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    Subject[PATCH v12 3/3] selftest/interpreter: Add tests for trusted_for(2) policies
    Date
    From: Mickaël Salaün <mic@linux.microsoft.com>

    Test that checks performed by trusted_for(2) on file descriptors are
    consistent with noexec mount points and file execute permissions,
    according to the policy configured with the fs.trust_policy sysctl.

    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Shuah Khan <shuah@kernel.org>
    Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
    Reviewed-by: Thibaut Sautereau <thibaut.sautereau@ssi.gouv.fr>
    ---

    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/Makefile | 1 +
    .../testing/selftests/interpreter/.gitignore | 2 +
    tools/testing/selftests/interpreter/Makefile | 21 +
    tools/testing/selftests/interpreter/config | 1 +
    .../selftests/interpreter/trust_policy_test.c | 362 ++++++++++++++++++
    5 files changed, 387 insertions(+)
    create mode 100644 tools/testing/selftests/interpreter/.gitignore
    create mode 100644 tools/testing/selftests/interpreter/Makefile
    create mode 100644 tools/testing/selftests/interpreter/config
    create mode 100644 tools/testing/selftests/interpreter/trust_policy_test.c

    diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
    index d9c283503159..9e18244abc5d 100644
    --- a/tools/testing/selftests/Makefile
    +++ b/tools/testing/selftests/Makefile
    @@ -21,6 +21,7 @@ TARGETS += ftrace
    TARGETS += futex
    TARGETS += gpio
    TARGETS += intel_pstate
    +TARGETS += interpreter
    TARGETS += ipc
    TARGETS += ir
    TARGETS += kcmp
    diff --git a/tools/testing/selftests/interpreter/.gitignore b/tools/testing/selftests/interpreter/.gitignore
    new file mode 100644
    index 000000000000..82a4846cbc4b
    --- /dev/null
    +++ b/tools/testing/selftests/interpreter/.gitignore
    @@ -0,0 +1,2 @@
    +# SPDX-License-Identifier: GPL-2.0-only
    +/*_test
    diff --git a/tools/testing/selftests/interpreter/Makefile b/tools/testing/selftests/interpreter/Makefile
    new file mode 100644
    index 000000000000..dbca8ebda67e
    --- /dev/null
    +++ b/tools/testing/selftests/interpreter/Makefile
    @@ -0,0 +1,21 @@
    +# SPDX-License-Identifier: GPL-2.0-or-later
    +
    +CFLAGS += -Wall -O2
    +LDLIBS += -lcap
    +
    +src_test := $(wildcard *_test.c)
    +TEST_GEN_PROGS := $(src_test:.c=)
    +
    +KSFT_KHDR_INSTALL := 1
    +include ../lib.mk
    +
    +khdr_dir = $(top_srcdir)/usr/include
    +
    +$(khdr_dir)/asm-generic/unistd.h: khdr
    + @:
    +
    +$(khdr_dir)/linux/trusted-for.h: khdr
    + @:
    +
    +$(OUTPUT)/%_test: %_test.c $(khdr_dir)/asm-generic/unistd.h $(khdr_dir)/linux/trusted-for.h ../kselftest_harness.h
    + $(LINK.c) $< $(LDLIBS) -o $@ -I$(khdr_dir)
    diff --git a/tools/testing/selftests/interpreter/config b/tools/testing/selftests/interpreter/config
    new file mode 100644
    index 000000000000..dd53c266bf52
    --- /dev/null
    +++ b/tools/testing/selftests/interpreter/config
    @@ -0,0 +1 @@
    +CONFIG_SYSCTL=y
    diff --git a/tools/testing/selftests/interpreter/trust_policy_test.c b/tools/testing/selftests/interpreter/trust_policy_test.c
    new file mode 100644
    index 000000000000..4818c5524ec0
    --- /dev/null
    +++ b/tools/testing/selftests/interpreter/trust_policy_test.c
    @@ -0,0 +1,362 @@
    +// SPDX-License-Identifier: GPL-2.0
    +/*
    + * Test trusted_for(2) with fs.trust_policy sysctl
    + *
    + * Copyright © 2018-2020 ANSSI
    + *
    + * Author: Mickaël Salaün <mic@digikod.net>
    + */
    +
    +#define _GNU_SOURCE
    +#include <asm-generic/unistd.h>
    +#include <errno.h>
    +#include <fcntl.h>
    +#include <linux/trusted-for.h>
    +#include <stdio.h>
    +#include <stdlib.h>
    +#include <sys/capability.h>
    +#include <sys/mman.h>
    +#include <sys/mount.h>
    +#include <sys/socket.h>
    +#include <sys/stat.h>
    +#include <sys/syscall.h>
    +#include <sys/sysmacros.h>
    +#include <sys/types.h>
    +#include <unistd.h>
    +
    +#include "../kselftest_harness.h"
    +
    +#ifndef trusted_for
    +static int trusted_for(const int fd, const enum trusted_for_usage usage,
    + const __u32 flags)
    +{
    + errno = 0;
    + return syscall(__NR_trusted_for, fd, usage, flags);
    +}
    +#endif
    +
    +static const char sysctl_path[] = "/proc/sys/fs/trust_policy";
    +
    +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";
    +
    +static void ignore_dac(struct __test_metadata *_metadata, int override)
    +{
    + cap_t caps;
    + const cap_value_t cap_val[2] = {
    + CAP_DAC_OVERRIDE,
    + CAP_DAC_READ_SEARCH,
    + };
    +
    + caps = cap_get_proc();
    + ASSERT_NE(NULL, caps);
    + ASSERT_EQ(0, cap_set_flag(caps, CAP_EFFECTIVE, 2, cap_val,
    + override ? CAP_SET : CAP_CLEAR));
    + ASSERT_EQ(0, cap_set_proc(caps));
    + EXPECT_EQ(0, cap_free(caps));
    +}
    +
    +static void ignore_sys_admin(struct __test_metadata *_metadata, int override)
    +{
    + cap_t caps;
    + const cap_value_t cap_val[1] = {
    + CAP_SYS_ADMIN,
    + };
    +
    + caps = cap_get_proc();
    + ASSERT_NE(NULL, caps);
    + ASSERT_EQ(0, cap_set_flag(caps, CAP_EFFECTIVE, 1, cap_val,
    + override ? CAP_SET : CAP_CLEAR));
    + ASSERT_EQ(0, cap_set_proc(caps));
    + EXPECT_EQ(0, cap_free(caps));
    +}
    +
    +static void test_omx(struct __test_metadata *_metadata,
    + const char *const path, const int err_access)
    +{
    + int flags = O_RDONLY | O_CLOEXEC;
    + int fd, access_ret, access_errno;
    +
    + /* Do not block on pipes. */
    + if (path == fifo_path)
    + flags |= O_NONBLOCK;
    +
    + fd = open(path, flags);
    + ASSERT_LE(0, fd) {
    + TH_LOG("Failed to open %s: %s", path, strerror(errno));
    + }
    + access_ret = trusted_for(fd, TRUSTED_FOR_EXECUTION, 0);
    + access_errno = errno;
    + if (err_access) {
    + ASSERT_EQ(err_access, access_errno) {
    + TH_LOG("Wrong error for trusted_for(2) with %s: %s",
    + path, strerror(access_errno));
    + }
    + ASSERT_EQ(-1, access_ret);
    + } else {
    + ASSERT_EQ(0, access_ret) {
    + TH_LOG("Access denied for %s: %s", path, strerror(access_errno));
    + }
    + }
    +
    + /* Tests unsupported trusted usage. */
    + access_ret = trusted_for(fd, 0, 0);
    + ASSERT_EQ(-1, access_ret);
    + ASSERT_EQ(EINVAL, errno);
    +
    + access_ret = trusted_for(fd, 2, 0);
    + ASSERT_EQ(-1, access_ret);
    + ASSERT_EQ(EINVAL, errno);
    +
    + EXPECT_EQ(0, close(fd));
    +}
    +
    +static void test_policy_fd(struct __test_metadata *_metadata, const int fd,
    + const bool has_policy)
    +{
    + const int ret = trusted_for(fd, TRUSTED_FOR_EXECUTION, 0);
    +
    + if (has_policy) {
    + ASSERT_EQ(-1, ret);
    + ASSERT_EQ(EACCES, errno) {
    + TH_LOG("Wrong error for trusted_for(2) with FD: %s", strerror(errno));
    + }
    + } else {
    + ASSERT_EQ(0, ret) {
    + TH_LOG("Access denied for FD: %s", strerror(errno));
    + }
    + }
    +}
    +
    +FIXTURE(access) {
    + char initial_sysctl_value;
    + int memfd, pipefd;
    + int pipe_fds[2], socket_fds[2];
    +};
    +
    +static void test_file_types(struct __test_metadata *_metadata, FIXTURE_DATA(access) *self,
    + const int err_code, const bool has_policy)
    +{
    + /* Tests are performed on a tmpfs mount point. */
    + test_omx(_metadata, reg_file_path, err_code);
    + test_omx(_metadata, dir_path, has_policy ? EACCES : 0);
    + test_omx(_metadata, block_dev_path, has_policy ? EACCES : 0);
    + test_omx(_metadata, char_dev_path, has_policy ? EACCES : 0);
    + test_omx(_metadata, fifo_path, has_policy ? EACCES : 0);
    +
    + /* Checks that exec is denied for any socket FD. */
    + test_policy_fd(_metadata, self->socket_fds[0], has_policy);
    +
    + /* Checks that exec is denied for any memfd. */
    + test_policy_fd(_metadata, self->memfd, has_policy);
    +
    + /* Checks that exec is denied for any pipefs FD. */
    + test_policy_fd(_metadata, self->pipefd, has_policy);
    +}
    +
    +static void test_files(struct __test_metadata *_metadata, FIXTURE_DATA(access) *self,
    + const int err_code, const bool has_policy)
    +{
    + /* Tests as root. */
    + ignore_dac(_metadata, 1);
    + test_file_types(_metadata, self, err_code, has_policy);
    +
    + /* Tests without bypass. */
    + ignore_dac(_metadata, 0);
    + test_file_types(_metadata, self, err_code, has_policy);
    +}
    +
    +static void sysctl_write_char(struct __test_metadata *_metadata, const char value)
    +{
    + int fd;
    +
    + fd = open(sysctl_path, O_WRONLY | O_CLOEXEC);
    + ASSERT_LE(0, fd);
    + ASSERT_EQ(1, write(fd, &value, 1));
    + EXPECT_EQ(0, close(fd));
    +}
    +
    +static char sysctl_read_char(struct __test_metadata *_metadata)
    +{
    + int fd;
    + char sysctl_value;
    +
    + fd = open(sysctl_path, O_RDONLY | O_CLOEXEC);
    + ASSERT_LE(0, fd);
    + ASSERT_EQ(1, read(fd, &sysctl_value, 1));
    + EXPECT_EQ(0, close(fd));
    + return sysctl_value;
    +}
    +
    +FIXTURE_VARIANT(access) {
    + const bool mount_exec;
    + const bool file_exec;
    + const int sysctl_err_code[3];
    +};
    +
    +FIXTURE_VARIANT_ADD(access, mount_exec_file_exec) {
    + .mount_exec = true,
    + .file_exec = true,
    + .sysctl_err_code = {0, 0, 0},
    +};
    +
    +FIXTURE_VARIANT_ADD(access, mount_exec_file_noexec)
    +{
    + .mount_exec = true,
    + .file_exec = false,
    + .sysctl_err_code = {0, EACCES, EACCES},
    +};
    +
    +FIXTURE_VARIANT_ADD(access, mount_noexec_file_exec)
    +{
    + .mount_exec = false,
    + .file_exec = true,
    + .sysctl_err_code = {EACCES, 0, EACCES},
    +};
    +
    +FIXTURE_VARIANT_ADD(access, mount_noexec_file_noexec)
    +{
    + .mount_exec = false,
    + .file_exec = false,
    + .sysctl_err_code = {EACCES, EACCES, EACCES},
    +};
    +
    +FIXTURE_SETUP(access)
    +{
    + int procfd_path_size;
    + static const char path_template[] = "/proc/self/fd/%d";
    + char procfd_path[sizeof(path_template) + 10];
    +
    + /*
    + * 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=4k"));
    +
    + /* Creates a regular file. */
    + ASSERT_EQ(0, mknod(reg_file_path, S_IFREG | (variant->file_exec ? 0500 : 0400), 0));
    + /* Creates a directory. */
    + ASSERT_EQ(0, mkdir(dir_path, variant->file_exec ? 0500 : 0400));
    + /* 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 | 0400, 0));
    +
    + /* Creates a regular file without user mount point. */
    + self->memfd = memfd_create("test-interpreted", 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 ? 0500 : 0400));
    +
    + /* 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_RDONLY | O_CLOEXEC);
    + ASSERT_LE(0, self->pipefd);
    + ASSERT_EQ(0, fchmod(self->pipefd, variant->file_exec ? 0500 : 0400));
    +
    + /* Creates a socket file descriptor. */
    + ASSERT_EQ(0, socketpair(AF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0, self->socket_fds));
    +
    + /* Saves initial sysctl value. */
    + self->initial_sysctl_value = sysctl_read_char(_metadata);
    +
    + /* Prepares for sysctl writes. */
    + ignore_sys_admin(_metadata, 1);
    +}
    +
    +FIXTURE_TEARDOWN(access)
    +{
    + EXPECT_EQ(0, close(self->memfd));
    + EXPECT_EQ(0, close(self->pipefd));
    + EXPECT_EQ(0, close(self->pipe_fds[0]));
    + EXPECT_EQ(0, close(self->pipe_fds[1]));
    + EXPECT_EQ(0, close(self->socket_fds[0]));
    + EXPECT_EQ(0, close(self->socket_fds[1]));
    +
    + /* Restores initial sysctl value. */
    + sysctl_write_char(_metadata, self->initial_sysctl_value);
    +
    + /* There is no need to unlink the test files. */
    + ASSERT_EQ(0, umount(workdir_path));
    + ASSERT_EQ(0, rmdir(workdir_path));
    +}
    +
    +TEST_F(access, sysctl_0)
    +{
    + /* Do not enforce anything. */
    + sysctl_write_char(_metadata, '0');
    + test_files(_metadata, self, 0, false);
    +}
    +
    +TEST_F(access, sysctl_1)
    +{
    + /* Enforces mount exec check. */
    + sysctl_write_char(_metadata, '1');
    + test_files(_metadata, self, variant->sysctl_err_code[0], true);
    +}
    +
    +TEST_F(access, sysctl_2)
    +{
    + /* Enforces file exec check. */
    + sysctl_write_char(_metadata, '2');
    + test_files(_metadata, self, variant->sysctl_err_code[1], true);
    +}
    +
    +TEST_F(access, sysctl_3)
    +{
    + /* Enforces mount and file exec check. */
    + sysctl_write_char(_metadata, '3');
    + test_files(_metadata, self, variant->sysctl_err_code[2], true);
    +}
    +
    +FIXTURE(cleanup) {
    + char initial_sysctl_value;
    +};
    +
    +FIXTURE_SETUP(cleanup)
    +{
    + /* Saves initial sysctl value. */
    + self->initial_sysctl_value = sysctl_read_char(_metadata);
    +}
    +
    +FIXTURE_TEARDOWN(cleanup)
    +{
    + /* Restores initial sysctl value. */
    + ignore_sys_admin(_metadata, 1);
    + sysctl_write_char(_metadata, self->initial_sysctl_value);
    +}
    +
    +TEST_F(cleanup, sysctl_access_write)
    +{
    + int fd;
    + ssize_t ret;
    +
    + ignore_sys_admin(_metadata, 1);
    + sysctl_write_char(_metadata, '0');
    +
    + ignore_sys_admin(_metadata, 0);
    + fd = open(sysctl_path, O_WRONLY | O_CLOEXEC);
    + ASSERT_LE(0, fd);
    + ret = write(fd, "0", 1);
    + ASSERT_EQ(-1, ret);
    + ASSERT_EQ(EPERM, errno);
    + EXPECT_EQ(0, close(fd));
    +}
    +
    +TEST_HARNESS_MAIN
    --
    2.29.2
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      Last update: 2020-12-03 18:35    [W:2.990 / U:0.004 seconds]
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