + pid_t pid; + long ret; + int i, status, listeners[6]; + struct seccomp_notif req =3D {}; + struct seccomp_notif_resp resp =3D {}; + + struct sock_filter filter[] =3D { + BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW), + }; + struct sock_fprog prog =3D { + .len =3D (unsigned short)ARRAY_SIZE(filter), + .filter =3D filter, + }; + + ret =3D prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0); + ASSERT_EQ(0, ret) { + TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!"); + } + + /* Install 6 levels of listeners and allow nesting. */ + for (i =3D 0; i < 6; i++) { + listeners[i] =3D user_notif_syscall(__NR_getppid, + SECCOMP_FILTER_FLAG_NEW_LISTENER | + SECCOMP_FILTER_FLAG_ALLOW_NESTED_LISTENERS); + ASSERT_GE(listeners[i], 0); + + /* Add some no-op filters for grins. */ + EXPECT_EQ(seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog), 0); + } + + pid =3D fork(); + ASSERT_GE(pid, 0); + + if (pid =3D=3D 0) { + ret =3D syscall(__NR_getppid); + exit(ret !=3D (USER_NOTIF_MAGIC-3)); + } + + /* + * We want to have the following picture: + * + * | Listener level (i) | Listener decision | + * |--------------------|-------------------| + * | 0 | WHATEVER | + * | 1 | WHATEVER | + * | 2 | WHATEVER | + * | 3 | RETURN | <-- stop here + * | 4 | CONTINUE SYSCALL | + * | 5 | CONTINUE SYSCALL | <- start here (current->seccomp.filter) + * + * First listener who receives a notification is level 5, then 4, + * then we expect to stop on level 3 and return from syscall with + * (USER_NOTIF_MAGIC - 3) return value. + */ + for (i =3D 6 - 1; i >=3D 3; i--) { + memset(&req, 0, sizeof(req)); + EXPECT_EQ(ioctl(listeners[i], SECCOMP_IOCTL_NOTIF_RECV, &req), 0); + EXPECT_EQ(req.pid, pid); + EXPECT_EQ(req.data.nr, __NR_getppid); + + memset(&resp, 0, sizeof(resp)); + resp.id =3D req.id; + + if (i =3D=3D 5 || i =3D=3D 4) { + resp.flags =3D SECCOMP_USER_NOTIF_FLAG_CONTINUE; + } else { + resp.error =3D 0; + resp.val =3D USER_NOTIF_MAGIC - i; + } + + EXPECT_EQ(ioctl(listeners[i], SECCOMP_IOCTL_NOTIF_SEND, &resp), 0); + } + + EXPECT_EQ(waitpid(pid, &status, 0), pid); + EXPECT_EQ(true, WIFEXITED(status)); + EXPECT_EQ(0, WEXITSTATUS(status)); + + for (i =3D 0; i < 6; i++) + close(listeners[i]); +} =20 /* Make sure PTRACE_O_SUSPEND_SECCOMP requires CAP_SYS_ADMIN. */ FIXTURE(O_SUSPEND_SECCOMP) { --=20 2.43.0