[PATCH v2 4/5] selftest/exec: Add tests for O_MAYEXEC enforcing

Mickaël Salaün
2019-09-06T15:27:19Z

Test propagation of noexec mount points or file executability through
files open with or without O_MAYEXEC.

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

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mickaël Salaün <mickael.salaun@ssi.gouv.fr>
Cc: Shuah Khan <shuah@kernel.org>
---
tools/testing/selftests/exec/.gitignore | 1 +
tools/testing/selftests/exec/Makefile | 4 +-
tools/testing/selftests/exec/omayexec.c | 317 ++++++++++++++++++++
tools/testing/selftests/kselftest_harness.h | 3 +
4 files changed, 324 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/exec/omayexec.c

diff --git a/tools/testing/selftests/exec/.gitignore b/tools/testing/selftests/exec/.gitignore
index b02279da6fa1..78487c987c07 100644
--- a/tools/testing/selftests/exec/.gitignore
+++ b/tools/testing/selftests/exec/.gitignore
@@ -1,3 +1,4 @@
+/omayexec
subdir*
script*
execveat
diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile
index 33339e31e365..a62b9ca306e7 100644
--- a/tools/testing/selftests/exec/Makefile
+++ b/tools/testing/selftests/exec/Makefile
@@ -3,7 +3,7 @@ CFLAGS = -Wall
CFLAGS += -Wno-nonnull
CFLAGS += -D_GNU_SOURCE

-TEST_GEN_PROGS := execveat
+TEST_GEN_PROGS := execveat omayexec
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
@@ -26,3 +26,5 @@ $(OUTPUT)/execveat.denatured: $(OUTPUT)/execveat
cp $< $@
chmod -x $@

+$(OUTPUT)/omayexec: omayexec.c ../kselftest_harness.h
+ $(CC) $(CFLAGS) -Wl,-no-as-needed $(LDFLAGS) -lcap $< -o $@
diff --git a/tools/testing/selftests/exec/omayexec.c b/tools/testing/selftests/exec/omayexec.c
new file mode 100644
index 000000000000..e4307b5a5417
--- /dev/null
+++ b/tools/testing/selftests/exec/omayexec.c
@@ -0,0 +1,317 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * O_MAYEXEC tests
+ *
+ * Copyright © 2018-2019 ANSSI
+ *
+ * Author: Mickaël Salaün <mic@digikod.net>
+ */
+
+#include <errno.h>
+#include <fcntl.h> /* O_CLOEXEC */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h> /* strlen */
+#include <sys/capability.h>
+#include <sys/mount.h>
+#include <sys/stat.h> /* mkdir */
+#include <unistd.h> /* unlink, rmdir */
+
+#include "../kselftest_harness.h"
+
+#ifndef O_MAYEXEC
+#define O_MAYEXEC 040000000
+#endif
+
+#define SYSCTL_MAYEXEC "/proc/sys/fs/open_mayexec_enforce"
+
+#define BIN_DIR "./test-mount"
+#define BIN_PATH BIN_DIR "/file"
+#define DIR_PATH BIN_DIR "/directory"
+
+#define ALLOWED 1
+#define DENIED 0
+
+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_TRUE(!!caps);
+ ASSERT_FALSE(cap_set_flag(caps, CAP_EFFECTIVE, 2, cap_val,
+ override ? CAP_SET : CAP_CLEAR));
+ ASSERT_FALSE(cap_set_proc(caps));
+ EXPECT_FALSE(cap_free(caps));
+}
+
+static void ignore_mac(struct __test_metadata *_metadata, int override)
+{
+ cap_t caps;
+ const cap_value_t cap_val[1] = {
+ CAP_MAC_ADMIN,
+ };
+
+ caps = cap_get_proc();
+ ASSERT_TRUE(!!caps);
+ ASSERT_FALSE(cap_set_flag(caps, CAP_EFFECTIVE, 1, cap_val,
+ override ? CAP_SET : CAP_CLEAR));
+ ASSERT_FALSE(cap_set_proc(caps));
+ EXPECT_FALSE(cap_free(caps));
+}
+
+static void test_omx(struct __test_metadata *_metadata,
+ const char *const path, const int exec_allowed)
+{
+ int fd;
+
+ /* without O_MAYEXEC */
+ fd = open(path, O_RDONLY | O_CLOEXEC);
+ ASSERT_NE(-1, fd);
+ EXPECT_FALSE(close(fd));
+
+ /* with O_MAYEXEC */
+ fd = open(path, O_RDONLY | O_CLOEXEC | O_MAYEXEC);
+ if (exec_allowed) {
+ /* open should succeed */
+ ASSERT_NE(-1, fd);
+ EXPECT_FALSE(close(fd));
+ } else {
+ /* open should return EACCES */
+ ASSERT_EQ(-1, fd);
+ ASSERT_EQ(EACCES, errno);
+ }
+}
+
+static void test_omx_dir_file(struct __test_metadata *_metadata,
+ const char *const dir_path, const char *const file_path,
+ const int exec_allowed)
+{
+ /*
+ * directory execution is always denied since commit 73601ea5b7b1
+ * ("fs/open.c: allow opening only regular files during execve()")
+ */
+ test_omx(_metadata, dir_path, DENIED);
+ test_omx(_metadata, file_path, exec_allowed);
+}
+
+static void test_dir_file(struct __test_metadata *_metadata,
+ const char *const dir_path, const char *const file_path,
+ const int exec_allowed)
+{
+ /* test as root */
+ ignore_dac(_metadata, 1);
+ test_omx_dir_file(_metadata, dir_path, file_path, exec_allowed);
+
+ /* test without bypass */
+ ignore_dac(_metadata, 0);
+ test_omx_dir_file(_metadata, dir_path, file_path, exec_allowed);
+}
+
+static void sysctl_write(struct __test_metadata *_metadata,
+ const char *path, const char *value)
+{
+ int fd;
+ size_t len_value;
+ ssize_t len_wrote;
+
+ fd = open(path, O_WRONLY | O_CLOEXEC);
+ ASSERT_NE(-1, fd);
+ len_value = strlen(value);
+ len_wrote = write(fd, value, len_value);
+ ASSERT_EQ(len_wrote, len_value);
+ EXPECT_FALSE(close(fd));
+}
+
+static void create_workspace(struct __test_metadata *_metadata,
+ int mount_exec, int file_exec)
+{
+ int fd;
+
+ /*
+ * Cleanup previous workspace if any error previously happened (don't
+ * check errors).
+ */
+ umount(BIN_DIR);
+ rmdir(BIN_DIR);
+
+ /* create a clean mount point */
+ ASSERT_FALSE(mkdir(BIN_DIR, 00700));
+ ASSERT_FALSE(mount("test", BIN_DIR, "tmpfs",
+ MS_MGC_VAL | (mount_exec ? 0 : MS_NOEXEC),
+ "mode=0700,size=4k"));
+
+ /* create a test file */
+ fd = open(BIN_PATH, O_CREAT | O_RDONLY | O_CLOEXEC,
+ file_exec ? 00500 : 00400);
+ ASSERT_NE(-1, fd);
+ EXPECT_NE(-1, close(fd));
+
+ /* create a test directory */
+ ASSERT_FALSE(mkdir(DIR_PATH, file_exec ? 00500 : 00400));
+}
+
+static void delete_workspace(struct __test_metadata *_metadata)
+{
+ ignore_mac(_metadata, 1);
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "0");
+
+ /* no need to unlink BIN_PATH nor DIR_PATH */
+ ASSERT_FALSE(umount(BIN_DIR));
+ ASSERT_FALSE(rmdir(BIN_DIR));
+}
+
+FIXTURE_DATA(mount_exec_file_exec) { };
+
+FIXTURE_SETUP(mount_exec_file_exec)
+{
+ create_workspace(_metadata, 1, 1);
+}
+
+FIXTURE_TEARDOWN(mount_exec_file_exec)
+{
+ delete_workspace(_metadata);
+}
+
+TEST_F(mount_exec_file_exec, mount)
+{
+ /* enforce mount exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "1");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, ALLOWED);
+}
+
+TEST_F(mount_exec_file_exec, file)
+{
+ /* enforce file exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "2");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, ALLOWED);
+}
+
+TEST_F(mount_exec_file_exec, mount_file)
+{
+ /* enforce mount and file exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "3");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, ALLOWED);
+}
+
+FIXTURE_DATA(mount_exec_file_noexec) { };
+
+FIXTURE_SETUP(mount_exec_file_noexec)
+{
+ create_workspace(_metadata, 1, 0);
+}
+
+FIXTURE_TEARDOWN(mount_exec_file_noexec)
+{
+ delete_workspace(_metadata);
+}
+
+TEST_F(mount_exec_file_noexec, mount)
+{
+ /* enforce mount exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "1");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, ALLOWED);
+}
+
+TEST_F(mount_exec_file_noexec, file)
+{
+ /* enforce file exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "2");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, DENIED);
+}
+
+TEST_F(mount_exec_file_noexec, mount_file)
+{
+ /* enforce mount and file exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "3");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, DENIED);
+}
+
+FIXTURE_DATA(mount_noexec_file_exec) { };
+
+FIXTURE_SETUP(mount_noexec_file_exec)
+{
+ create_workspace(_metadata, 0, 1);
+}
+
+FIXTURE_TEARDOWN(mount_noexec_file_exec)
+{
+ delete_workspace(_metadata);
+}
+
+TEST_F(mount_noexec_file_exec, mount)
+{
+ /* enforce mount exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "1");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, DENIED);
+}
+
+TEST_F(mount_noexec_file_exec, file)
+{
+ /* enforce file exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "2");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, ALLOWED);
+}
+
+TEST_F(mount_noexec_file_exec, mount_file)
+{
+ /* enforce mount and file exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "3");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, DENIED);
+}
+
+FIXTURE_DATA(mount_noexec_file_noexec) { };
+
+FIXTURE_SETUP(mount_noexec_file_noexec)
+{
+ create_workspace(_metadata, 0, 0);
+}
+
+FIXTURE_TEARDOWN(mount_noexec_file_noexec)
+{
+ delete_workspace(_metadata);
+}
+
+TEST_F(mount_noexec_file_noexec, mount)
+{
+ /* enforce mount exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "1");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, DENIED);
+}
+
+TEST_F(mount_noexec_file_noexec, file)
+{
+ /* enforce file exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "2");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, DENIED);
+}
+
+TEST_F(mount_noexec_file_noexec, mount_file)
+{
+ /* enforce mount and file exec check */
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "3");
+ test_dir_file(_metadata, DIR_PATH, BIN_PATH, DENIED);
+}
+
+TEST(sysctl_access_write)
+{
+ int fd;
+ ssize_t len_wrote;
+
+ ignore_mac(_metadata, 1);
+ sysctl_write(_metadata, SYSCTL_MAYEXEC, "0");
+
+ ignore_mac(_metadata, 0);
+ fd = open(SYSCTL_MAYEXEC, O_WRONLY | O_CLOEXEC);
+ ASSERT_NE(-1, fd);
+ len_wrote = write(fd, "0", 1);
+ ASSERT_EQ(len_wrote, -1);
+ EXPECT_FALSE(close(fd));
+
+ ignore_mac(_metadata, 1);
+}
+
+TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index 5336b26506ab..6ae816fa2f62 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -50,7 +50,10 @@
#ifndef __KSELFTEST_HARNESS_H
#define __KSELFTEST_HARNESS_H

+#ifndef _GNU_SOURCE
#define _GNU_SOURCE
+#endif
+
#include <asm/types.h>
#include <errno.h>
#include <stdbool.h>
--
2.23.0