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[2003:cf:5702:2000:e621:9d57:9862:e30]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47a89f0d6f2sm32075905e9.13.2025.12.11.04.46.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Dec 2025 04:46:42 -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 , Aleksa Sarai , Tycho Andersen , Andrei Vagin , Christian Brauner , =?UTF-8?q?St=C3=A9phane=20Graber?= , Alexander Mikhalitsyn Subject: [PATCH v3 7/7] tools/testing/selftests/seccomp: test nested listeners Date: Thu, 11 Dec 2025 13:46:11 +0100 Message-ID: <20251211124614.161900-8-aleksandr.mikhalitsyn@canonical.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251211124614.161900-1-aleksandr.mikhalitsyn@canonical.com> References: <20251211124614.161900-1-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: Aleksa Sarai 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 | 303 ++++++++++++++++++ 1 file changed, 303 insertions(+) diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/= selftests/seccomp/seccomp_bpf.c index 874f17763536..bbf3ef58ad07 100644 --- a/tools/testing/selftests/seccomp/seccomp_bpf.c +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c @@ -301,6 +301,10 @@ 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) { @@ -4416,6 +4420,305 @@ TEST(user_notification_sync) ASSERT_EQ(status, 0); } =20 +/* + * This test is here to ensure that seccomp() behavior before + * introducing nested listeners is preserved. + */ +TEST(user_notification_many_ret_notif_old_behavior) +{ + pid_t pid, ppid; + long ret; + int status, listener; + 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!"); + } + + /* Add some no-op filters for grins. */ + EXPECT_EQ(seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog), 0); + + /* Install a filter that returns SECCOMP_RET_USER_NOTIF, but has no liste= ner. */ + ASSERT_GE(user_notif_syscall(__NR_getppid, 0), 0); + + /* Install a filter that returns SECCOMP_RET_USER_NOTIF, and then close l= istener. */ + listener =3D user_notif_syscall(__NR_getppid, + SECCOMP_FILTER_FLAG_NEW_LISTENER); + ASSERT_GE(listener, 0); + close(listener); + + /* + * Note, that we can install another listener now (without nesting enable= d!), + * because notify fd of the previous filter has been closed. + */ + listener =3D user_notif_syscall(__NR_getppid, + SECCOMP_FILTER_FLAG_NEW_LISTENER); + ASSERT_GE(listener, 0); + + /* Add some no-op filters for grins. */ + EXPECT_EQ(seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog), 0); + + ppid =3D getpid(); + pid =3D fork(); + ASSERT_GE(pid, 0); + + if (pid =3D=3D 0) { + ret =3D syscall(__NR_getppid); + exit(ret !=3D ppid); + } + + memset(&req, 0, sizeof(req)); + EXPECT_EQ(ioctl(listener, 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; + + /* tell kernel to continue syscall and expect that upper-level filters ar= e ignored */ + resp.flags =3D SECCOMP_USER_NOTIF_FLAG_CONTINUE; + + EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), 0); + + EXPECT_EQ(waitpid(pid, &status, 0), pid); + EXPECT_EQ(true, WIFEXITED(status)); + EXPECT_EQ(0, WEXITSTATUS(status)); + + close(listener); +} + +TEST(user_notification_many_ret_notif_closed_listener_nested) +{ + pid_t pid; + long ret; + int status, listener, closed_listener; + 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!"); + } + + /* Add some no-op filters for grins. */ + EXPECT_EQ(seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog), 0); + + closed_listener =3D user_notif_syscall(__NR_getppid, + SECCOMP_FILTER_FLAG_NEW_LISTENER | + SECCOMP_FILTER_FLAG_ALLOW_NESTED_LISTENERS); + ASSERT_GE(closed_listener, 0); + + /* + * Note, that we can install another listener now (without nesting enable= d!), + * because notify fd of the previous filter has been closed. + */ + listener =3D user_notif_syscall(__NR_getppid, + SECCOMP_FILTER_FLAG_NEW_LISTENER); + ASSERT_GE(listener, 0); + + /* Now, once we installed a nested listener, close the previous one. */ + close(closed_listener); + + /* 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 0 || errno !=3D ENOSYS); + } + + memset(&req, 0, sizeof(req)); + EXPECT_EQ(ioctl(listener, 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; + + /* + * Tell kernel to continue syscall and expect ENOSYS, + * because upper filter's notify fd has been closed. + */ + resp.flags =3D SECCOMP_USER_NOTIF_FLAG_CONTINUE; + + EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), 0); + + EXPECT_EQ(waitpid(pid, &status, 0), pid); + EXPECT_EQ(true, WIFEXITED(status)); + EXPECT_EQ(0, WEXITSTATUS(status)); + + close(listener); +} + +/* + * Ensure that EBUSY is returned on attempt to + * install a nested listener without nesting being allowed. + */ +TEST(user_notification_nested_limits) +{ + pid_t pid; + long ret; + int i, status, listeners[8]; + + 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)); +} + +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++) { + /* + * Install a filter that returns SECCOMP_RET_USER_NOTIF, but has no list= ener. + * We expect that these filters are not affecting the end result. + */ + ASSERT_GE(user_notif_syscall(__NR_getppid, 0), 0); + + 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