2017-08-05 19:44:45 +07:00
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# Linux 命令行技巧
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- [重定向输入字符](#重定向输入字符)
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2017-08-06 13:52:07 +07:00
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- [从可执行文件中提取 shellcode](#从可执行文件中提取-shellcode)
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- [查看进程虚拟地址空间](#查看进程虚拟地址空间)
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2017-08-10 22:25:09 +07:00
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- [ASCII 表](#ascii-表)
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2017-08-05 19:44:45 +07:00
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## 重定向输入字符
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有时候我们需要在 shell 里输入键盘上没有对应的字符，如 `0x1F`，就需要使用重定向输入。下面是一个例子：[源码](../src/Others/4.2_0x1f.c)
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2017-08-06 13:52:07 +07:00
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## 从可执行文件中提取 shellcode
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```text
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for i in `objdump -d print_flag | tr '\t' ' ' | tr ' ' '\n' | egrep '^[0-9a-f]{2}$' ` ; do echo -n "\x$i" ; done
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```
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注意：在 objdump 中空字节可能会被删除。
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## 查看进程虚拟地址空间
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有时我们需要知道一个进程的虚拟地址空间是如何使用的，以确定栈是否是可执行的。
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```text
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$ cat /proc/<PID>/maps
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```
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下面我们分别来看看可执行栈和不可执行栈的不同：
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```text
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$ cat hello.c
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#include <stdio.h>
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void main()
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{
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char buf[128];
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scanf("hello, world: %s\n", buf);
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}
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$ gcc hello.c -o a.out1
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$ ./a.out1 &
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[1] 7403
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$ cat /proc/7403/maps
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555555554000-555555555000 r-xp 00000000 08:01 26389924 /home/firmy/a.out1
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555555754000-555555755000 r--p 00000000 08:01 26389924 /home/firmy/a.out1
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555555755000-555555756000 rw-p 00001000 08:01 26389924 /home/firmy/a.out1
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555555756000-555555777000 rw-p 00000000 00:00 0 [heap]
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7ffff7a33000-7ffff7bd0000 r-xp 00000000 08:01 21372436 /usr/lib/libc-2.25.so
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7ffff7bd0000-7ffff7dcf000 ---p 0019d000 08:01 21372436 /usr/lib/libc-2.25.so
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7ffff7dcf000-7ffff7dd3000 r--p 0019c000 08:01 21372436 /usr/lib/libc-2.25.so
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7ffff7dd3000-7ffff7dd5000 rw-p 001a0000 08:01 21372436 /usr/lib/libc-2.25.so
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7ffff7dd5000-7ffff7dd9000 rw-p 00000000 00:00 0
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7ffff7dd9000-7ffff7dfc000 r-xp 00000000 08:01 21372338 /usr/lib/ld-2.25.so
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7ffff7fbc000-7ffff7fbe000 rw-p 00000000 00:00 0
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7ffff7ff8000-7ffff7ffa000 r--p 00000000 00:00 0 [vvar]
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7ffff7ffa000-7ffff7ffc000 r-xp 00000000 00:00 0 [vdso]
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7ffff7ffc000-7ffff7ffd000 r--p 00023000 08:01 21372338 /usr/lib/ld-2.25.so
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7ffff7ffd000-7ffff7ffe000 rw-p 00024000 08:01 21372338 /usr/lib/ld-2.25.so
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7ffff7ffe000-7ffff7fff000 rw-p 00000000 00:00 0
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7ffffffde000-7ffffffff000 rw-p 00000000 00:00 0 [stack]
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ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
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[1]+ Stopped ./a.out1
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$ gcc -z execstack hello.c -o a.out2
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$ ./a.out2 &
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[2] 7467
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[firmy@manjaro ~]$ cat /proc/7467/maps
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555555554000-555555555000 r-xp 00000000 08:01 26366643 /home/firmy/a.out2
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555555754000-555555755000 r-xp 00000000 08:01 26366643 /home/firmy/a.out2
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555555755000-555555756000 rwxp 00001000 08:01 26366643 /home/firmy/a.out2
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555555756000-555555777000 rwxp 00000000 00:00 0 [heap]
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7ffff7a33000-7ffff7bd0000 r-xp 00000000 08:01 21372436 /usr/lib/libc-2.25.so
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7ffff7bd0000-7ffff7dcf000 ---p 0019d000 08:01 21372436 /usr/lib/libc-2.25.so
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7ffff7dcf000-7ffff7dd3000 r-xp 0019c000 08:01 21372436 /usr/lib/libc-2.25.so
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7ffff7dd3000-7ffff7dd5000 rwxp 001a0000 08:01 21372436 /usr/lib/libc-2.25.so
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7ffff7dd5000-7ffff7dd9000 rwxp 00000000 00:00 0
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7ffff7dd9000-7ffff7dfc000 r-xp 00000000 08:01 21372338 /usr/lib/ld-2.25.so
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7ffff7fbc000-7ffff7fbe000 rwxp 00000000 00:00 0
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7ffff7ff8000-7ffff7ffa000 r--p 00000000 00:00 0 [vvar]
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7ffff7ffa000-7ffff7ffc000 r-xp 00000000 00:00 0 [vdso]
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7ffff7ffc000-7ffff7ffd000 r-xp 00023000 08:01 21372338 /usr/lib/ld-2.25.so
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7ffff7ffd000-7ffff7ffe000 rwxp 00024000 08:01 21372338 /usr/lib/ld-2.25.so
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7ffff7ffe000-7ffff7fff000 rwxp 00000000 00:00 0
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7ffffffde000-7ffffffff000 rwxp 00000000 00:00 0 [stack]
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ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
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[2]+ Stopped ./a.out2
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```
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当使用 `-z execstack` 参数进行编译时，会关闭 `Stack Protector`。我们可以看到在 `a.out1` 中的 `stack` 是 `rw` 的，而 `a.out2` 中则是 `rwx` 的。
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`maps` 文件有 6 列，分别为：
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- **地址**：库在进程里地址范围
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- **权限**：虚拟内存的权限，r=读，w=写,x=执行,s=共享,p=私有
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- **偏移量**：库在进程里地址偏移量
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- **设备**：映像文件的主设备号和次设备号，可以通过通过 `cat /proc/devices` 查看设备号对应的设备名
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- **节点**：映像文件的节点号
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- **路径**: 映像文件的路径，经常同一个地址有两个地址范围，那是因为一段是 `r-xp` 为只读的代码段，一段是 `rwxp` 为可读写的数据段
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2017-08-10 22:25:09 +07:00
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## ASCII 表
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ASCII 表将键盘上的所有字符映射到固定的数字。有时候我们可能需要查看这张表：
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```text
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$ man ascii
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Oct Dec Hex Char Oct Dec Hex Char
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────────────────────────────────────────────────────────────────────────
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000 0 00 NUL '\0' (null character) 100 64 40 @
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001 1 01 SOH (start of heading) 101 65 41 A
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002 2 02 STX (start of text) 102 66 42 B
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003 3 03 ETX (end of text) 103 67 43 C
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004 4 04 EOT (end of transmission) 104 68 44 D
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005 5 05 ENQ (enquiry) 105 69 45 E
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006 6 06 ACK (acknowledge) 106 70 46 F
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007 7 07 BEL '\a' (bell) 107 71 47 G
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010 8 08 BS '\b' (backspace) 110 72 48 H
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011 9 09 HT '\t' (horizontal tab) 111 73 49 I
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012 10 0A LF '\n' (new line) 112 74 4A J
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013 11 0B VT '\v' (vertical tab) 113 75 4B K
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014 12 0C FF '\f' (form feed) 114 76 4C L
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015 13 0D CR '\r' (carriage ret) 115 77 4D M
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016 14 0E SO (shift out) 116 78 4E N
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017 15 0F SI (shift in) 117 79 4F O
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020 16 10 DLE (data link escape) 120 80 50 P
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021 17 11 DC1 (device control 1) 121 81 51 Q
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022 18 12 DC2 (device control 2) 122 82 52 R
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023 19 13 DC3 (device control 3) 123 83 53 S
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024 20 14 DC4 (device control 4) 124 84 54 T
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025 21 15 NAK (negative ack.) 125 85 55 U
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026 22 16 SYN (synchronous idle) 126 86 56 V
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027 23 17 ETB (end of trans. blk) 127 87 57 W
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030 24 18 CAN (cancel) 130 88 58 X
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031 25 19 EM (end of medium) 131 89 59 Y
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032 26 1A SUB (substitute) 132 90 5A Z
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033 27 1B ESC (escape) 133 91 5B [
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034 28 1C FS (file separator) 134 92 5C \ '\\'
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035 29 1D GS (group separator) 135 93 5D ]
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036 30 1E RS (record separator) 136 94 5E ^
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037 31 1F US (unit separator) 137 95 5F _
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040 32 20 SPACE 140 96 60 `
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041 33 21 ! 141 97 61 a
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042 34 22 " 142 98 62 b
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043 35 23 # 143 99 63 c
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044 36 24 $ 144 100 64 d
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045 37 25 % 145 101 65 e
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046 38 26 & 146 102 66 f
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047 39 27 ' 147 103 67 g
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050 40 28 ( 150 104 68 h
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051 41 29 ) 151 105 69 i
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052 42 2A * 152 106 6A j
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053 43 2B + 153 107 6B k
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054 44 2C , 154 108 6C l
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055 45 2D - 155 109 6D m
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056 46 2E . 156 110 6E n
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057 47 2F / 157 111 6F o
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060 48 30 0 160 112 70 p
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061 49 31 1 161 113 71 q
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062 50 32 2 162 114 72 r
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063 51 33 3 163 115 73 s
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064 52 34 4 164 116 74 t
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065 53 35 5 165 117 75 u
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066 54 36 6 166 118 76 v
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067 55 37 7 167 119 77 w
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070 56 38 8 170 120 78 x
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071 57 39 9 171 121 79 y
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072 58 3A : 172 122 7A z
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073 59 3B ; 173 123 7B {
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074 60 3C < 174 124 7C |
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075 61 3D = 175 125 7D }
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076 62 3E > 176 126 7E ~
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077 63 3F ? 177 127 7F DEL
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Tables
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For convenience, below are more compact tables in hex and decimal.
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2 3 4 5 6 7 30 40 50 60 70 80 90 100 110 120
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------------- ---------------------------------
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0: 0 @ P ` p 0: ( 2 < F P Z d n x
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1: ! 1 A Q a q 1: ) 3 = G Q [ e o y
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2: " 2 B R b r 2: * 4 > H R \ f p z
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3: # 3 C S c s 3: ! + 5 ? I S ] g q {
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4: $ 4 D T d t 4: " , 6 @ J T ^ h r |
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5: % 5 E U e u 5: # - 7 A K U _ i s }
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6: & 6 F V f v 6: $ . 8 B L V ` j t ~
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7: ' 7 G W g w 7: % / 9 C M W a k u DEL
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8: ( 8 H X h x 8: & 0 : D N X b l v
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9: ) 9 I Y i y 9: ' 1 ; E O Y c m w
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A: * : J Z j z
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B: + ; K [ k {
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C: , < L \ l |
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D: - = M ] m }
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E: . > N ^ n ~
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F: / ? O _ o DEL
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```
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