java缓冲区溢出编程心得

王朝java/jsp·作者佚名 2008-05-31

原创作者:sanool

前言:网上关于缓冲区溢出的资料也有很多,但我在阅读过程中发现介绍的都不是很明了,而且各网站也只是转贴老外的那篇译文而已,不仅内容有缺损,而且程序也无法调通,因为GCC版本不一样.经过几天的琢磨,终于明白了真正的原理,特地写出来分享.

测试环境:

$ gcc -v

Reading specs from /usr/lib/gcc-lib/i386-redhat-Linux/3.2.3/specs

Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --disable-checking --with-system-zlib --enable-__cxa_atexit --host=i386-redhat-linux

Thread model: posix

gcc version 3.2.3 20030502 (Red Hat Linux 3.2.3-24)

$ gdb -v

GNU gdb Red Hat Linux (6.0post-0.20031117.6rh)

GDB is free software, covered by the GNU General Public License, and you are

welcome to change it and/or distribute copies of it under certain conditions.

Type "show copying" to see the conditions.

There is absolutely no warranty for GDB. Type "show warranty" for details.

This GDB was configured as "i386-redhat-linux-gnu".

$ uname -a

Linux candy 2.4.21-9.EL #1 Thu Jan 8 17:03:13 EST 2004 i686 athlon i386 GNU/Linux

实例:

网上和我的这个实例雷同的也有,但是他们的是无法正确实现的.因为要害的跳转代码没有计算正确.(GCC版本问题,呵呵)

/************

* a.c

************/

void function(void)

{

char buffer[5];

int* ret;

ret=buffer+28;

(*ret)+=10;

}

void main()

{

int x;

x=0;

function();

x=1;

printf("%d\n",x);

return;

}

/*end*/

懂C语言的人都会认为最后的输出结果是1,可惜输出结果为0.为什么呢?请听解释.

实例分析:

相关堆栈的基础知识我就不罗嗦了,网上的介绍很多.

要害问题在于如何确定源代码

ret=buffer+28;

(*ret)+=10;

中的28 和 10

编译(会有warning,不用管他.)

$gcc -g -o a a.c //加上-g 用来在gdb中调试

$gdb a

(gdb)disas main //得到反汇编代码如下:

Dump of assembler code for function main:

0x08048366 <main+0>: push %ebp

0x08048367 <main+1>: mov %esp,%ebp

0x08048369 <main+3>: sub $0x8,%esp

0x0804836c <main+6>: and $0xfffffff0,%esp

0x0804836f <main+9>: mov $0x0,%eax

0x08048374 <main+14>: sub %eax,%esp

0x08048376 <main+16>: movl $0x0,0xfffffffc(%ebp)

0x0804837d <main+23>: call 0x8048348 <function>

0x08048382 <main+28>: movl $0x1,0xfffffffc(%ebp)

0x08048389 <main+35>: sub $0x8,%esp

0x0804838c <main+38>: pushl 0xfffffffc(%ebp)

0x0804838f <main+41>: push $0x8048474

0x08048394 <main+46>: call 0x8048288

0x08048399 <main+51>: add $0x10,%esp

0x0804839c <main+54>: leave

0x0804839d <main+55>: ret

End of assembler dump.

(gdb)disas function

Dump of assembler code for function function:

0x08048348 <