TOC

Nullcon HackIM的第一道re题,虽然做出来了但是原理没太明白,flag里面显示用了ROP,所以学习一下。

参考链接

蒸米大佬的一步步学ROP系列

一步一步学ROP 之 Linux_x86篇
一步一步学ROP之linux_x64篇
一步一步学ROP之gadgets和2free篇

简洁版本

ROP技术入门教程

加一个z3的链接

z3 solver学习

main程序

反汇编的结果如下图所示:

程序存在溢出漏洞,使用蒸米大佬的脚本判断溢出长度。
脚本:

#!/usr/bin/env python  
  
import sys, os, binascii, time  
  
buf = (  
"Aa0Aa1Aa2Aa3Aa4Aa5Aa6Aa7Aa8Aa9Ab0Ab1Ab2Ab3Ab4Ab5Ab6Ab7Ab8Ab9Ac0Ac1Ac2Ac3Ac4Ac5Ac"  
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"6Vy7Vy8Vy9Vz0Vz1Vz2Vz3Vz4Vz5Vz6Vz7Vz8Vz9Wa0Wa1Wa2Wa3Wa4Wa5Wa6Wa7Wa8Wa9Wb0Wb1Wb2W"  
"b3Wb4Wb5Wb6Wb7Wb8Wb9Wc0Wc1Wc2Wc3Wc4Wc5Wc6Wc7Wc8Wc9Wd0Wd1Wd2Wd3Wd4Wd5Wd6Wd7Wd8Wd9"  
"We0We1We2We3We4We5We6We7We8We9Wf0Wf1Wf2Wf3Wf4Wf5Wf6Wf7Wf8Wf9Wg0Wg1Wg2Wg3Wg4Wg5Wg"  
"6Wg7Wg8Wg9Wh0Wh1Wh2Wh3Wh4Wh5Wh6Wh7Wh8Wh9Wi0Wi1Wi2Wi3Wi4Wi5Wi6Wi7Wi8Wi9Wj0Wj1Wj2W"  
"j3Wj4Wj5Wj6Wj7Wj8Wj9Wk0Wk1Wk2Wk3Wk4Wk5Wk6Wk7Wk8Wk9Wl0Wl1Wl2Wl3Wl4Wl5Wl6Wl7Wl8Wl9"  
"Wm0Wm1Wm2Wm3Wm4Wm5Wm6Wm7Wm8Wm9Wn0Wn1Wn2Wn3Wn4Wn5Wn6Wn7Wn8Wn9Wo0Wo1Wo2Wo3Wo4Wo5Wo"  
"6Wo7Wo8Wo9Wp0Wp1Wp2Wp3Wp4Wp5Wp6Wp7Wp8Wp9Wq0Wq1Wq2Wq3Wq4Wq5Wq6Wq7Wq8Wq9Wr0Wr1Wr2W"  
"r3Wr4Wr5Wr6Wr7Wr8Wr9Ws0Ws1Ws2Ws3Ws4Ws5Ws6Ws7Ws8Ws9Wt0Wt1Wt2Wt3Wt4Wt5Wt6Wt7Wt8Wt9"  
"Wu0Wu1Wu2Wu3Wu4Wu5Wu6Wu7Wu8Wu9Wv0Wv1Wv2Wv3Wv4Wv5Wv6Wv7Wv8Wv9Ww0Ww1Ww2Ww3Ww4Ww5Ww"  
"6Ww7Ww8Ww9Wx0Wx1Wx2Wx3Wx4Wx5Wx6Wx7Wx8Wx9Wy0Wy1Wy2Wy3Wy4Wy5Wy6Wy7Wy8Wy9Wz0Wz1Wz2W"  
"z3Wz4Wz5Wz6Wz7Wz8Wz9Xa0Xa1Xa2Xa3Xa4Xa5Xa6Xa7Xa8Xa9Xb0Xb1Xb2Xb3Xb4Xb5Xb6Xb7Xb8Xb9"  
"Xc0Xc1Xc2Xc3Xc4Xc5Xc6Xc7Xc8Xc9Xd0Xd1Xd2Xd3Xd4Xd5Xd6Xd7Xd8Xd9Xe0Xe1Xe2Xe3Xe4Xe5Xe"  
"6Xe7Xe8Xe9Xf0Xf1Xf2Xf3Xf4Xf5Xf6Xf7Xf8Xf9Xg0Xg1Xg2Xg3Xg4Xg5Xg6Xg7Xg8Xg9Xh0Xh1Xh2X"  
"h3Xh4Xh5Xh6Xh7Xh8Xh9Xi0Xi1Xi2Xi3Xi4Xi5Xi6Xi7Xi8Xi9Xj0Xj1Xj2Xj3Xj4Xj5Xj6Xj7Xj8Xj9"  
"Xk0Xk1Xk2Xk3Xk4Xk5Xk6Xk7Xk8Xk9Xl0Xl1Xl2Xl3Xl4Xl5Xl6Xl7Xl8Xl9Xm0Xm1Xm2Xm3Xm4Xm5Xm"  
"6Xm7Xm8Xm9Xn0Xn1Xn2Xn3Xn4Xn5Xn6Xn7Xn8Xn9Xo0Xo1Xo2Xo3Xo4Xo5Xo6Xo7Xo8Xo9Xp0Xp1Xp2X"  
"p3Xp4Xp5Xp6Xp7Xp8Xp9Xq0Xq1Xq2Xq3Xq4Xq5Xq6Xq7Xq8Xq9Xr0Xr1Xr2Xr3Xr4Xr5Xr6Xr7Xr8Xr9"  
"Xs0Xs1Xs2Xs3Xs4Xs5Xs6Xs7Xs8Xs9Xt0Xt1Xt2Xt3Xt4Xt5Xt6Xt7Xt8Xt9Xu0Xu1Xu2Xu3Xu4Xu5Xu"  
"6Xu7Xu8Xu9Xv0Xv1Xv2Xv3Xv4Xv5Xv6Xv7Xv8Xv9Xw0Xw1Xw2Xw3Xw4Xw5Xw6Xw7Xw8Xw9Xx0Xx1Xx2X"  
"x3Xx4Xx5Xx6Xx7Xx8Xx9Xy0Xy1Xy2Xy3Xy4Xy5Xy6Xy7Xy8Xy9Xz0Xz1Xz2Xz3Xz4Xz5Xz6Xz7Xz8Xz9"  
"Ya0Ya1Ya2Ya3Ya4Ya5Ya6Ya7Ya8Ya9Yb0Yb1Yb2Yb3Yb4Yb5Yb6Yb7Yb8Yb9Yc0Yc1Yc2Yc3Yc4Yc5Yc"  
"6Yc7Yc8Yc9Yd0Yd1Yd2Yd3Yd4Yd5Yd6Yd7Yd8Yd9Ye0Ye1Ye2Ye3Ye4Ye5Ye6Ye7Ye8Ye9Yf0Yf1Yf2Y"  
"f3Yf4Yf5Yf6Yf7Yf8Yf9Yg0Yg1Yg2Yg3Yg4Yg5Yg6Yg7Yg8Yg9Yh0Yh1Yh2Yh3Yh4Yh5Yh6Yh7Yh8Yh9"  
"Yi0Yi1Yi2Yi3Yi4Yi5Yi6Yi7Yi8Yi9Yj0Yj1Yj2Yj3Yj4Yj5Yj6Yj7Yj8Yj9Yk0Yk1Yk2Yk3Yk4Yk5Yk"  
"6Yk7Yk8Yk9Yl0Yl1Yl2Yl3Yl4Yl5Yl6Yl7Yl8Yl9Ym0Ym1Ym2Ym3Ym4Ym5Ym6Ym7Ym8Ym9Yn0Yn1Yn2Y"  
"n3Yn4Yn5Yn6Yn7Yn8Yn9Yo0Yo1Yo2Yo3Yo4Yo5Yo6Yo7Yo8Yo9Yp0Yp1Yp2Yp3Yp4Yp5Yp6Yp7Yp8Yp9"  
"Yq0Yq1Yq2Yq3Yq4Yq5Yq6Yq7Yq8Yq9Yr0Yr1Yr2Yr3Yr4Yr5Yr6Yr7Yr8Yr9Ys0Ys1Ys2Ys3Ys4Ys5Ys"  
"6Ys7Ys8Ys9Yt0Yt1Yt2Yt3Yt4Yt5Yt6Yt7Yt8Yt9Yu0Yu1Yu2Yu3Yu4Yu5Yu6Yu7Yu8Yu9Yv0Yv1Yv2Y"  
"v3Yv4Yv5Yv6Yv7Yv8Yv9Yw0Yw1Yw2Yw3Yw4Yw5Yw6Yw7Yw8Yw9Yx0Yx1Yx2Yx3Yx4Yx5Yx6Yx7Yx8Yx9"  
"Yy0Yy1Yy2Yy3Yy4Yy5Yy6Yy7Yy8Yy9Yz0Yz1Yz2Yz3Yz4Yz5Yz6Yz7Yz8Yz9Za0Za1Za2Za3Za4Za5Za"  
"6Za7Za8Za9Zb0Zb1Zb2Zb3Zb4Zb5Zb6Zb7Zb8Zb9Zc0Zc1Zc2Zc3Zc4Zc5Zc6Zc7Zc8Zc9Zd0Zd1Zd2Z"  
"d3Zd4Zd5Zd6Zd7Zd8Zd9Ze0Ze1Ze2Ze3Ze4Ze5Ze6Ze7Ze8Ze9Zf0Zf1Zf2Zf3Zf4Zf5Zf6Zf7Zf8Zf9"  
"Zg0Zg1Zg2Zg3Zg4Zg5Zg6Zg7Zg8Zg9Zh0Zh1Zh2Zh3Zh4Zh5Zh6Zh7Zh8Zh9Zi0Zi1Zi2Zi3Zi4Zi5Zi"  
"6Zi7Zi8Zi9Zj0Zj1Zj2Zj3Zj4Zj5Zj6Zj7Zj8Zj9Zk0Zk1Zk2Zk3Zk4Zk5Zk6Zk7Zk8Zk9Zl0Zl1Zl2Z"  
"l3Zl4Zl5Zl6Zl7Zl8Zl9Zm0Zm1Zm2Zm3Zm4Zm5Zm6Zm7Zm8Zm9Zn0Zn1Zn2Zn3Zn4Zn5Zn6Zn7Zn8Zn9"  
"Zo0Zo1Zo2Zo3Zo4Zo5Zo6Zo7Zo8Zo9Zp0Zp1Zp2Zp3Zp4Zp5Zp6Zp7Zp8Zp9Zq0Zq1Zq2Zq3Zq4Zq5Zq"  
"6Zq7Zq8Zq9Zr0Zr1Zr2Zr3Zr4Zr5Zr6Zr7Zr8Zr9Zs0Zs1Zs2Zs3Zs4Zs5Zs6Zs7Zs8Zs9Zt0Zt1Zt2Z"  
"t3Zt4Zt5Zt6Zt7Zt8Zt9Zu0Zu1Zu2Zu3Zu4Zu5Zu6Zu7Zu8Zu9Zv0Zv1Zv2Zv3Zv4Zv5Zv6Zv7Zv8Zv9"  
"Zw0Zw1Zw2Zw3Zw4Zw5Zw6Zw7Zw8Zw9Zx0Zx1Zx2Zx3Zx4Zx5Zx6Zx7Zx8Zx9Zy0Zy1Zy2Zy3Zy4Zy5Zy"  
"6Zy7Zy8Zy9Zz0Zz1Zz2Zz3Zz4Zz5Zz6Zz7Zz8Zz9"  
)  
  
def show_error(msg):  
	sys.stderr.write(os.linesep * 2 + "ERROR: " + msg + os.linesep * 3)  
	sys.exit(1)  
  
def bare_words():  
	string = " ".join(sys.argv[1:])  
	print "The used string: =>" + string + "<="  
	return string  
  
  
def show_help():  
	print sys.argv[0] + " create <int>"  
	print "\tReturns a pattern of <int> chars."  
	print  
	print sys.argv[0] + " offset <str> [size <int>]"  
	print (  
		"\tReturns the offset for the provided argument <str>. Must be at least "  
		"three chars for non ambiguous match. May be a hex value. The conversion"  
		"is done automatically for little endian architectures (ie: x86). This "  
		"basically means that the string obtained from hex conversion is "  
		"reversed. WARNING: The hex decoding is skipped for valid hex values "  
		"that are part of the buffer itself as the hex decoding is a fallback "  
		"measure. Always use the 0x prefix in order to force the hex decoding."  
		"" + os.linesep + ""  
		"\tFor patterns longer than 20280 chars you must provide the optional "  
		"argument size in order to receive all the offsets for the Aa0 pattern."  
	)  
	sys.exit(0)  
  
def show_pattern(size):  
	size = int(size)  
	count = size // 20280  
	inc = 0  
	while inc < count:  
		sys.stdout.write(buf)  
		inc += 1  
	  
	mod = size % 20280  
	sys.stdout.write(buf[:mod])  
	print  
	  
def decode_offset(offset):  
	offset = offset.replace("0x", "")  
	try:  
		offset = binascii.unhexlify(offset)  
		offset = offset[::-1]  
		print "hex pattern decoded as: " + offset  
		return offset  
	except TypeError:  
		sploit.show_error("Invalid input offset.")  
  
def show_offset(offset, size):  
	try:  
		pos = buf.index(offset)  
		if size == 0:  
			print pos  
		else:  
			position = list()  
			count = size // 20280  
			inc = 0  
			while inc < count:  
				position.append(str(inc * 20280 + pos))  
				inc += 1  
			  
			mod = size % 20280  
			if pos + len(offset) <= mod:  
				position.append(str(inc * 20280 + pos))  
			  
			print os.linesep.join(position)  
	except ValueError:  
		offset = decode_offset(offset)  
		show_offset(offset, size)  
  
if __name__ == "__main__":  
	if len(sys.argv) == 1:  
		show_help()  
	elif sys.argv[1] != "create" and sys.argv[1] != "offset":  
		show_help()  
	  
	try:  
		try:  
			if sys.argv[1] == "create" and sys.argv[2].isdigit():  
				show_pattern(sys.argv[2])  
		except IndexError:  
			sploit.show_error("You need to supply the <int> value for the create action.")  
		  
		try:  
			if sys.argv[1] == "offset" and sys.argv[2]:  
				try:  
					size = int(sys.argv[3])  
				except IndexError:  
					size = 0  
				  
				show_offset(sys.argv[2], size)  
		except IndexError:  
			sploit.show_error("You need to supply the <str> value for the offset action.")  
	except KeyboardInterrupt:  
		sploit.show_error("Keyboard interrupt received. Educated guess: the script took too long to execute. You used a really long size, didn't you?")  

首先生成长度为150的字符串:

$ python pattern.py create 150  
Aa0Aa1Aa2Aa3Aa4Aa5Aa6Aa7Aa8Aa9Ab0Ab1Ab2Ab3Ab4Ab5Ab6Ab7Ab8Ab9Ac0Ac1Ac2Ac3Ac4Ac5Ac6Ac7Ac8Ac9Ad0Ad1Ad2Ad3Ad4Ad5Ad6Ad7Ad8Ad9Ae0Ae1Ae2Ae3Ae4Ae5Ae6Ae7Ae8Ae9  

用gdb打开main文件,输入生成的长度为150的字符串:

gdb-peda$ run  
Starting program: /home/ep/Desktop/main   
Hello world!  
Aa0Aa1Aa2Aa3Aa4Aa5Aa6Aa7Aa8Aa9Ab0Ab1Ab2Ab3Ab4Ab5Ab6Ab7Ab8Ab9Ac0Ac1Ac2Ac3Ac4Ac5Ac6Ac7Ac8Ac9Ad0Ad1Ad2Ad3Ad4Ad5Ad6Ad7Ad8Ad9Ae0Ae1Ae2Ae3Ae4Ae5Ae6Ae7Ae8Ae9  
  
Program received signal SIGSEGV, Segmentation fault.  
......  
[------------------------------------------------------------------------------]  
Legend: code, data, rodata, value  
Stopped reason: SIGSEGV  
0x00000000004012a6 in ?? ()  

64位程序使用的内存地址不能大于0x00007fffffffffff,否则会抛出异常。但是,虽然PC不能跳转到那个地址,我们依然可以通过栈来计算出溢出点。因为ret相当于“pop rip”指令,所以我们只要看一下栈顶的数值就能知道PC跳转的地址了。

gdb-peda$ x/gx $rsp  
0x7fffffffdf88:	0x4130634139624138  

得出溢出点存在于0x4130634139624138处。再次使用蒸米大佬的脚本:

$python pattern.py offset 0x4130634139624138  
hex pattern decoded as: 8Ab9Ac0A  
56  

故溢出长度为56,一般: payload = “a” * 56 + ret_addr
给出的blob文件如下:

可以看到给出的字符串a长度就是56,后面0x4011A2是返回地址,0x4040A0是存储flag字符串dest的地址。这个blob文件相当于一个大型gadgets,可以进行一系列操作随后将值写入EAX并返回。
可以使用如下命令在gdb中尝试调试:

python -c 'print "\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\xA2\x11\x40\x00\x00\x00\x00\x00\xA0\x40\x40\x00\x00\x00\x00\x00\x9A\x11\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xA4\x11\x40\x00\x00\x00\x00\x00\xEA\x11\x40\x00\x00\x00\x00\x00\xD6\x11\x40\x00\x00\x00\x00\x00\xA2\x11\x40\x00\x00\x00\x00\x00\xA0\x40\x40\x00\x00\x00\x00\x00\x9C\x11\x40\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\xA8\x11\x40\x00\x00\x00\x00\x00\xEE\x11\x40\x00\x00\x00\x00\x00\xDB\x11\x40\x00\x00\x00\x00\x00\xA2\x11\x40\x00\x00\x00\x00\x00\xA0\x40\x40\x00\x00\x00\x00\x00\x9E\x11\x40\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\xAC\x11\x40\x00\x00\x00\x00\x00\xF2\x11\x40\x00\x00\x00\x00\x00\xE0\x11\x40\x00\x00\x00\x00\x00\xBD\x11\x40\x00\x00\x00\x00\x00\xA4\x11\x40\x00\x00\x00\x00\x00\xA8\x11\x40\x00\x00\x00\x00\x00\xAC\x11\x40\x00\x00\x00\x00\x00\x9A\x11\x40\x00\x00\x00\x00\x00\x64\x00\x00\x00\x00\x00\x00\x00\xC1\x11\x40\x00\x00\x00\x00\x00\xEA\x11\x40\x00\x00\x00\x00\x00\xFF\x11\x40\x00\x00\x00\x00\x00"' > payload  
  
gdb-peda$ b * 0x401226  
Breakpoint 1 at 0x401226  
gdb-peda$ run < payload  

如下图是我进行调试的一个片段

解题

从上面的解析可以看出,最后的返回值就是把flag进行一系列线性变换得到的,所以需要首先得到具体的线性变换,然后使用z3求解器进行求解。
下面的脚本用于求线性变换, 其中flag文件中填入的字符串为: hackim20{00000000000000000000000}

import subprocess  
  
o = [296, 272, 272, 272, 296, 360, 272, 424, 272, 208, 120, 120, 120, 96, 120, 120, 120, 120, 120, 120, 120, 208, 120, 120, 208, 208, 208, 208, 208, 272, 120, 208, 208]  
  
r = [208, 225, 237, 20, 214, 183, 79, 105, 207, 217, 125, 66, 123, 104, 97, 99, 107 , 105, 109, 50, 48, 202, 111, 111, 29, 63, 223, 36, 0, 124, 100, 219, 32]  
  
cmd = ['./main']  
  
def getret():  
	rets = []  
	with open('blob', 'rb') as f:  
		for offset in o:  
			data = f.read(offset)  
			p = subprocess.Popen(cmd, stdin=subprocess.PIPE)  
			p.stdin.write(data)  
			p.communicate()  
			rets.append(p.returncode)  
	return rets  
  
if __name__ == "__main__":  
	r = getret()  
	dic = {}  
	
	for i in range(24):  
		flag = "hackim20{" + "0" * i + "1" + "0" * (23 - i) + "}"  
		with open('flag', 'w') as f:  
			f.write(flag)  
		ret = getret()  
		for j in range(len(ret)):  
			if ret[j] != r[j]:  
				if not dic.has_key(j):  
					dic[j] = {}  
				dic[j][i] = ret[j] - r[j]  
	print dic  

最后打印的dic中是flag中哪些字符串能够影响第i个输出的returncode.
下面的脚本用于使用z3的求解, 其中flag文件中填入的字符串依然是: hackim20{00000000000000000000000}

import subprocess  
from z3 import *  
  
o = [296, 272, 272, 272, 296, 360, 272, 424, 272, 208, 120, 120, 120, 96, 120, 120, 120, 120, 120, 120, 120, 208, 120, 120, 208, 208, 208, 208, 208, 272, 120, 208, 208]  
  
r = [208, 225, 237, 20, 214, 183, 79, 105, 207, 217, 125, 66, 123, 104, 97, 99, 107 , 105, 109, 50, 48, 202, 111, 111, 29, 63, 223, 36, 0, 124, 100, 219, 32]  
  
cmd = ['./main']  
  
def getret():  
	rets = []  
	with open('blob', 'rb') as f:  
		for offset in o:  
			data = f.read(offset)  
			p = subprocess.Popen(cmd, stdin=subprocess.PIPE)  
			p.stdin.write(data)  
			p.communicate()  
			rets.append(p.returncode)  
	return rets  
  
if __name__ == "__main__":  
	ret = getret()  
	dic = {1: {1: 1}, 2: {3: 1, 5: 1, 7: 1}, 3: {9: 1, 21: -1}, 4: {13: 1}, 5: {19: 1, 20: 1}, 6: {0: 1, 8: 1, 2: -1}, 7: {10: -1, 11: 1, 4: 1, 18: -1, 6: 1}, 8: {12: 1, 14: 2}, 9: {16: 1, 17: 1}, 10: {21: 1}, 11: {0: 1}, 21: {2: 1}, 22: {20: 1}, 23: {20: 1}, 24: {20: 1, 4: -1}, 25: {19: 1, 5: -1}, 26: {19: 1, 6: 1}, 27: {18: -1}, 28: {14: 1, 15: -1}, 29: {17: 1}, 30: {10: 1}, 31: {2: 1, 3: 1}, 32: {11: -1, 12: 1}}  
	solver = Solver()  
	val = [Int('x%i' % i) for i in range(23)]  
	for i in range(23):  
		solver.add(val[i] > 20)  
		solver.add(val[i] < 0x7f)  
	for i in range(33):  
		if dic.has_key(i):  
			keys = dic[i].keys()  
			a = r[i] - ret[i]  
			b = 0  
			for k in keys:  
				b = b + (val[k] - ord('0')) * dic[i][k]  
			solver.add(a == b)  
	# print solver  
	print solver.check()  
	answer=solver.model()  
	print answer  
	tidy_answer="".join([chr(answer[each].as_long()) for each in val])  
	print "hackim20{" + tidy_answer  

hackim20{B4byR0pDo0dOod00duDoo}

官方解法

blob是一个大型的ROP文件,所以本质是一个虚拟机,对输入的字符串进行一系列操作后,根据return输出。

import struct  
  
o = [296, 272, 272, 272, 296, 360, 272, 424, 272, 208, 120, 120, 120, 96, 120, 120, 120, 120, 120, 120, 120, 208, 120, 120, 208, 208, 208, 208, 208, 272, 120, 208, 208]  
r = [208, 225, 237, 20, 214, 183, 79, 105, 207, 217, 125, 66, 123, 104, 97, 99, 107 , 105, 109, 50, 48, 202, 111, 111, 29, 63, 223, 36, 0, 124, 100, 219, 32]  
  
bufs = []  
gadgets = set()  
  
with open('blob', 'rb') as f:  
	for offset in o:  
		data = f.read(offset)  
		bufs.append(data)  
  
def decode(buf):  
	na = 56  
	data_l = []  
	data = None  
	for i in range(na, len(buf), 8):  
		data = buf[i:i+8]  
		print data  
		data = struct.unpack('<Q', data)[0] #unpack成8字节的小端序数据  
		print data  
		data_l.append(data)  
		if data > 0x400000:  
			gadgets.add(data)  
	return data_l  
  
# for buf in bufs:  
#     addrs = decode(buf)  
# for g in gadgets:  
#     print(hex(g)[2:])  
# for i in `python solution.py`; do echo $i; objdump -d ../dist/main -j.text -M intel | grep $i; echo "--------------------"; done  
  
dis = {}  
dis[0x40119a] = 'pop rdi'  
dis[0x40119c] = 'pop rsi'  
dis[0x40119e] = 'pop rdx'  
  
'''  
 23 .bss          00000048  0000000000404080  0000000000404080  00003068  2**5  
              ALLOC  
'''  
dis[0x4040a0] = 'flag'  
dis[0x4011a0] = 'pop rcx'  
dis[0x4011a2] = 'pop rax'  
dis[0x4011a4] = 'add rax, rdi'  
dis[0x4011a8] = 'add rax, rsi'  
dis[0x4011ac] = 'add rax, rdx'  
dis[0x4011b0] = 'add rax, rcx'  
dis[0x4011bd] = 'xor rax, rax'  
dis[0x4011c1] = 'sub rax, rdi'  
dis[0x4011c5] = 'sub rqx, rsi'  
dis[0x4011c9] = 'sub rax, rdx'  
dis[0x4011cd] = 'sub rax, rcx'  
dis[0x4011d6] = 'movzx rdi, BYTE PTR [rdi]'  
dis[0x4011db] = 'movzx rsi, BYTE PTR [rsi]'  
dis[0x4011e0] = 'movzx rdx, BYTE PTR [rdx]'  
dis[0x4011e5] = 'movzd rcx, BYTE PTR [rcx]'  
dis[0x4011ea] = 'mov rdi, rax'  
dis[0x4011ee] = 'mov rsi, rax'  
dis[0x4011f2] = 'mov rdx, rax'  
dis[0x4011f6] = 'mov rcx, rax'  
dis[0x4011ff] = 'call exit@plt'  
  
for buf in bufs:  
	addrs = decode(buf)  
	for addr in addrs:  
		try:  
			print(dis[addr])  
		except KeyError:  
			print(hex(addr))  
  
print('---------------------------')  

翻译出来的字节码如下:

x86-64的寄存器作用如图所示:

rdi寄存器中是exit函数的参数,所以最后的返回值就是rdi中的值。
根据以上操作使用z3解题

from z3 import *  
  
s = Solver()  
n = 31  
  
bv = []  
for i in range(n):  
	bv.append(BitVec('bv_{}'.format(i), 32))  
  
alphabet = b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789{}'  
  
for i in range(n):  
	s.add(bv[i] >= min(alphabet))  
	s.add(bv[i] <= max(alphabet))  
	
	s.add(bv[0] + bv[2] + bv[4] - 100 == 208)  
	s.add(bv[6] + bv[8] + bv[10] == 225)  
	s.add(bv[12] + bv[14] + bv[16] == 237)  
	s.add(bv[18] + bv[1] - bv[30] == 20)  
	s.add(bv[3] + bv[22] + bv[3] - 100 == 214)  
	s.add(bv[5] + bv[29] + bv[28] - bv[7] - 100 == 183)  
	s.add(bv[9] + bv[17] - bv[11] == 79)  
	s.add(bv[13] + bv[15] - bv[19] + bv[20] - bv[27] == 105)  
	s.add(bv[21] + bv[23] + bv[24] == 207)  
	s.add(bv[25] + bv[26] == 217)  
	s.add(bv[30] == 125)  
	s.add(bv[9] == 66)  
	s.add(bv[8] == 123)  
	s.add(bv[0] == 104)  
	s.add(bv[1] == 97)  
	s.add(bv[2] == 99)  
	s.add(bv[3] == 107)  
	s.add(bv[4] == 105)  
	s.add(bv[5] == 109)  
	s.add(bv[6] == 50)  
	s.add(bv[7] == 48)  
	s.add(bv[11] + bv[0] == 202)  
	s.add(bv[29] == 111)  
	s.add(bv[28] == 111)  
	s.add(bv[29] - bv[13] == 29)  
	s.add(bv[28] - bv[14] == 63)  
	s.add(bv[28] + bv[15] == 223)  
	s.add(bv[0] - bv[27] == 36)  
	s.add(bv[23] - bv[24] == 0)  
	s.add(bv[26] + bv[0] - bv[1] == 124)  
	s.add(bv[19] == 100)  
	s.add(bv[11] + bv[12] == 219)  
	s.add(bv[21] - bv[20] == 32)  
  
s.check()  
m = s.model()  
ans = bytearray()  
  
for i in range(n):  
c = m[bv[i]].as_long()  
ans.append(c)  
  
print(ans.decode('utf-8'))