// SPDX-License-Identifier: GPL-2.0
#define _GNU_SOURCE
#include <stdio.h>
#include <errno.h>
#include <pwd.h>
#include <grp.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>
/*
* NOTES about this test:
* - requries libcap-dev to be installed on test system
* - requires securityfs to me mounted at /sys/kernel/security, e.g.:
* mount -n -t securityfs -o nodev,noexec,nosuid securityfs /sys/kernel/security
* - needs CONFIG_SECURITYFS and CONFIG_SAFESETID to be enabled
*/
#ifndef CLONE_NEWUSER
# define CLONE_NEWUSER 0x10000000
#endif
#define ROOT_UGID 0
#define RESTRICTED_PARENT_UGID 1
#define ALLOWED_CHILD1_UGID 2
#define ALLOWED_CHILD2_UGID 3
#define NO_POLICY_UGID 4
#define UGID_POLICY_STRING "1:2\n1:3\n2:2\n3:3\n"
char* add_uid_whitelist_policy_file = "/sys/kernel/security/safesetid/uid_allowlist_policy";
char* add_gid_whitelist_policy_file = "/sys/kernel/security/safesetid/gid_allowlist_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, "user %d", uid);
p.pw_name=name_str;
p.pw_uid=uid;
p.pw_gid=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_group_exists(gid_t gid)
{
struct group g;
FILE *fd;
char name_str[10];
if (getgrgid(gid) == NULL) {
memset(&g,0x00,sizeof(g));
fd=fopen("/etc/group","a");
if (fd == NULL)
die("couldn't open group file\n");
if (fseek(fd, 0, SEEK_END))
die("couldn't fseek group file\n");
snprintf(name_str, 10, "group %d", gid);
g.gr_name=name_str;
g.gr_gid=gid;
g.gr_passwd=NULL;
g.gr_mem=NULL;
int value = putgrent(&g,fd);
if (value != 0)
die("putgrent failed\n");
if (fclose(fd))
die("fclose failed\n");
}
}
static void ensure_securityfs_mounted(void)
{
int fd = open(add_uid_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_uid_whitelist_policy_file, strerror(errno));
}
}
}
static void write_uid_policies()
{
static char *policy_str = UGID_POLICY_STRING;
ssize_t written;
int fd;
fd = open(add_uid_whitelist_policy_file, O_WRONLY);
if (fd < 0)
die("can't open add_uid_whitelist_policy file\n");
written = write(fd, policy_str, strlen(policy_str));
if (written != strlen(policy_str)) {
if (written >= 0) {
die("short write to %s\n", add_uid_whitelist_policy_file);
} else {
die("write to %s failed: %s\n",
add_uid_whitelist_policy_file, strerror(errno));
}
}
if (close(fd) != 0) {
die("close of %s failed: %s\n",
add_uid_whitelist_policy_file, strerror(errno));
}
}
static void write_gid_policies()
{
static char *policy_str = UGID_POLICY_STRING;
ssize_t written;
int fd;
fd = open(add_gid_whitelist_policy_file, O_WRONLY);
if (fd < 0)
die("can't open add_gid_whitelist_policy file\n");
written = write(fd, policy_str, strlen(policy_str));
if (written != strlen(policy_str)) {
if (written >= 0) {
die("short write to %s\n", add_gid_whitelist_policy_file);
} else {
die("write to %s failed: %s\n",
add_gid_whitelist_policy_file, strerror(errno));
}
}
if (close(fd) != 0) {
die("close of %s failed: %s\n",
add_gid_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 %d 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 */
if (setuid(child_uid) < 0)
exit(EXIT_FAILURE);
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 test_setgid(gid_t child_gid, bool expect_success)
{
pid_t cpid, w;
int wstatus;
cpid = fork();
if (cpid == -1) {
die("fork\n");
}
if (cpid == 0) { /* Code executed by child */
if (setgid(child_gid) < 0)
exit(EXIT_FAILURE);
if (getgid() == child_gid)
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 test_setgroups(gid_t* child_groups, size_t len, bool expect_success)
{
pid_t cpid, w;
int wstatus;
gid_t groupset[len];
int i, j;
cpid = fork();
if (cpid == -1) {
die("fork\n");
}
if (cpid == 0) { /* Code executed by child */
if (setgroups(len, child_groups) != 0)
exit(EXIT_FAILURE);
if (getgroups(len, groupset) != len)
exit(EXIT_FAILURE);
for (i = 0; i < len; i++) {
for (j = 0; j < len; j++) {
if (child_groups[i] == groupset[j])
break;
if (j == len - 1)
exit(EXIT_FAILURE);
}
}
exit(EXIT_SUCCESS);
} 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_UGID);
ensure_user_exists(RESTRICTED_PARENT_UGID);
ensure_user_exists(ALLOWED_CHILD1_UGID);
ensure_user_exists(ALLOWED_CHILD2_UGID);
ensure_user_exists(NO_POLICY_UGID);
}
static void ensure_groups_exist(void)
{
ensure_group_exists(ROOT_UGID);
ensure_group_exists(RESTRICTED_PARENT_UGID);
ensure_group_exists(ALLOWED_CHILD1_UGID);
ensure_group_exists(ALLOWED_CHILD2_UGID);
ensure_group_exists(NO_POLICY_UGID);
}
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_groups_exist();
ensure_users_exist();
ensure_securityfs_mounted();
write_uid_policies();
write_gid_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 non-root
// user that doesn't have any restrictions (as long as it has
// CAP_SETUID);
if (setgid(NO_POLICY_UGID) < 0)
die("Error with set gid(%d)\n", NO_POLICY_UGID);
if (setuid(NO_POLICY_UGID) < 0)
die("Error with set uid(%d)\n", NO_POLICY_UGID);
// 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");
}
// Now switch to a user/group with restrictions
if (setgid(RESTRICTED_PARENT_UGID) < 0)
die("Error with set gid(%d)\n", RESTRICTED_PARENT_UGID);
if (setuid(RESTRICTED_PARENT_UGID) < 0)
die("Error with set uid(%d)\n", RESTRICTED_PARENT_UGID);
test_setuid(ROOT_UGID, false);
test_setuid(ALLOWED_CHILD1_UGID, true);
test_setuid(ALLOWED_CHILD2_UGID, true);
test_setuid(NO_POLICY_UGID, false);
test_setgid(ROOT_UGID, false);
test_setgid(ALLOWED_CHILD1_UGID, true);
test_setgid(ALLOWED_CHILD2_UGID, true);
test_setgid(NO_POLICY_UGID, false);
gid_t allowed_supp_groups[2] = {ALLOWED_CHILD1_UGID, ALLOWED_CHILD2_UGID};
gid_t disallowed_supp_groups[2] = {ROOT_UGID, NO_POLICY_UGID};
test_setgroups(allowed_supp_groups, 2, true);
test_setgroups(disallowed_supp_groups, 2, 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);
test_setgid(2, false);
test_setgid(3, false);
test_setgid(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.
printf("test successful!\n");
return EXIT_SUCCESS;
}
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