Linux programming to your program back door

        Switch (args[0][0])//parse instruction to see what each instruction corresponds to {case ' d '://display switch (args[1][0]                    {case ' Q '://display queue show_mq (FD);                    Break                    Case ' d '://display debug Show_debug_level (FD);                     Break                        Default:help_manual (FD);                Break             } break;                    Case ' s '://set switch (args[1][0]) {case ' d '://set debug level  n = atoi (args[2]);                    Converts a string to an integer fprintf (FD, "debug level changed from%d to%d", global.debug_level,n);  Global.debug_level = n;                     Change log level break;                        Default:help_manual (FD);                Break             } break; DefAult:help_manual (FD);        Break  }

Iv. Building the Debug interfaceFirst on the interface diagram:

Every command we knock is passed through the interface to the end of the program, such as "D D" indicates that the current system is running at the log level, and "s D" is to set the log level we want to see, so that we can implement the program through the backdoor dynamic modification of the program. So how do you implement this seemingly simple interface? To implement this interface, there are several key points:

• We need to redirect the printout of the program to a file.
• Read the contents of a file using a shell script
• The command we entered needs to be written to the FIFO.

The above three points are the most important technical issues for the interface.

1. REDIRECT Output

At first I was going to redirect the standard output and standard error to the amount in the file, but think about it, or want to directly print the content directly to the file. such as this:

     FD = fopen ("/vob/ljsdpoenew3/exercise/debug_log2", "w+");    if (fd = = NULL)    {        my_log (DEBUG, "open debug_log2 fail!\n");        Pthread_exit (0);    } fprintf (FD, "debug level change from%d to%d", global.debug_level,n);

In this way, the print generated by Debug Center is output to the file debug_log2.

2. Read the content with a script and write the content to the FIFO

To do this requires a simple knowledge of shell programming, how do we put our input into the FIFO? How do we read the contents of the log file and display it on the display? I think the first is to write another client, for interprocess communication, write the command to the FIFO, but also read the contents of the log file. However, I found that using the shell can do the above, and it only takes a few lines of code.

#!/bin/bash my_inp_fifo=/vob/ljsdpoenew3/exercise/debug_log    # Specify FIFO file Stty erase ^h while     [true];d o         Read INP    #循环读入用户输入        If ["$inp" = = "Quit"];then   #quit代表结束该界面                exit 0        fi        echo $inp > $my _inp_ FIFO   #写入fifo        cat debug_log2.txt         #显示log的内容done

Let's see how this command-line interface runs! First we run the server process
The sever process constantly generates messages and processes messages.  We open another window and execute the script./test.sh, enter the interface we used the D command to see the debug level of the program at this time, using the D q to see the program message queue situation. We used the S-d instruction to set the debug level to 0, when the screen did not have any printout, and when we used the S-d instruction to set levels to-1 (all positions one), all the print classes were turned on and the screen began to print wildly. Also said that we control the program through the backdoor, here we just modified the log level of the program, of course, we can do more things, as long as the framework to the inside with instructions, and corresponding processing operations, can be achieved. v. SummaryThe so-called back door, is a can control the program interface, this interface is only for developers debugging development, not open to customers. So the back door has a huge effect, so it's a great tool for developers to debug programs. Some people will think, I want to use a socket instead of FIFO for process communication can not, so you can do remote host control program. I think it is possible, but it is more secure to use Telnet to the destination host and then run the script operation. Finally, the source code framework is given.

  1 #include <stdio.h> 2 #include <string.h> 3 #include <stdlib.h> 4 #include <math.h> 5 #incl  Ude <sys/types.h> 6 #include <sys/stat.h> 7 #include <sys/prctl.h> 8 #include "msg_def.h" 9 #include "Global.h" Ten queue_t msgqueue; extern dashboard_t Global; #define Max_num_args #define MAX_ARGS_SIZE (Args[max_num_args][max_args_size]) ;     The static int Get_args (FILE *inputfile,file *fd) {24 char tmpbuffer[100]; char *line = Tmpbuffer; Char separator[] = ", \n\t"; *token Char; int i; + char EOF; int num = 0; EOF =!fgets (line, sizeof (Tmpbuffer), inputfile); if (EOF) return num; memcpy (tmpbuffer2,tmpbuffer,100); The Panax Notoginseng token = strtok (line, separator); (Num < Max_num_args && tokens), strcpy (Args[num], token);num++; token = strtok (NULL, separator); (i = num; i < Max_num_args; i++) args[i][0] = 0; if (num > 0) {fprintf (FD, "%s", TmpBuffer2); Help_manual (file* fd), (FD, "\nd d:display current Debu G level\n "); fprintf (FD, "D q:display msg Queue Length, head and tail\n"); fprintf (FD, "s d [level]: Set debug [level] \ n"); (file* fd) show_mq {fprintf (fd, "msg queue length:%d head:%d tail:%d \ n", ABS (Msgqueue . head-msgqueue.rear), msgqueue.head,msgqueue.rear); Show_debug_level (file* FD), fprintf (FD, "Current debug Level:%d\n", Global.debug_leve L); The "Debug_center" () () () () () () () () () () (rc,num,n), file* FP, file* FD; DEBUG, "hi,debug!\n"); 85 86 System ("Rm/vob/ljsdpoenew3/exercise/debug_log"); System ("RM/VOB/LJSDPOENEW3/EXERCISE/DEBUG_LOG2"); Mkfifo rc = ("/vob/ljsdpoenew3/exercise/debug_log", 0666);     if (RC < 0) My_log (DEBUG, "make FIFO fail!\n"), Pthread_exit (0); 94} 95 96 fp = fopen ("/vob/ljsdpoenew3/exercise/debug_log", "R");   if (fp = = NULL) 98 {my_log (DEBUG, "open Debug_log fail!\n"); pthread_exit (0); 101}102 103 FD = fopen ("/vob/ljsdpoenew3/exercise/debug_log2", "w+"); 104 if (fd = = NULL). {106 My_log (debug , "Open debug_log2 fail!\n"); 107 pthread_exit (0); 108}109//freopen ("/vob/ljsdpoenew3/exercise/debug_log2.             TXT "," w+ ", FD), 111 fprintf (FD," \n==================================================\n "), fprintf (FD," Welcme to Debug center! ");   113 fprintf (FD, "\n==================================================\n\n"); help_manual (FD); 115  Fflush (FD); 117 while (1) 118 {119 fflush (FD); fprintf (FD, "\n\nmy_diag>"); 121 num = Get_args (FP,FD), 122 if (num < 1) 123 {124 Freopen ("/vob/ljsdpoenew3/exercise/debug_log"         , "R", FP), Fflush (FD), 126 continue;127}128 fprintf (FD, "\n\nmy_diag>"); 129                 Switch (args[0][0]) [131 case ' d '://display132 switch (args[1][0]) 133                     {134 case ' Q '://display queue135 show_mq (FD); 136                     break;137 case ' d '://display debug138 show_debug_level (FD); 139                         break;140 141 default:142 help_manual (FD); 143 break;144}145 break;146 147 case ' s '://set148 switch (ARG             S[1][0]) 149    {case ' d '://set debug level151 n = atoi (args[2]); 152                     fprintf (FD, "debug level change from%d to%d", global.debug_level,n); 153 Global.debug_level = n;154                         break;155 156 default:157 help_manual (FD); 158 break;159}160 break;161 162 default:163 Help_manu Al (FD); 164 break;165}166 167}168}

Linux programming to your program back door