// Copyright 2018 The gVisor Authors. // // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // // http://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. // See the License for the specific language governing permissions and // limitations under the License. #include <errno.h> #include <linux/audit.h> #include <linux/filter.h> #include <linux/seccomp.h> #include <pthread.h> #include <sched.h> #include <signal.h> #include <string.h> #include <sys/prctl.h> #include <sys/syscall.h> #include <time.h> #include <ucontext.h> #include <unistd.h> #include <atomic> #include "gmock/gmock.h" #include "gtest/gtest.h" #include "absl/base/macros.h" #include "test/util/logging.h" #include "test/util/memory_util.h" #include "test/util/multiprocess_util.h" #include "test/util/posix_error.h" #include "test/util/proc_util.h" #include "test/util/test_util.h" #include "test/util/thread_util.h" #ifndef SYS_SECCOMP #define SYS_SECCOMP 1 #endif namespace gvisor { namespace testing { namespace { // A syscall not implemented by Linux that we don't expect to be called. constexpr uint32_t kFilteredSyscall = SYS_vserver; // Applies a seccomp-bpf filter that returns `filtered_result` for // `sysno` and allows all other syscalls. Async-signal-safe. void ApplySeccompFilter(uint32_t sysno, uint32_t filtered_result, uint32_t flags = 0) { // "Prior to [PR_SET_SECCOMP], the task must call prctl(PR_SET_NO_NEW_PRIVS, // 1) or run with CAP_SYS_ADMIN privileges in its namespace." - // Documentation/prctl/seccomp_filter.txt // // prctl(PR_SET_NO_NEW_PRIVS, 1) may be called repeatedly; calls after the // first are no-ops. TEST_PCHECK(prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == 0); MaybeSave(); struct sock_filter filter[] = { // A = seccomp_data.arch BPF_STMT(BPF_LD | BPF_ABS | BPF_W, 4), // if (A != AUDIT_ARCH_X86_64) goto kill BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, AUDIT_ARCH_X86_64, 0, 4), // A = seccomp_data.nr BPF_STMT(BPF_LD | BPF_ABS | BPF_W, 0), // if (A != sysno) goto allow BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, sysno, 0, 1), // return filtered_result BPF_STMT(BPF_RET | BPF_K, filtered_result), // allow: return SECCOMP_RET_ALLOW BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW), // kill: return SECCOMP_RET_KILL BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL), }; struct sock_fprog prog; prog.len = ABSL_ARRAYSIZE(filter); prog.filter = filter; if (flags) { TEST_CHECK(syscall(__NR_seccomp, SECCOMP_SET_MODE_FILTER, flags, &prog) == 0); } else { TEST_PCHECK(prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog, 0, 0) == 0); } MaybeSave(); } // Wrapper for sigaction. Async-signal-safe. void RegisterSignalHandler(int signum, void (*handler)(int, siginfo_t*, void*)) { struct sigaction sa = {}; sa.sa_sigaction = handler; sigemptyset(&sa.sa_mask); sa.sa_flags = SA_SIGINFO; TEST_PCHECK(sigaction(signum, &sa, nullptr) == 0); MaybeSave(); } // All of the following tests execute in a subprocess to ensure that each test // is run in a separate process. This avoids cross-contamination of seccomp // state between tests, and is necessary to ensure that test processes killed // by SECCOMP_RET_KILL are single-threaded (since SECCOMP_RET_KILL only kills // the offending thread, not the whole thread group). TEST(SeccompTest, RetKillCausesDeathBySIGSYS) { pid_t const pid = fork(); if (pid == 0) { // Register a signal handler for SIGSYS that we don't expect to be invoked. RegisterSignalHandler(SIGSYS, +[](int, siginfo_t*, void*) { _exit(1); }); ApplySeccompFilter(kFilteredSyscall, SECCOMP_RET_KILL); syscall(kFilteredSyscall); TEST_CHECK_MSG(false, "Survived invocation of test syscall"); } ASSERT_THAT(pid, SyscallSucceeds()); int status; ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid)); EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGSYS) << "status " << status; } TEST(SeccompTest, RetKillOnlyKillsOneThread) { Mapping stack = ASSERT_NO_ERRNO_AND_VALUE( MmapAnon(2 * kPageSize, PROT_READ | PROT_WRITE, MAP_PRIVATE)); pid_t const pid = fork(); if (pid == 0) { // Register a signal handler for SIGSYS that we don't expect to be invoked. RegisterSignalHandler(SIGSYS, +[](int, siginfo_t*, void*) { _exit(1); }); ApplySeccompFilter(kFilteredSyscall, SECCOMP_RET_KILL); // Pass CLONE_VFORK to block the original thread in the child process until // the clone thread exits with SIGSYS. // // N.B. clone(2) is not officially async-signal-safe, but at minimum glibc's // x86_64 implementation is safe. See glibc // sysdeps/unix/sysv/linux/x86_64/clone.S. clone( +[](void* arg) { syscall(kFilteredSyscall); // should kill the thread _exit(1); // should be unreachable return 2; // should be very unreachable, shut up the compiler }, stack.endptr(), CLONE_FILES | CLONE_FS | CLONE_SIGHAND | CLONE_THREAD | CLONE_VM | CLONE_VFORK, nullptr); _exit(0); } ASSERT_THAT(pid, SyscallSucceeds()); int status; ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid)); EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0) << "status " << status; } TEST(SeccompTest, RetTrapCausesSIGSYS) { pid_t const pid = fork(); if (pid == 0) { constexpr uint16_t kTrapValue = 0xdead; RegisterSignalHandler( SIGSYS, +[](int signo, siginfo_t* info, void* ucv) { ucontext_t* uc = static_cast<ucontext_t*>(ucv); // This is a signal handler, so we must stay async-signal-safe. TEST_CHECK(info->si_signo == SIGSYS); TEST_CHECK(info->si_code == SYS_SECCOMP); TEST_CHECK(info->si_errno == kTrapValue); TEST_CHECK(info->si_call_addr != nullptr); TEST_CHECK(info->si_syscall == kFilteredSyscall); #ifdef __x86_64__ TEST_CHECK(info->si_arch == AUDIT_ARCH_X86_64); TEST_CHECK(uc->uc_mcontext.gregs[REG_RAX] == kFilteredSyscall); #endif // defined(__x86_64__) _exit(0); }); ApplySeccompFilter(kFilteredSyscall, SECCOMP_RET_TRAP | kTrapValue); syscall(kFilteredSyscall); TEST_CHECK_MSG(false, "Survived invocation of test syscall"); } ASSERT_THAT(pid, SyscallSucceeds()); int status; ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid)); EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0) << "status " << status; } #ifdef __x86_64__ constexpr uint64_t kVsyscallTimeEntry = 0xffffffffff600400; time_t vsyscall_time(time_t* t) { return reinterpret_cast<time_t (*)(time_t*)>(kVsyscallTimeEntry)(t); } TEST(SeccompTest, SeccompAppliesToVsyscall) { SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(IsVsyscallEnabled())); pid_t const pid = fork(); if (pid == 0) { constexpr uint16_t kTrapValue = 0xdead; RegisterSignalHandler( SIGSYS, +[](int signo, siginfo_t* info, void* ucv) { ucontext_t* uc = static_cast<ucontext_t*>(ucv); // This is a signal handler, so we must stay async-signal-safe. TEST_CHECK(info->si_signo == SIGSYS); TEST_CHECK(info->si_code == SYS_SECCOMP); TEST_CHECK(info->si_errno == kTrapValue); TEST_CHECK(info->si_call_addr != nullptr); TEST_CHECK(info->si_syscall == SYS_time); TEST_CHECK(info->si_arch == AUDIT_ARCH_X86_64); TEST_CHECK(uc->uc_mcontext.gregs[REG_RAX] == SYS_time); _exit(0); }); ApplySeccompFilter(SYS_time, SECCOMP_RET_TRAP | kTrapValue); vsyscall_time(nullptr); // Should result in death. TEST_CHECK_MSG(false, "Survived invocation of test syscall"); } ASSERT_THAT(pid, SyscallSucceeds()); int status; ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid)); EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0) << "status " << status; } TEST(SeccompTest, RetKillVsyscallCausesDeathBySIGSYS) { SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(IsVsyscallEnabled())); pid_t const pid = fork(); if (pid == 0) { // Register a signal handler for SIGSYS that we don't expect to be invoked. RegisterSignalHandler( SIGSYS, +[](int, siginfo_t*, void*) { _exit(1); }); ApplySeccompFilter(SYS_time, SECCOMP_RET_KILL); vsyscall_time(nullptr); // Should result in death. TEST_CHECK_MSG(false, "Survived invocation of test syscall"); } ASSERT_THAT(pid, SyscallSucceeds()); int status; ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid)); EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGSYS) << "status " << status; } #endif // defined(__x86_64__) TEST(SeccompTest, RetTraceWithoutPtracerReturnsENOSYS) { pid_t const pid = fork(); if (pid == 0) { ApplySeccompFilter(kFilteredSyscall, SECCOMP_RET_TRACE); TEST_CHECK(syscall(kFilteredSyscall) == -1 && errno == ENOSYS); _exit(0); } ASSERT_THAT(pid, SyscallSucceeds()); int status; ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid)); EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0) << "status " << status; } TEST(SeccompTest, RetErrnoReturnsErrno) { pid_t const pid = fork(); if (pid == 0) { // ENOTNAM: "Not a XENIX named type file" ApplySeccompFilter(kFilteredSyscall, SECCOMP_RET_ERRNO | ENOTNAM); TEST_CHECK(syscall(kFilteredSyscall) == -1 && errno == ENOTNAM); _exit(0); } ASSERT_THAT(pid, SyscallSucceeds()); int status; ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid)); EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0) << "status " << status; } TEST(SeccompTest, RetAllowAllowsSyscall) { pid_t const pid = fork(); if (pid == 0) { ApplySeccompFilter(kFilteredSyscall, SECCOMP_RET_ALLOW); TEST_CHECK(syscall(kFilteredSyscall) == -1 && errno == ENOSYS); _exit(0); } ASSERT_THAT(pid, SyscallSucceeds()); int status; ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid)); EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0) << "status " << status; } // This test will validate that TSYNC will apply to all threads. TEST(SeccompTest, TsyncAppliesToAllThreads) { Mapping stack = ASSERT_NO_ERRNO_AND_VALUE( MmapAnon(2 * kPageSize, PROT_READ | PROT_WRITE, MAP_PRIVATE)); // We don't want to apply this policy to other test runner threads, so fork. const pid_t pid = fork(); if (pid == 0) { // First check that we receive a ENOSYS before the policy is applied. TEST_CHECK(syscall(kFilteredSyscall) == -1 && errno == ENOSYS); // N.B. clone(2) is not officially async-signal-safe, but at minimum glibc's // x86_64 implementation is safe. See glibc // sysdeps/unix/sysv/linux/x86_64/clone.S. clone( +[](void* arg) { ApplySeccompFilter(kFilteredSyscall, SECCOMP_RET_ERRNO | ENOTNAM, SECCOMP_FILTER_FLAG_TSYNC); return 0; }, stack.endptr(), CLONE_FILES | CLONE_FS | CLONE_SIGHAND | CLONE_THREAD | CLONE_VM | CLONE_VFORK, nullptr); // Because we're using CLONE_VFORK this thread will be blocked until // the second thread has released resources to our virtual memory, since // we're not execing that will happen on _exit. // Now verify that the policy applied to this thread too. TEST_CHECK(syscall(kFilteredSyscall) == -1 && errno == ENOTNAM); _exit(0); } ASSERT_THAT(pid, SyscallSucceeds()); int status = 0; ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid)); EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0) << "status " << status; } // This test will validate that seccomp(2) rejects unsupported flags. TEST(SeccompTest, SeccompRejectsUnknownFlags) { constexpr uint32_t kInvalidFlag = 123; ASSERT_THAT( syscall(__NR_seccomp, SECCOMP_SET_MODE_FILTER, kInvalidFlag, nullptr), SyscallFailsWithErrno(EINVAL)); } TEST(SeccompTest, LeastPermissiveFilterReturnValueApplies) { // This is RetKillCausesDeathBySIGSYS, plus extra filters before and after the // one that causes the kill that should be ignored. pid_t const pid = fork(); if (pid == 0) { RegisterSignalHandler(SIGSYS, +[](int, siginfo_t*, void*) { _exit(1); }); ApplySeccompFilter(kFilteredSyscall, SECCOMP_RET_TRACE); ApplySeccompFilter(kFilteredSyscall, SECCOMP_RET_KILL); ApplySeccompFilter(kFilteredSyscall, SECCOMP_RET_ERRNO | ENOTNAM); syscall(kFilteredSyscall); TEST_CHECK_MSG(false, "Survived invocation of test syscall"); } ASSERT_THAT(pid, SyscallSucceeds()); int status; ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid)); EXPECT_TRUE(WIFSIGNALED(status) && WTERMSIG(status) == SIGSYS) << "status " << status; } // Passed as argv[1] to cause the test binary to invoke kFilteredSyscall and // exit. Not a real flag since flag parsing happens during initialization, // which may create threads. constexpr char kInvokeFilteredSyscallFlag[] = "--seccomp_test_child"; TEST(SeccompTest, FiltersPreservedAcrossForkAndExecve) { ExecveArray const grandchild_argv( {"/proc/self/exe", kInvokeFilteredSyscallFlag}); pid_t const pid = fork(); if (pid == 0) { ApplySeccompFilter(kFilteredSyscall, SECCOMP_RET_KILL); pid_t const grandchild_pid = fork(); if (grandchild_pid == 0) { execve(grandchild_argv.get()[0], grandchild_argv.get(), /* envp = */ nullptr); TEST_PCHECK_MSG(false, "execve failed"); } int status; TEST_PCHECK(waitpid(grandchild_pid, &status, 0) == grandchild_pid); TEST_CHECK(WIFSIGNALED(status) && WTERMSIG(status) == SIGSYS); _exit(0); } ASSERT_THAT(pid, SyscallSucceeds()); int status; ASSERT_THAT(waitpid(pid, &status, 0), SyscallSucceedsWithValue(pid)); EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0) << "status " << status; } } // namespace } // namespace testing } // namespace gvisor int main(int argc, char** argv) { if (argc >= 2 && strcmp(argv[1], gvisor::testing::kInvokeFilteredSyscallFlag) == 0) { syscall(gvisor::testing::kFilteredSyscall); exit(0); } gvisor::testing::TestInit(&argc, &argv); return RUN_ALL_TESTS(); }