栈随机化



为了防止入侵者通过缓冲区溢出进行攻击，linux系统实现了栈随机化技术。

如下代码用于打印出main函数局部变量的地址：

#include <stdio.h>

 

int main()

{

   int local;

   printf("local at %p\n", &local);

   sleep(-1);

   return0;

}

 

gcc -O1 -m32 -o stack_main stack_main.c

[root@bogon asm]# ./stack_main &

[1] 6129

[root@bogon asm]#local at 0xbffc2fa0

 

[root@bogon asm]# cat /proc/6129/maps

0046a000-005bd000 r-xp 00000000 08:02639384    /lib/libc-2.5.so

005bd000-005be000 --xp 00153000 08:02639384    /lib/libc-2.5.so

005be000-005c0000 r-xp 00153000 08:02639384    /lib/libc-2.5.so

005c0000-005c1000 rwxp 00155000 08:02639384    /lib/libc-2.5.so

005c1000-005c4000 rwxp 005c1000 00:00 0

008e3000-008e4000 r-xp 008e3000 00:000         [vdso]

00c8b000-00ca6000 r-xp 00000000 08:02639377    /lib/ld-2.5.so

00ca6000-00ca7000 r-xp 0001a000 08:02639377    /lib/ld-2.5.so

00ca7000-00ca8000 rwxp 0001b000 08:02639377    /lib/ld-2.5.so

08048000-08049000 r-xp 00000000 08:02 160831    /cspp/code-all/asm/stack_main

08049000-0804a000 rw-p 00000000 08:02160831    /cspp/code-all/asm/stack_main

b7f87000-b7f89000 rw-p b7f87000 00:00 0

b7f92000-b7f93000 rw-p b7f92000 00:00 0

bffaf000-bffc4000rw-p bffe9000 00:00 0         [stack]

 

[root@bogon asm]# ./stack_main &

[2] 6309

[root@bogon asm]#local at 0xbf912450

 

[root@bogon asm]# cat /proc/6309/maps

00110000-00263000 r-xp 00000000 08:02639384    /lib/libc-2.5.so

00263000-00264000 --xp 00153000 08:02639384    /lib/libc-2.5.so

00264000-00266000 r-xp 00153000 08:02639384    /lib/libc-2.5.so

00266000-00267000 rwxp 00155000 08:02639384    /lib/libc-2.5.so

00267000-0026a000 rwxp 00267000 00:00 0

00403000-00404000 r-xp 00403000 00:000         [vdso]

00728000-00743000 r-xp 00000000 08:02639377    /lib/ld-2.5.so

00743000-00744000 r-xp 0001a000 08:02639377    /lib/ld-2.5.so

00744000-00745000 rwxp 0001b000 08:02639377    /lib/ld-2.5.so

08048000-08049000 r-xp 00000000 08:02160831    /cspp/code-all/asm/stack_main

08049000-0804a000 rw-p 00000000 08:02160831    /cspp/code-all/asm/stack_main

b7f73000-b7f75000 rw-p b7f73000 00:00 0

b7f7e000-b7f7f000 rw-p b7f7e000 00:00 0

bf8fe000-bf913000rw-p bffe9000 00:00 0         [stack]

 

从中可以看到，局部变量的地址确实是在变化的，linux内核有开关可以查看和设置是否打开栈随机化功能。

对于我使用的red hatlinux5.8版本，关闭开关命令如下：

[root@bogon asm]# echo 0>/proc/sys/kernel/randomize_va_space

打开开关的命令：

[root@bogon asm]# echo 1>/proc/sys/kernel/randomize_va_space

 

关闭开关后：

[root@bogon asm]# ./stack_main &

[3] 6662

[root@bogon asm]#local at 0xbfffe850

[root@bogon asm]# cat /proc/6662/maps

00270000-00271000 r-xp 00270000 00:000         [vdso]

00290000-002ab000 r-xp 00000000 08:02639377    /lib/ld-2.5.so

002ab000-002ac000 r-xp 0001a000 08:02639377    /lib/ld-2.5.so

002ac000-002ad000 rwxp 0001b000 08:02639377    /lib/ld-2.5.so

00a66000-00bb9000 r-xp 00000000 08:02639384    /lib/libc-2.5.so

00bb9000-00bba000 --xp 00153000 08:02639384    /lib/libc-2.5.so

00bba000-00bbc000 r-xp 00153000 08:02639384    /lib/libc-2.5.so

00bbc000-00bbd000 rwxp 00155000 08:02639384    /lib/libc-2.5.so

00bbd000-00bc0000 rwxp 00bbd000 00:00 0

08048000-08049000 r-xp 00000000 08:02160831    /cspp/code-all/asm/stack_main

08049000-0804a000 rw-p 00000000 08:02160831    /cspp/code-all/asm/stack_main

b7ff4000-b7ff6000 rw-p b7ff4000 00:00 0

b7fff000-b8000000 rw-p b7fff000 00:00 0

bffea000-bffff000rw-p bffe9000 00:00 0         [stack]

 

[root@bogon asm]# ./stack_main &

[4] 6663

[root@bogon asm]#local at 0xbfffe850

[root@bogon asm]# cat /proc/6663/maps

006ca000-006cb000 r-xp 006ca000 00:000         [vdso]

00748000-0089b000 r-xp 00000000 08:02639384    /lib/libc-2.5.so

0089b000-0089c000 --xp 00153000 08:02639384    /lib/libc-2.5.so

0089c000-0089e000 r-xp 00153000 08:02639384    /lib/libc-2.5.so

0089e000-0089f000 rwxp 00155000 08:02639384    /lib/libc-2.5.so

0089f000-008a2000 rwxp 0089f000 00:00 0

00bab000-00bc6000 r-xp 00000000 08:02639377    /lib/ld-2.5.so

00bc6000-00bc7000 r-xp 0001a000 08:02639377    /lib/ld-2.5.so

00bc7000-00bc8000 rwxp 0001b000 08:02639377    /lib/ld-2.5.so

08048000-08049000 r-xp 00000000 08:02160831    /cspp/code-all/asm/stack_main

08049000-0804a000 rw-p 00000000 08:02160831    /cspp/code-all/asm/stack_main

b7ff4000-b7ff6000 rw-p b7ff4000 00:00 0

b7fff000-b8000000 rw-p b7fff000 00:00 0

bffea000-bffff000rw-p bffe9000 00:00 0         [stack]

 

局部变量在栈上分配的地址不再变化。