Test propagation of noexec mount points or file executability through files open with or without O_MAYEXEC, thanks to the fs.open_mayexec_enforce sysctl.
Signed-off-by: Mickaël Salaün <[email protected]> Reviewed-by: Thibaut Sautereau <[email protected]> Cc: Aleksa Sarai <[email protected]> Cc: Al Viro <[email protected]> Cc: Kees Cook <[email protected]> Cc: Shuah Khan <[email protected]> --- 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/kselftest_harness.h | 3 + tools/testing/selftests/openat2/Makefile | 3 +- tools/testing/selftests/openat2/config | 1 + tools/testing/selftests/openat2/helpers.h | 1 + .../testing/selftests/openat2/omayexec_test.c | 262 ++++++++++++++++++ 5 files changed, 269 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/openat2/config create mode 100644 tools/testing/selftests/openat2/omayexec_test.c diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h index c9f03ef93338..68a0acd9ea1e 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> diff --git a/tools/testing/selftests/openat2/Makefile b/tools/testing/selftests/openat2/Makefile index 4b93b1417b86..cb98bdb4d5b1 100644 --- a/tools/testing/selftests/openat2/Makefile +++ b/tools/testing/selftests/openat2/Makefile @@ -1,7 +1,8 @@ # SPDX-License-Identifier: GPL-2.0-or-later CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined -TEST_GEN_PROGS := openat2_test resolve_test rename_attack_test +LDLIBS += -lcap +TEST_GEN_PROGS := openat2_test resolve_test rename_attack_test omayexec_test include ../lib.mk diff --git a/tools/testing/selftests/openat2/config b/tools/testing/selftests/openat2/config new file mode 100644 index 000000000000..dd53c266bf52 --- /dev/null +++ b/tools/testing/selftests/openat2/config @@ -0,0 +1 @@ +CONFIG_SYSCTL=y diff --git a/tools/testing/selftests/openat2/helpers.h b/tools/testing/selftests/openat2/helpers.h index a6ea27344db2..1dcd3e1e2f38 100644 --- a/tools/testing/selftests/openat2/helpers.h +++ b/tools/testing/selftests/openat2/helpers.h @@ -9,6 +9,7 @@ #define _GNU_SOURCE #include <stdint.h> +#include <stdbool.h> #include <errno.h> #include <linux/types.h> #include "../kselftest.h" diff --git a/tools/testing/selftests/openat2/omayexec_test.c b/tools/testing/selftests/openat2/omayexec_test.c new file mode 100644 index 000000000000..a33f31e59045 --- /dev/null +++ b/tools/testing/selftests/openat2/omayexec_test.c @@ -0,0 +1,262 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Test O_MAYEXEC + * + * Copyright © 2018-2020 ANSSI + * + * Author: Mickaël Salaün <[email protected]> + */ + +#include <errno.h> +#include <fcntl.h> +#include <stdio.h> +#include <stdlib.h> +#include <sys/capability.h> +#include <sys/mount.h> +#include <sys/stat.h> +#include <unistd.h> + +#include "helpers.h" +#include "../kselftest_harness.h" + +#ifndef O_MAYEXEC +#define O_MAYEXEC 040000000 +#endif + +static const char sysctl_path[] = "/proc/sys/fs/open_mayexec_enforce"; + +static const char workdir_path[] = "./test-mount"; +static const char file_path[] = "./test-mount/file"; +static const char dir_path[] = "./test-mount/directory"; + +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_code) +{ + struct open_how how = { + .flags = O_RDONLY | O_CLOEXEC, + }; + int fd; + + /* Opens without O_MAYEXEC. */ + fd = sys_openat2(AT_FDCWD, path, &how); + ASSERT_LE(0, fd); + EXPECT_EQ(0, close(fd)); + + how.flags |= O_MAYEXEC; + + /* Checks that O_MAYEXEC is ignored with open(2). */ + fd = open(path, how.flags); + ASSERT_LE(0, fd); + EXPECT_EQ(0, close(fd)); + + /* Checks that O_MAYEXEC is ignored with openat(2). */ + fd = openat(AT_FDCWD, path, how.flags); + ASSERT_LE(0, fd); + EXPECT_EQ(0, close(fd)); + + /* Opens with O_MAYEXEC. */ + fd = sys_openat2(AT_FDCWD, path, &how); + if (!err_code) { + ASSERT_LE(0, fd); + EXPECT_EQ(0, close(fd)); + } else { + ASSERT_EQ(err_code, fd); + } +} + +static void test_omx_dir_file(struct __test_metadata *_metadata, const int err_code) +{ + test_omx(_metadata, dir_path, -EISDIR); + test_omx(_metadata, file_path, err_code); +} + +static void test_dir_file(struct __test_metadata *_metadata, const int err_code) +{ + /* Tests as root. */ + ignore_dac(_metadata, 1); + test_omx_dir_file(_metadata, err_code); + + /* Tests without bypass. */ + ignore_dac(_metadata, 0); + test_omx_dir_file(_metadata, err_code); +} + +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(omayexec) { + char initial_sysctl_value; +}; + +FIXTURE_VARIANT(omayexec) { + const bool mount_exec; + const bool file_exec; + const int sysctl_err_code[3]; +}; + +FIXTURE_VARIANT_ADD(omayexec, mount_exec_file_exec) { + .mount_exec = true, + .file_exec = true, + .sysctl_err_code = {0, 0, 0}, +}; + +FIXTURE_VARIANT_ADD(omayexec, mount_exec_file_noexec) +{ + .mount_exec = true, + .file_exec = false, + .sysctl_err_code = {0, -EACCES, -EACCES}, +}; + +FIXTURE_VARIANT_ADD(omayexec, mount_noexec_file_exec) +{ + .mount_exec = false, + .file_exec = true, + .sysctl_err_code = {-EACCES, 0, -EACCES}, +}; + +FIXTURE_VARIANT_ADD(omayexec, mount_noexec_file_noexec) +{ + .mount_exec = false, + .file_exec = false, + .sysctl_err_code = {-EACCES, -EACCES, -EACCES}, +}; + +FIXTURE_SETUP(omayexec) +{ + int fd; + + /* + * 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 test file. */ + fd = open(file_path, O_CREAT | O_RDONLY | O_CLOEXEC, + variant->file_exec ? 00500 : 00400); + ASSERT_LE(0, fd); + EXPECT_EQ(0, close(fd)); + + /* Creates a test directory. */ + ASSERT_EQ(0, mkdir(dir_path, variant->file_exec ? 00500 : 00400)); + + /* Saves initial sysctl value. */ + self->initial_sysctl_value = sysctl_read_char(_metadata); + + /* Prepares for sysctl writes. */ + ignore_sys_admin(_metadata, 1); +} + +FIXTURE_TEARDOWN(omayexec) +{ + /* Restores initial sysctl value. */ + sysctl_write_char(_metadata, self->initial_sysctl_value); + + /* There is no need to unlink file_path nor dir_path. */ + ASSERT_EQ(0, umount(workdir_path)); + ASSERT_EQ(0, rmdir(workdir_path)); +} + +TEST_F(omayexec, sysctl_0) +{ + /* Do not enforce anything. */ + sysctl_write_char(_metadata, '0'); + test_dir_file(_metadata, 0); +} + +TEST_F(omayexec, sysctl_1) +{ + /* Enforces mount exec check. */ + sysctl_write_char(_metadata, '1'); + test_dir_file(_metadata, variant->sysctl_err_code[0]); +} + +TEST_F(omayexec, sysctl_2) +{ + /* Enforces file exec check. */ + sysctl_write_char(_metadata, '2'); + test_dir_file(_metadata, variant->sysctl_err_code[1]); +} + +TEST_F(omayexec, sysctl_3) +{ + /* Enforces mount and file exec check. */ + sysctl_write_char(_metadata, '3'); + test_dir_file(_metadata, variant->sysctl_err_code[2]); +} + +TEST(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 -- 2.27.0
