Test that checks performed by execveat(..., AT_CHECK) are consistent with noexec mount points and file execute permissions. Test that SECBIT_SHOULD_EXEC_CHECK and SECBIT_SHOULD_EXEC_RESTRICT are inherited by child processes and that they can be pinned with the appropriate SECBIT_SHOULD_EXEC_CHECK_LOCKED and SECBIT_SHOULD_EXEC_RESTRICT_LOCKED bits. Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Christian Brauner <brauner@xxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Paul Moore <paul@xxxxxxxxxxxxxx> Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx> Link: https://lore.kernel.org/r/20240704190137.696169-4-mic@xxxxxxxxxxx --- Changes since v18: * Rewrite tests with the new design: execveat/AT_CHECK and securebits. * Simplify the capability dropping and improve it with the NOROOT securebits. * Replace most ASSERT with EXPECT. * Fix NULL execve's argv to avoid kernel warning. * Move tests to exec/ * Build a "false" static binary to test full execution path. Changes since v14: * Add Reviewed-by Kees Cook. Changes since v13: * Move -I to CFLAGS (suggested by Kees Cook). * Update sysctl name. Changes since v12: * Fix Makefile's license. Changes since v10: * Update selftest Makefile. Changes since v9: * Rename the syscall and the sysctl. * Update tests for enum trusted_for_usage Changes since v8: * Update with the dedicated syscall introspect_access(2) and the renamed fs.introspection_policy sysctl. * Remove check symlink which can't be use as is anymore. * Use socketpair(2) to test UNIX socket. Changes since v7: * Update tests with faccessat2/AT_INTERPRETED, including new ones to check that setting R_OK or W_OK returns EINVAL. * Add tests for memfd, pipefs and nsfs. * Rename and move back tests to a standalone directory. Changes since v6: * Add full combination tests for all file types, including block devices, character devices, fifos, sockets and symlinks. * Properly save and restore initial sysctl value for all tests. Changes since v5: * Refactor with FIXTURE_VARIANT, which make the tests much more easy to read and maintain. * Save and restore initial sysctl value (suggested by Kees Cook). * Test with a sysctl value of 0. * Check errno in sysctl_access_write test. * Update tests for the CAP_SYS_ADMIN switch. * Update tests to check -EISDIR (replacing -EACCES). * Replace FIXTURE_DATA() with FIXTURE() (spotted by Kees Cook). * Use global const strings. Changes since v3: * Replace RESOLVE_MAYEXEC with O_MAYEXEC. * Add tests to check that O_MAYEXEC is ignored by open(2) and openat(2). Changes since v2: * Move tests from exec/ to openat2/ . * Replace O_MAYEXEC with RESOLVE_MAYEXEC from openat2(2). * Cleanup tests. Changes since v1: * Move tests from yama/ to exec/ . * Fix _GNU_SOURCE in kselftest_harness.h . * Add a new test sysctl_access_write to check if CAP_MAC_ADMIN is taken into account. * Test directory execution which is always forbidden since commit 73601ea5b7b1 ("fs/open.c: allow opening only regular files during execve()"), and also check that even the root user can not bypass file execution checks. * Make sure delete_workspace() always as enough right to succeed. * Cosmetic cleanup. --- tools/testing/selftests/exec/.gitignore | 2 + tools/testing/selftests/exec/Makefile | 8 + tools/testing/selftests/exec/config | 2 + tools/testing/selftests/exec/false.c | 5 + tools/testing/selftests/exec/should-exec.c | 449 +++++++++++++++++++++ 5 files changed, 466 insertions(+) create mode 100644 tools/testing/selftests/exec/config create mode 100644 tools/testing/selftests/exec/false.c create mode 100644 tools/testing/selftests/exec/should-exec.c diff --git a/tools/testing/selftests/exec/.gitignore b/tools/testing/selftests/exec/.gitignore index 90c238ba6a4b..20e965dcc98e 100644 --- a/tools/testing/selftests/exec/.gitignore +++ b/tools/testing/selftests/exec/.gitignore @@ -9,8 +9,10 @@ execveat.ephemeral execveat.denatured non-regular null-argv +/false /load_address_* /recursion-depth +/should-exec xxxxxxxx* pipe S_I*.test diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile index fb4472ddffd8..fc0cb8925b02 100644 --- a/tools/testing/selftests/exec/Makefile +++ b/tools/testing/selftests/exec/Makefile @@ -2,15 +2,20 @@ CFLAGS = -Wall CFLAGS += -Wno-nonnull CFLAGS += -D_GNU_SOURCE +CFLAGS += $(KHDR_INCLUDES) + +LDLIBS += -lcap TEST_PROGS := binfmt_script.py TEST_GEN_PROGS := execveat load_address_4096 load_address_2097152 load_address_16777216 non-regular +TEST_GEN_PROGS_EXTENDED := false TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir # Makefile is a run-time dependency, since it's accessed by the execveat test TEST_FILES := Makefile TEST_GEN_PROGS += recursion-depth TEST_GEN_PROGS += null-argv +TEST_GEN_PROGS += should-exec EXTRA_CLEAN := $(OUTPUT)/subdir.moved $(OUTPUT)/execveat.moved $(OUTPUT)/xxxxx* \ $(OUTPUT)/S_I*.test @@ -34,3 +39,6 @@ $(OUTPUT)/load_address_2097152: load_address.c $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x200000 -pie -static $< -o $@ $(OUTPUT)/load_address_16777216: load_address.c $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x1000000 -pie -static $< -o $@ + +$(OUTPUT)/false: false.c + $(CC) $(CFLAGS) $(LDFLAGS) -static $< -o $@ diff --git a/tools/testing/selftests/exec/config b/tools/testing/selftests/exec/config new file mode 100644 index 000000000000..c308079867b3 --- /dev/null +++ b/tools/testing/selftests/exec/config @@ -0,0 +1,2 @@ +CONFIG_BLK_DEV=y +CONFIG_BLK_DEV_LOOP=y diff --git a/tools/testing/selftests/exec/false.c b/tools/testing/selftests/exec/false.c new file mode 100644 index 000000000000..104383ec3a79 --- /dev/null +++ b/tools/testing/selftests/exec/false.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0 +int main(void) +{ + return 1; +} diff --git a/tools/testing/selftests/exec/should-exec.c b/tools/testing/selftests/exec/should-exec.c new file mode 100644 index 000000000000..166276a39b4e --- /dev/null +++ b/tools/testing/selftests/exec/should-exec.c @@ -0,0 +1,449 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Test execveat(2) with AT_CHECK, and prctl(2) with SECBIT_SHOULD_EXEC_CHECK, + * SECBIT_SHOULD_EXEC_RESTRIC, and their locked counterparts. + * + * Copyright © 2018-2020 ANSSI + * Copyright © 2024 Microsoft Corporation + * + * Author: Mickaël Salaün <mic@xxxxxxxxxxx> + */ + +#include <asm-generic/unistd.h> +#include <errno.h> +#include <fcntl.h> +#include <linux/prctl.h> +#include <linux/securebits.h> +#include <stdio.h> +#include <stdlib.h> +#include <sys/capability.h> +#include <sys/mount.h> +#include <sys/prctl.h> +#include <sys/socket.h> +#include <sys/stat.h> +#include <sys/sysmacros.h> +#include <unistd.h> + +/* Defines AT_CHECK without type conflicts. */ +#define _ASM_GENERIC_FCNTL_H +#include <linux/fcntl.h> + +#include "../kselftest_harness.h" + +static void drop_privileges(struct __test_metadata *const _metadata) +{ + const unsigned int noroot = SECBIT_NOROOT | SECBIT_NOROOT_LOCKED; + cap_t cap_p; + + if ((cap_get_secbits() & noroot) != noroot) + EXPECT_EQ(0, cap_set_secbits(noroot)); + + cap_p = cap_get_proc(); + EXPECT_NE(NULL, cap_p); + EXPECT_NE(-1, cap_clear(cap_p)); + + /* + * Drops everything, especially CAP_SETPCAP, CAP_DAC_OVERRIDE, and + * CAP_DAC_READ_SEARCH. + */ + EXPECT_NE(-1, cap_set_proc(cap_p)); + EXPECT_NE(-1, cap_free(cap_p)); +} + +static int test_secbits_set(const unsigned int secbits) +{ + int err; + + err = prctl(PR_SET_SECUREBITS, secbits); + if (err) + return errno; + return 0; +} + +FIXTURE(access) +{ + int memfd, pipefd; + int pipe_fds[2], socket_fds[2]; +}; + +FIXTURE_VARIANT(access) +{ + const bool mount_exec; + const bool file_exec; +}; + +FIXTURE_VARIANT_ADD(access, mount_exec_file_exec){ + .mount_exec = true, + .file_exec = true, +}; + +FIXTURE_VARIANT_ADD(access, mount_exec_file_noexec){ + .mount_exec = true, + .file_exec = false, +}; + +FIXTURE_VARIANT_ADD(access, mount_noexec_file_exec){ + .mount_exec = false, + .file_exec = true, +}; + +FIXTURE_VARIANT_ADD(access, mount_noexec_file_noexec){ + .mount_exec = false, + .file_exec = false, +}; + +static const char binary_path[] = "./false"; +static const char workdir_path[] = "./test-mount"; +static const char reg_file_path[] = "./test-mount/regular_file"; +static const char dir_path[] = "./test-mount/directory"; +static const char block_dev_path[] = "./test-mount/block_device"; +static const char char_dev_path[] = "./test-mount/character_device"; +static const char fifo_path[] = "./test-mount/fifo"; + +FIXTURE_SETUP(access) +{ + int procfd_path_size; + static const char path_template[] = "/proc/self/fd/%d"; + char procfd_path[sizeof(path_template) + 10]; + + /* Makes sure we are not already restricted nor locked. */ + EXPECT_EQ(0, test_secbits_set(0)); + + /* + * Cleans previous workspace if any error previously happened (don't + * check errors). + */ + umount(workdir_path); + rmdir(workdir_path); + + /* Creates a clean mount point. */ + ASSERT_EQ(0, mkdir(workdir_path, 00700)); + ASSERT_EQ(0, mount("test", workdir_path, "tmpfs", + MS_MGC_VAL | (variant->mount_exec ? 0 : MS_NOEXEC), + "mode=0700,size=9m")); + + /* Creates a regular file. */ + ASSERT_EQ(0, mknod(reg_file_path, + S_IFREG | (variant->file_exec ? 0700 : 0600), 0)); + /* Creates a directory. */ + ASSERT_EQ(0, mkdir(dir_path, variant->file_exec ? 0700 : 0600)); + /* Creates a character device: /dev/null. */ + ASSERT_EQ(0, mknod(char_dev_path, S_IFCHR | 0400, makedev(1, 3))); + /* Creates a block device: /dev/loop0 */ + ASSERT_EQ(0, mknod(block_dev_path, S_IFBLK | 0400, makedev(7, 0))); + /* Creates a fifo. */ + ASSERT_EQ(0, mknod(fifo_path, S_IFIFO | 0600, 0)); + + /* Creates a regular file without user mount point. */ + self->memfd = memfd_create("test-exec-probe", MFD_CLOEXEC); + ASSERT_LE(0, self->memfd); + /* Sets mode, which must be ignored by the exec check. */ + ASSERT_EQ(0, fchmod(self->memfd, variant->file_exec ? 0700 : 0600)); + + /* Creates a pipefs file descriptor. */ + ASSERT_EQ(0, pipe(self->pipe_fds)); + procfd_path_size = snprintf(procfd_path, sizeof(procfd_path), + path_template, self->pipe_fds[0]); + ASSERT_LT(procfd_path_size, sizeof(procfd_path)); + self->pipefd = open(procfd_path, O_RDWR | O_CLOEXEC); + ASSERT_LE(0, self->pipefd); + ASSERT_EQ(0, fchmod(self->pipefd, variant->file_exec ? 0700 : 0600)); + + /* Creates a socket file descriptor. */ + ASSERT_EQ(0, socketpair(AF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0, + self->socket_fds)); +} + +FIXTURE_TEARDOWN_PARENT(access) +{ + /* There is no need to unlink the test files. */ + EXPECT_EQ(0, umount(workdir_path)); + EXPECT_EQ(0, rmdir(workdir_path)); +} + +static void fill_exec_fd(struct __test_metadata *_metadata, const int fd_out) +{ + char buf[1024]; + size_t len; + int fd_in; + + fd_in = open(binary_path, O_CLOEXEC | O_RDONLY); + ASSERT_LE(0, fd_in); + /* Cannot use copy_file_range(2) because of EXDEV. */ + len = read(fd_in, buf, sizeof(buf)); + EXPECT_LE(0, len); + while (len > 0) { + EXPECT_EQ(len, write(fd_out, buf, len)) + { + TH_LOG("Failed to write: %s (%d)", strerror(errno), + errno); + } + len = read(fd_in, buf, sizeof(buf)); + EXPECT_LE(0, len); + } + EXPECT_EQ(0, close(fd_in)); +} + +static void fill_exec_path(struct __test_metadata *_metadata, + const char *const path) +{ + int fd_out; + + fd_out = open(path, O_CLOEXEC | O_WRONLY); + ASSERT_LE(0, fd_out) + { + TH_LOG("Failed to open %s: %s", path, strerror(errno)); + } + fill_exec_fd(_metadata, fd_out); + EXPECT_EQ(0, close(fd_out)); +} + +static void test_exec_fd(struct __test_metadata *_metadata, const int fd, + const int err_code) +{ + char *const argv[] = { "", NULL }; + int access_ret, access_errno; + + /* + * If we really execute fd, filled with the "false" binary, the current + * thread will exits with an error, which will be interpreted by the + * test framework as an error. With AT_CHECK, we only check a + * potential successful execution. + */ + access_ret = execveat(fd, "", argv, NULL, AT_EMPTY_PATH | AT_CHECK); + access_errno = errno; + if (err_code) { + EXPECT_EQ(-1, access_ret); + EXPECT_EQ(err_code, access_errno) + { + TH_LOG("Wrong error for execveat(2): %s (%d)", + strerror(access_errno), errno); + } + } else { + EXPECT_EQ(0, access_ret) + { + TH_LOG("Access denied: %s", strerror(access_errno)); + } + } +} + +static void test_exec_path(struct __test_metadata *_metadata, + const char *const path, const int err_code) +{ + int flags = O_CLOEXEC; + int fd; + + /* Do not block on pipes. */ + if (path == fifo_path) + flags |= O_NONBLOCK; + + fd = open(path, flags | O_RDONLY); + ASSERT_LE(0, fd) + { + TH_LOG("Failed to open %s: %s", path, strerror(errno)); + } + test_exec_fd(_metadata, fd, err_code); + EXPECT_EQ(0, close(fd)); +} + +/* Tests that we don't get ENOEXEC. */ +TEST_F(access, regular_file_empty) +{ + const int exec = variant->mount_exec && variant->file_exec; + + test_exec_path(_metadata, reg_file_path, exec ? 0 : EACCES); + + drop_privileges(_metadata); + test_exec_path(_metadata, reg_file_path, exec ? 0 : EACCES); +} + +TEST_F(access, regular_file_elf) +{ + const int exec = variant->mount_exec && variant->file_exec; + + fill_exec_path(_metadata, reg_file_path); + + test_exec_path(_metadata, reg_file_path, exec ? 0 : EACCES); + + drop_privileges(_metadata); + test_exec_path(_metadata, reg_file_path, exec ? 0 : EACCES); +} + +/* Tests that we don't get ENOEXEC. */ +TEST_F(access, memfd_empty) +{ + const int exec = variant->file_exec; + + test_exec_fd(_metadata, self->memfd, exec ? 0 : EACCES); + + drop_privileges(_metadata); + test_exec_fd(_metadata, self->memfd, exec ? 0 : EACCES); +} + +TEST_F(access, memfd_elf) +{ + const int exec = variant->file_exec; + + fill_exec_fd(_metadata, self->memfd); + + test_exec_fd(_metadata, self->memfd, exec ? 0 : EACCES); + + drop_privileges(_metadata); + test_exec_fd(_metadata, self->memfd, exec ? 0 : EACCES); +} + +TEST_F(access, non_regular_files) +{ + test_exec_path(_metadata, dir_path, EACCES); + test_exec_path(_metadata, block_dev_path, EACCES); + test_exec_path(_metadata, char_dev_path, EACCES); + test_exec_path(_metadata, fifo_path, EACCES); + test_exec_fd(_metadata, self->socket_fds[0], EACCES); + test_exec_fd(_metadata, self->pipefd, EACCES); +} + + +/* clang-format off */ +FIXTURE(secbits) {}; +/* clang-format on */ + +FIXTURE_VARIANT(secbits) +{ + const bool is_privileged; + const int error; +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(secbits, priv) { + /* clang-format on */ + .is_privileged = true, + .error = 0, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(secbits, unpriv) { + /* clang-format on */ + .is_privileged = false, + .error = EPERM, +}; + +FIXTURE_SETUP(secbits) +{ + /* Makes sure no should-exec bits are set. */ + EXPECT_EQ(0, test_secbits_set(0)); + EXPECT_EQ(0, prctl(PR_GET_SECUREBITS)); + + if (!variant->is_privileged) + drop_privileges(_metadata); +} + +FIXTURE_TEARDOWN(secbits) +{ +} + +TEST_F(secbits, legacy) +{ + EXPECT_EQ(variant->error, test_secbits_set(0)); +} + +#define CHILD(...) \ + do { \ + pid_t child = vfork(); \ + EXPECT_LE(0, child); \ + if (child == 0) { \ + __VA_ARGS__; \ + _exit(0); \ + } \ + } while (0) + +TEST_F(secbits, should_exec) +{ + unsigned int secbits = prctl(PR_GET_SECUREBITS); + + secbits |= SECBIT_SHOULD_EXEC_CHECK; + EXPECT_EQ(0, test_secbits_set(secbits)); + EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS)); + CHILD(EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS))); + + secbits |= SECBIT_SHOULD_EXEC_RESTRICT; + EXPECT_EQ(0, test_secbits_set(secbits)); + EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS)); + CHILD(EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS))); + + secbits &= ~(SECBIT_SHOULD_EXEC_CHECK | SECBIT_SHOULD_EXEC_RESTRICT); + EXPECT_EQ(0, test_secbits_set(secbits)); + EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS)); + CHILD(EXPECT_EQ(secbits, prctl(PR_GET_SECUREBITS))); +} + +TEST_F(secbits, check_locked_set) +{ + unsigned int secbits = prctl(PR_GET_SECUREBITS); + + secbits |= SECBIT_SHOULD_EXEC_CHECK; + EXPECT_EQ(0, test_secbits_set(secbits)); + secbits |= SECBIT_SHOULD_EXEC_CHECK_LOCKED; + EXPECT_EQ(0, test_secbits_set(secbits)); + + /* Checks lock set but unchanged. */ + EXPECT_EQ(variant->error, test_secbits_set(secbits)); + CHILD(EXPECT_EQ(variant->error, test_secbits_set(secbits))); + + secbits &= ~SECBIT_SHOULD_EXEC_CHECK; + EXPECT_EQ(EPERM, test_secbits_set(0)); + CHILD(EXPECT_EQ(EPERM, test_secbits_set(0))); +} + +TEST_F(secbits, check_locked_unset) +{ + unsigned int secbits = prctl(PR_GET_SECUREBITS); + + secbits |= SECBIT_SHOULD_EXEC_CHECK_LOCKED; + EXPECT_EQ(0, test_secbits_set(secbits)); + + /* Checks lock unset but unchanged. */ + EXPECT_EQ(variant->error, test_secbits_set(secbits)); + CHILD(EXPECT_EQ(variant->error, test_secbits_set(secbits))); + + secbits &= ~SECBIT_SHOULD_EXEC_CHECK; + EXPECT_EQ(EPERM, test_secbits_set(0)); + CHILD(EXPECT_EQ(EPERM, test_secbits_set(0))); +} + +TEST_F(secbits, restrict_locked_set) +{ + unsigned int secbits = prctl(PR_GET_SECUREBITS); + + secbits |= SECBIT_SHOULD_EXEC_RESTRICT; + EXPECT_EQ(0, test_secbits_set(secbits)); + secbits |= SECBIT_SHOULD_EXEC_RESTRICT_LOCKED; + EXPECT_EQ(0, test_secbits_set(secbits)); + + /* Checks lock set but unchanged. */ + EXPECT_EQ(variant->error, test_secbits_set(secbits)); + CHILD(EXPECT_EQ(variant->error, test_secbits_set(secbits))); + + secbits &= ~SECBIT_SHOULD_EXEC_RESTRICT; + EXPECT_EQ(EPERM, test_secbits_set(0)); + CHILD(EXPECT_EQ(EPERM, test_secbits_set(0))); +} + +TEST_F(secbits, restrict_locked_unset) +{ + unsigned int secbits = prctl(PR_GET_SECUREBITS); + + secbits |= SECBIT_SHOULD_EXEC_RESTRICT_LOCKED; + EXPECT_EQ(0, test_secbits_set(secbits)); + + /* Checks lock unset but unchanged. */ + EXPECT_EQ(variant->error, test_secbits_set(secbits)); + CHILD(EXPECT_EQ(variant->error, test_secbits_set(secbits))); + + secbits &= ~SECBIT_SHOULD_EXEC_RESTRICT; + EXPECT_EQ(EPERM, test_secbits_set(0)); + CHILD(EXPECT_EQ(EPERM, test_secbits_set(0))); +} + +/* TODO: Add ptrace tests */ + +TEST_HARNESS_MAIN -- 2.45.2
