[原创]inctf-noodes-CTF对抗-看雪-安全社区|安全招聘|kanxue.com

[原创]inctf-noodes

发表于: 2021-8-18 18:22 9769

[原创]inctf-noodes

margina1

2021-8-18 18:22

9769

这个题算是诈胡出来的

参考链接:

https://linux.die.net/man/7/inotify

https://zh.wikipedia.org/wiki/Inotify

这个感觉和git有点点像, 监控文件的变动, 变动会生成事件

这里涉及的事件

这里4字节长度刚好对应index += ((_DWORD )byte + 3) + 16;的加16

除了2,3不能有名称之外都有2字节的名称

这里的字符串没有新建操作, 前面的文件初始化已经完成了(监控开启之前)

注意:df之后不能再打开文件, 否则会出现新建操作,(这里有一处就是这样df之后才mf的, 这里应该再df之前就打开, 我把这个操作放在了最前面, mf之前和cw之前一定要打开文件指针, 打开操作只需要一次, (mf, cw相同的文件只打开一次, 每次mf都会有cw收尾), exit会关闭所有的文件指针(这里也会被记录, 后打开的先关闭)

生成输入脚本: (因为mf操作不多, 我就直接手动删除多余的新建操作, 最后再加个8)

得到1hV4tT41B1HX25oQ6La6yQ4hV5jz55P325eh6GU5IZ4tN1AJ326Ti4XN5bX4wt6HW5ae5Fg4S11eP263U4Zv5gG16f25aq4Q94fz6Wy4I51l324dj1Pf326uM4bp61Q4Et6Cu4cj6fU4mV1mL21bl24hH6Qk5zr6Sm5VF49P1wV21xB326jg5Qc4fX4nZ6YO4CF1sF24Bp1vB21TR21Ax21gL26SI6Ye5q61BN25XE5Tn5Jt1Ah325Fr5t540x64i1Dz321Pz325gB5rl4f16yO5RN1Bl31Lx31Pd31JH311V3221Xt219321uj21Cx2221Xl21EZ221KP28

最后输入发现有错误, 调试之后发现, 从SafVR之后开始, 这里完全倒了过来,

要求的s1:mfFpmfP|mfThmfNLmf5ZcwFpcwP|cw\xcw=7cwyncwG|cwThcwNLcw\pcwI^cw5ZcwOT

生成的s1:mf5Zcw5ZmfNLcwNLcw\xcw=7cwyncwG|mfThcwThmfP|cwP|cw\pcwI^mfFpcwFpcwOT

具体调试了函数之后(前面有一个闹钟记得patch掉), 这里mf之后并没有把字符串写入, 是在fclose文件指针之后把文件修改, 那到底怎么连续修改之后再关闭文件指针呢, 这里我试了一下exit来关闭文件指针,把输入后面改成:

1hV4tT41B1HX25oQ6La6yQ4hV5jz55P325eh6GU5IZ4tN1AJ326Ti4XN5bX4wt6HW5ae5Fg4S11eP263U4Zv5gG16f25aq4Q94fz6Wy4I51l324dj1Pf326uM4bp61Q4Et6Cu4cj6fU4mV1mL21bl24hH6Qk5zr6Sm5VF49P1wV21xB326jg5Qc4fX4nZ6YO4CF1sF24Bp1vB21TR21Ax21gL26SI6Ye5q61BN25XE5Tn5Jt1Ah325Fr5t540x64i1Dz321Pz325gB5rl4f16yO5RN(这里开始修改)

1KP11V31EZ1Xl1JH31Pd31Cx1uj1931Xt1Lx31Bl38, 成功得到flag

if ( !strcmp(

          s1,

          "dfxXdf5FcwL\\adsUddPedd}UdflZafn~af9TmflZcwlZafilddKYafM^dfxRmfENcwENddXmdf\\Raff\\df{xddL[adeiadJkdfW5cwiTdd7"

          "Ydf^zadkKcw:jadeudfU=dfj~dd[}dfM9cwp7dfhnmfTjcwTjddyQdfftdd5UdfIxddGydfgnddjYdfqZcwqPcwfpdflLddUoaf~vddWqafZJd"

          "f=Tcw{Zmf|Fcw|FddnkadUgdfj\\dfr^dd]SdfGJcwwJdfFtcwzFcwXVcwE|cwkPddWMdd]iadu:cwFRad\\IafXrafNxmfElcwElafJvafx9d"

          "f4|dd8mmfH~cwH~mfT~cwT~afkFafvpdfj5dd}SafVRmfFpmfP|mfThmfNLmf5ZcwFpcwP|cw\\xcw=7cwyncwG|cwThcwNLcw\\pcwI^cw5ZcwOT") )

if ( !strcmp(

s1,

"dfxXdf5FcwL\\adsUddPedd}UdflZafn~af9TmflZcwlZafilddKYafM^dfxRmfENcwENddXmdf\\Raff\\df{xddL[adeiadJkdfW5cwiTdd7"

"Ydf^zadkKcw:jadeudfU=dfj~dd[}dfM9cwp7dfhnmfTjcwTjddyQdfftdd5UdfIxddGydfgnddjYdfqZcwqPcwfpdflLddUoaf~vddWqafZJd"

"f=Tcw{Zmf|Fcw|FddnkadUgdfj\\dfr^dd]SdfGJcwwJdfFtcwzFcwXVcwE|cwkPddWMdd]iadu:cwFRad\\IafXrafNxmfElcwElafJvafx9d"

"f4|dd8mmfH~cwH~mfT~cwT~afkFafvpdfj5dd}SafVRmfFpmfP|mfThmfNLmf5ZcwFpcwP|cw\\xcw=7cwyncwG|cwThcwNLcw\\pcwI^cw5ZcwOT") )

v45 = __readfsqword(0x28u);

  index = 0;

  s_index = 0;

  sub_55D31246E16A();

  sub_55D31246E1FA();

  fd = inotify_init();   //初始化一个 inotify 实例

  if ( fd < 0 )

    perror("inotify_init");

  sub_55D31246E4B7("/tmp/chall/"); //初始化文件

  wd = inotify_add_watch(fd, "/tmp/chall/", 0x33Fu); // 将监视添加到初始化的 inotify 实例

  pid = fork(); //新建进程

  if ( !pid )

    sub_55D31246E668("/tmp/chall/");   //用户输入处理,文件变动

  if ( waitpid(pid, &stat_loc, 0) == -1 )

  {

    perror("waitpid failed\n");

    goto LABEL_35;

  }

  v40 = BYTE1(stat_loc);

  printf("%d", BYTE1(stat_loc));

v45 = __readfsqword(0x28u);

index = 0;

s_index = 0;

sub_55D31246E16A();

sub_55D31246E1FA();

fd = inotify_init(); //初始化一个 inotify 实例

if ( fd < 0 )

perror("inotify_init");

sub_55D31246E4B7("/tmp/chall/"); //初始化文件

wd = inotify_add_watch(fd, "/tmp/chall/", 0x33Fu); // 将监视添加到初始化的 inotify 实例

pid = fork(); //新建进程

if ( !pid )

sub_55D31246E668("/tmp/chall/"); //用户输入处理,文件变动

if ( waitpid(pid, &stat_loc, 0) == -1 )

{

perror("waitpid failed\n");

goto LABEL_35;

}

v40 = BYTE1(stat_loc);

printf("%d", BYTE1(stat_loc));

size = read(fd, buf, 0x8000uLL);

  if ( size < 0 )

    perror("read");

  while ( index < size )

  {

    byte = &buf[index];

    if ( !*((_DWORD *)byte + 3) )

      goto LABEL_30;

    if ( (*((_DWORD *)byte + 1) & 0x100) != 0 ) // IN_CREATE 

    {

      v3 = s_index;

      if ( (*((_DWORD *)byte + 1) & 0x40000000) != 0 )// IN_ISDIR

      {

        ++s_index;

        s1[v3] = 'c';

        v4 = s_index++;

        s1[v4] = 'd';

      }

      else

      {

        ++s_index;

        s1[v3] = 'c';

        v5 = s_index++;

        s1[v5] = 'f';

      }
LABEL_26:

      v23 = byte[16] + 4;

      v24 = s_index++;

      s1[v24] = v23;

      v25 = byte[17] + 4;

      v26 = s_index++;

      s1[v26] = v25;

      goto LABEL_30;

    }

    if ( (*((_DWORD *)byte + 1) & 0x200) != 0 ) // IN_DELETE   

    {

      v6 = s_index;

      if ( (*((_DWORD *)byte + 1) & 0x40000000) != 0 )

      {

        ++s_index;

        s1[v6] = 'd';

        v7 = s_index++;

        s1[v7] = 'd';

      }

      else

      {

        ++s_index;

        s1[v6] = 'd';

        v8 = s_index++;

        s1[v8] = 'f';

      }

      goto LABEL_26;

    }

    if ( (*((_DWORD *)byte + 1) & 8) != 0 )     // IN_CLOSE_WRITE

    {

      v9 = s_index++;

      s1[v9] = 'c';

      v10 = s_index++;

      s1[v10] = 'w';

      v11 = byte[16] + 4;

      v12 = s_index++;

      s1[v12] = v11;

      v13 = byte[17] + 4;

      v14 = s_index++;

      s1[v14] = v13;

      goto LABEL_30;

    }

    if ( (*((_DWORD *)byte + 1) & 1) != 0 )     // IN_ACCESS

    {

      v15 = s_index++;

      s1[v15] = 'a';

      v16 = s_index++;

      s1[v16] = 'c';

      v17 = byte[16] + 4;

      v18 = s_index++;

      s1[v18] = v17;

      v19 = byte[17] + 4;

      v20 = s_index++;

      s1[v20] = v19;

      goto LABEL_30;

    }

    if ( (*((_DWORD *)byte + 1) & 4) != 0 )     // IN_ATTRIB 

    {

      v21 = s_index;

      if ( (*((_DWORD *)byte + 1) & 0x40000000) != 0 )

      {

        ++s_index;

        s1[v21] = 'a';

        v22 = s_index++;

        s1[v22] = 'd';

      }

      else

      {

        ++s_index;

        s1[v21] = 'a';

        v27 = s_index++;

        s1[v27] = 'f';

      }

      goto LABEL_26;

    }

    if ( (*((_DWORD *)byte + 1) & 2) != 0 )     // IN_MODIFY

    {

      v28 = s_index++;

      s1[v28] = 'm';

      v29 = s_index++;

      s1[v29] = 'f';

      v30 = byte[16] + 4;

      v31 = s_index++;

      s1[v31] = v30;

      v32 = byte[17] + 4;

      v33 = s_index++;

      s1[v33] = v32;

    }
LABEL_30:

    index += *((_DWORD *)byte + 3) + 16;

  }

size = read(fd, buf, 0x8000uLL);

if ( size < 0 )

perror("read");

while ( index < size )

{

byte = &buf[index];

if ( !*((_DWORD *)byte + 3) )

goto LABEL_30;

if ( (*((_DWORD *)byte + 1) & 0x100) != 0 ) // IN_CREATE

{

v3 = s_index;

if ( (*((_DWORD *)byte + 1) & 0x40000000) != 0 )// IN_ISDIR

{

++s_index;

s1[v3] = 'c';

v4 = s_index++;

s1[v4] = 'd';

}

else

{

++s_index;

s1[v3] = 'c';

v5 = s_index++;

s1[v5] = 'f';

}

LABEL_26:

v23 = byte[16] + 4;

v24 = s_index++;

s1[v24] = v23;

v25 = byte[17] + 4;

v26 = s_index++;

s1[v26] = v25;

goto LABEL_30;

}

if ( (*((_DWORD *)byte + 1) & 0x200) != 0 ) // IN_DELETE

{

v6 = s_index;

if ( (*((_DWORD *)byte + 1) & 0x40000000) != 0 )

{

++s_index;

s1[v6] = 'd';

v7 = s_index++;

s1[v7] = 'd';

}

else

{

++s_index;

s1[v6] = 'd';

v8 = s_index++;

s1[v8] = 'f';

}

goto LABEL_26;

}

if ( (*((_DWORD *)byte + 1) & 8) != 0 ) // IN_CLOSE_WRITE

{

v9 = s_index++;

s1[v9] = 'c';

v10 = s_index++;

s1[v10] = 'w';

v11 = byte[16] + 4;

v12 = s_index++;

s1[v12] = v11;

v13 = byte[17] + 4;

v14 = s_index++;

s1[v14] = v13;

goto LABEL_30;

}

if ( (*((_DWORD *)byte + 1) & 1) != 0 ) // IN_ACCESS

{

v15 = s_index++;

s1[v15] = 'a';

v16 = s_index++;

s1[v16] = 'c';

v17 = byte[16] + 4;

v18 = s_index++;

s1[v18] = v17;

v19 = byte[17] + 4;

v20 = s_index++;

s1[v20] = v19;

goto LABEL_30;

}

if ( (*((_DWORD *)byte + 1) & 4) != 0 ) // IN_ATTRIB

{

v21 = s_index;

if ( (*((_DWORD *)byte + 1) & 0x40000000) != 0 )

{

++s_index;

s1[v21] = 'a';

v22 = s_index++;

s1[v22] = 'd';

}

else

{

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[招生]科锐逆向工程师培训(2024年11月15日实地，远程教学同时开班, 第51期)

最后于 2021-8-18 23:39 被margina1编辑，原因：

#Reverse

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