new file mode 100644
@@ -0,0 +1 @@
+safesetid-test
new file mode 100644
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0
+# Makefile for mount selftests.
+CFLAGS = -Wall -lcap -O2
+
+TEST_PROGS := run_tests.sh
+TEST_GEN_FILES := safesetid-test
+
+include ../lib.mk
new file mode 100644
@@ -0,0 +1,2 @@
+CONFIG_SECURITY=y
+CONFIG_SECURITYFS=y
new file mode 100644
@@ -0,0 +1,334 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <errno.h>
+#include <pwd.h>
+#include <string.h>
+#include <syscall.h>
+#include <sys/capability.h>
+#include <sys/types.h>
+#include <sys/mount.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdarg.h>
+
+#ifndef CLONE_NEWUSER
+# define CLONE_NEWUSER 0x10000000
+#endif
+
+#define ROOT_USER 0
+#define RESTRICTED_PARENT 1
+#define ALLOWED_CHILD1 2
+#define ALLOWED_CHILD2 3
+#define NO_POLICY_USER 4
+
+char* add_whitelist_policy_file = "/sys/kernel/security/safesetid/add_whitelist_policy";
+
+static void die(char *fmt, ...)
+{
+ va_list ap;
+ va_start(ap, fmt);
+ vfprintf(stderr, fmt, ap);
+ va_end(ap);
+ exit(EXIT_FAILURE);
+}
+
+static bool vmaybe_write_file(bool enoent_ok, char *filename, char *fmt, va_list ap)
+{
+ char buf[4096];
+ int fd;
+ ssize_t written;
+ int buf_len;
+
+ buf_len = vsnprintf(buf, sizeof(buf), fmt, ap);
+ if (buf_len < 0) {
+ printf("vsnprintf failed: %s\n",
+ strerror(errno));
+ return false;
+ }
+ if (buf_len >= sizeof(buf)) {
+ printf("vsnprintf output truncated\n");
+ return false;
+ }
+
+ fd = open(filename, O_WRONLY);
+ if (fd < 0) {
+ if ((errno == ENOENT) && enoent_ok)
+ return true;
+ return false;
+ }
+ written = write(fd, buf, buf_len);
+ if (written != buf_len) {
+ if (written >= 0) {
+ printf("short write to %s\n", filename);
+ return false;
+ } else {
+ printf("write to %s failed: %s\n",
+ filename, strerror(errno));
+ return false;
+ }
+ }
+ if (close(fd) != 0) {
+ printf("close of %s failed: %s\n",
+ filename, strerror(errno));
+ return false;
+ }
+ return true;
+}
+
+static bool write_file(char *filename, char *fmt, ...)
+{
+ va_list ap;
+ bool ret;
+
+ va_start(ap, fmt);
+ ret = vmaybe_write_file(false, filename, fmt, ap);
+ va_end(ap);
+
+ return ret;
+}
+
+static void ensure_user_exists(uid_t uid)
+{
+ struct passwd p;
+
+ FILE *fd;
+ char name_str[10];
+
+ if (getpwuid(uid) == NULL) {
+ memset(&p,0x00,sizeof(p));
+ fd=fopen("/etc/passwd","a");
+ if (fd == NULL)
+ die("couldn't open file\n");
+ if (fseek(fd, 0, SEEK_END))
+ die("couldn't fseek\n");
+ snprintf(name_str, 10, "%d", uid);
+ p.pw_name=name_str;
+ p.pw_uid=uid;
+ p.pw_gecos="Test account";
+ p.pw_dir="/dev/null";
+ p.pw_shell="/bin/false";
+ int value = putpwent(&p,fd);
+ if (value != 0)
+ die("putpwent failed\n");
+ if (fclose(fd))
+ die("fclose failed\n");
+ }
+}
+
+static void ensure_securityfs_mounted(void)
+{
+ int fd = open(add_whitelist_policy_file, O_WRONLY);
+ if (fd < 0) {
+ if (errno == ENOENT) {
+ // Need to mount securityfs
+ if (mount("securityfs", "/sys/kernel/security",
+ "securityfs", 0, NULL) < 0)
+ die("mounting securityfs failed\n");
+ } else {
+ die("couldn't find securityfs for unknown reason\n");
+ }
+ } else {
+ if (close(fd) != 0) {
+ die("close of %s failed: %s\n",
+ add_whitelist_policy_file, strerror(errno));
+ }
+ }
+}
+
+static void write_policies(void)
+{
+ ssize_t written;
+ int fd;
+
+ fd = open(add_whitelist_policy_file, O_WRONLY);
+ if (fd < 0)
+ die("cant open add_whitelist_policy file\n");
+ written = write(fd, "1:2", strlen("1:2"));
+ if (written != strlen("1:2")) {
+ if (written >= 0) {
+ die("short write to %s\n", add_whitelist_policy_file);
+ } else {
+ die("write to %s failed: %s\n",
+ add_whitelist_policy_file, strerror(errno));
+ }
+ }
+ written = write(fd, "1:3", strlen("1:3"));
+ if (written != strlen("1:3")) {
+ if (written >= 0) {
+ die("short write to %s\n", add_whitelist_policy_file);
+ } else {
+ die("write to %s failed: %s\n",
+ add_whitelist_policy_file, strerror(errno));
+ }
+ }
+ if (close(fd) != 0) {
+ die("close of %s failed: %s\n",
+ add_whitelist_policy_file, strerror(errno));
+ }
+}
+
+static bool test_userns(bool expect_success)
+{
+ uid_t uid;
+ char map_file_name[32];
+ size_t sz = sizeof(map_file_name);
+ pid_t cpid;
+ bool success;
+
+ uid = getuid();
+
+ int clone_flags = CLONE_NEWUSER;
+ cpid = syscall(SYS_clone, clone_flags, NULL);
+ if (cpid == -1) {
+ printf("clone failed");
+ return false;
+ }
+
+ if (cpid == 0) { /* Code executed by child */
+ // Give parent 1 second to write map file
+ sleep(1);
+ exit(EXIT_SUCCESS);
+ } else { /* Code executed by parent */
+ if(snprintf(map_file_name, sz, "/proc/%d/uid_map", cpid) < 0) {
+ printf("preparing file name string failed");
+ return false;
+ }
+ success = write_file(map_file_name, "0 0 1", uid);
+ return success == expect_success;
+ }
+
+ printf("should not reach here");
+ return false;
+}
+
+static void test_setuid(uid_t child_uid, bool expect_success)
+{
+ pid_t cpid, w;
+ int wstatus;
+
+ cpid = fork();
+ if (cpid == -1) {
+ die("fork\n");
+ }
+
+ if (cpid == 0) { /* Code executed by child */
+ setuid(child_uid);
+ if (getuid() == child_uid)
+ exit(EXIT_SUCCESS);
+ else
+ exit(EXIT_FAILURE);
+ } else { /* Code executed by parent */
+ do {
+ w = waitpid(cpid, &wstatus, WUNTRACED | WCONTINUED);
+ if (w == -1) {
+ die("waitpid\n");
+ }
+
+ if (WIFEXITED(wstatus)) {
+ if (WEXITSTATUS(wstatus) == EXIT_SUCCESS) {
+ if (expect_success) {
+ return;
+ } else {
+ die("unexpected success\n");
+ }
+ } else {
+ if (expect_success) {
+ die("unexpected failure\n");
+ } else {
+ return;
+ }
+ }
+ } else if (WIFSIGNALED(wstatus)) {
+ if (WTERMSIG(wstatus) == 9) {
+ if (expect_success)
+ die("killed unexpectedly\n");
+ else
+ return;
+ } else {
+ die("unexpected signal: %d\n", wstatus);
+ }
+ } else {
+ die("unexpected status: %d\n", wstatus);
+ }
+ } while (!WIFEXITED(wstatus) && !WIFSIGNALED(wstatus));
+ }
+
+ die("should not reach here\n");
+}
+
+static void ensure_users_exist(void)
+{
+ ensure_user_exists(ROOT_USER);
+ ensure_user_exists(RESTRICTED_PARENT);
+ ensure_user_exists(ALLOWED_CHILD1);
+ ensure_user_exists(ALLOWED_CHILD2);
+ ensure_user_exists(NO_POLICY_USER);
+}
+
+static void drop_caps(bool setid_retained)
+{
+ cap_value_t cap_values[] = {CAP_SETUID, CAP_SETGID};
+ cap_t caps;
+
+ caps = cap_get_proc();
+ if (setid_retained)
+ cap_set_flag(caps, CAP_EFFECTIVE, 2, cap_values, CAP_SET);
+ else
+ cap_clear(caps);
+ cap_set_proc(caps);
+ cap_free(caps);
+}
+
+int main(int argc, char **argv)
+{
+ ensure_users_exist();
+ ensure_securityfs_mounted();
+ write_policies();
+
+ if (prctl(PR_SET_KEEPCAPS, 1L))
+ die("Error with set keepcaps\n");
+
+ // First test to make sure we can write userns mappings from a user
+ // that doesn't have any restrictions (as long as it has CAP_SETUID);
+ setuid(NO_POLICY_USER);
+ setgid(NO_POLICY_USER);
+
+ // Take away all but setid caps
+ drop_caps(true);
+
+ // Need PR_SET_DUMPABLE flag set so we can write /proc/[pid]/uid_map
+ // from non-root parent process.
+ if (prctl(PR_SET_DUMPABLE, 1, 0, 0, 0))
+ die("Error with set dumpable\n");
+
+ if (!test_userns(true)) {
+ die("test_userns failed when it should work\n");
+ }
+
+ setuid(RESTRICTED_PARENT);
+ setgid(RESTRICTED_PARENT);
+
+ test_setuid(ROOT_USER, false);
+ test_setuid(ALLOWED_CHILD1, true);
+ test_setuid(ALLOWED_CHILD2, true);
+ test_setuid(NO_POLICY_USER, false);
+
+ if (!test_userns(false)) {
+ die("test_userns worked when it should fail\n");
+ }
+
+ // Now take away all caps
+ drop_caps(false);
+ test_setuid(2, false);
+ test_setuid(3, false);
+ test_setuid(4, false);
+
+ // NOTE: this test doesn't clean up users that were created in
+ // /etc/passwd or flush policies that were added to the LSM.
+ return EXIT_SUCCESS;
+}
new file mode 100755
@@ -0,0 +1,26 @@
+#!/bin/bash
+
+TCID="safesetid-test.sh"
+errcode=0
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
+check_root()
+{
+ uid=$(id -u)
+ if [ $uid -ne 0 ]; then
+ echo $TCID: must be run as root >&2
+ exit $ksft_skip
+ fi
+}
+
+main_function()
+{
+ check_root
+ ./safesetid-test
+}
+
+main_function
+echo "$TCID: done"
+exit $errcode