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ROP学习

EP 收录于 writeup
   约 3205 字   预计阅读 7 分钟 

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。

main程序

反汇编的结果如下图所示：
/images/2f353d576803642b0dfe02fd315664d3/11884068-b14b55b68c28b8e8.png

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:

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#!/usr/bin/env python    
    
import sys, os, binascii, time    
    
buf = (    
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"Uq0Uq1Uq2Uq3Uq4Uq5Uq6Uq7Uq8Uq9Ur0Ur1Ur2Ur3Ur4Ur5Ur6Ur7Ur8Ur9Us0Us1Us2Us3Us4Us5Us"    
"6Us7Us8Us9Ut0Ut1Ut2Ut3Ut4Ut5Ut6Ut7Ut8Ut9Uu0Uu1Uu2Uu3Uu4Uu5Uu6Uu7Uu8Uu9Uv0Uv1Uv2U"    
"v3Uv4Uv5Uv6Uv7Uv8Uv9Uw0Uw1Uw2Uw3Uw4Uw5Uw6Uw7Uw8Uw9Ux0Ux1Ux2Ux3Ux4Ux5Ux6Ux7Ux8Ux9"    
"Uy0Uy1Uy2Uy3Uy4Uy5Uy6Uy7Uy8Uy9Uz0Uz1Uz2Uz3Uz4Uz5Uz6Uz7Uz8Uz9Va0Va1Va2Va3Va4Va5Va"    
"6Va7Va8Va9Vb0Vb1Vb2Vb3Vb4Vb5Vb6Vb7Vb8Vb9Vc0Vc1Vc2Vc3Vc4Vc5Vc6Vc7Vc8Vc9Vd0Vd1Vd2V"    
"d3Vd4Vd5Vd6Vd7Vd8Vd9Ve0Ve1Ve2Ve3Ve4Ve5Ve6Ve7Ve8Ve9Vf0Vf1Vf2Vf3Vf4Vf5Vf6Vf7Vf8Vf9"    
"Vg0Vg1Vg2Vg3Vg4Vg5Vg6Vg7Vg8Vg9Vh0Vh1Vh2Vh3Vh4Vh5Vh6Vh7Vh8Vh9Vi0Vi1Vi2Vi3Vi4Vi5Vi"    
"6Vi7Vi8Vi9Vj0Vj1Vj2Vj3Vj4Vj5Vj6Vj7Vj8Vj9Vk0Vk1Vk2Vk3Vk4Vk5Vk6Vk7Vk8Vk9Vl0Vl1Vl2V"    
"l3Vl4Vl5Vl6Vl7Vl8Vl9Vm0Vm1Vm2Vm3Vm4Vm5Vm6Vm7Vm8Vm9Vn0Vn1Vn2Vn3Vn4Vn5Vn6Vn7Vn8Vn9"    
"Vo0Vo1Vo2Vo3Vo4Vo5Vo6Vo7Vo8Vo9Vp0Vp1Vp2Vp3Vp4Vp5Vp6Vp7Vp8Vp9Vq0Vq1Vq2Vq3Vq4Vq5Vq"    
"6Vq7Vq8Vq9Vr0Vr1Vr2Vr3Vr4Vr5Vr6Vr7Vr8Vr9Vs0Vs1Vs2Vs3Vs4Vs5Vs6Vs7Vs8Vs9Vt0Vt1Vt2V"    
"t3Vt4Vt5Vt6Vt7Vt8Vt9Vu0Vu1Vu2Vu3Vu4Vu5Vu6Vu7Vu8Vu9Vv0Vv1Vv2Vv3Vv4Vv5Vv6Vv7Vv8Vv9"    
"Vw0Vw1Vw2Vw3Vw4Vw5Vw6Vw7Vw8Vw9Vx0Vx1Vx2Vx3Vx4Vx5Vx6Vx7Vx8Vx9Vy0Vy1Vy2Vy3Vy4Vy5Vy"    
"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:

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$ 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:

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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。

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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:

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$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:
/images/2f353d576803642b0dfe02fd315664d3/11884068-f71c209c1f7c20dc.png

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:

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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
/images/2f353d576803642b0dfe02fd315664d3/11884068-9a28ae0a35834765.png

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}

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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}

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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

/images/2f353d576803642b0dfe02fd315664d3/11884068-93908b4f8a133afe.png

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。

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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:
/images/2f353d576803642b0dfe02fd315664d3/11884068-6b0add921b8d3549.png

x86-64的寄存器作用如图所示：
/images/2f353d576803642b0dfe02fd315664d3/11884068-bbc279bc2681ca84.png

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

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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'))

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

更新于 2020-04-05
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