print shell code

From the book “Buffer Overflow Attacks” by Foster and others, I came across this very handy tool for testing developing shellcode.  It takes your assembly and puts it into a well commented C array to be tested by execution or simply printing to the screen.

To compile thes program, type gcc -o printshell printshellcode.c

Now, if you want to try out your shellcode assembly,

  • Type the instructions in a .S file
  • Execute nasm -o <filename> <filename>.S
    • To print the shellcode use printshellcode -p <filename>.
    • To execute the shellcode use printshellcode -e <filename>
/*printshellcode.c*/

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
/*Print message function*/
static void croak(const char *msg){
    fprintf(stderr, "%s\n", msg);
    fflush(stderr);
}

/*Usage funcion*/
static void usage(const char *prgnam){
    fprintf(stderr, "\nExecute code : %s -e \n", prgnam);
    fflush(stderr);
    exit(1);
}

/*Signal error and bail out*/
 static void barf(const char *msg){
    perror(msg);
    exit(1);
}

/*main*/
int main(int argc, char **argv){

    FILE	*fp;
    void	*code;
    int		i,l,arg;
    int		m=15; /* max number of bytes on a line*/

    struct stat sbuf;
    long	flen; /*assume files are &lt; 2**32*/
    void	(*fptr)(void);

    if(argc &lt; 3) usage(argv[0]);
    if(stat(argv[2], &amp;sbuf)) barf(&quot;failed to stat file&quot;);
    flen = (long) sbuf.st_size;
    if(!(code = malloc(flen))) barf(&quot;failed to grab enough memory&quot;);
    if(!(fp = fopen(argv[2], &quot;rb&quot;))) barf(&quot;failed to open file&quot;);
    if(fclose(fp)) barf(&quot;failed to close file&quot;);

    while ((arg = getopt (argc, argv, &quot;e:p:&quot;)) != 1){
      switch(arg){
        case 'e':
          croak(&quot;Calling code ...&quot;);
          fptr = (void (*)(void)) code;
          (*fptr)();
          break;
        case 'p':
          printf(&quot;\n/* The following shellcode is %d bytes long: */\n&quot;,flen);
          printf(&quot;\nchar shellcode[] = \n&quot;);
          l = m;
          for(i = 0; i= m){
              if(i) printf("\"\n");
              printf( "\t\"");
              l = 0;
            }
            ++l;
            printf("\\x%02x", ((unsigned char *)code)[i]);
          }
          printf("\";\n\n\n");
          break;

        default:
          usage(argv[0]);
      }
    }
    return 0;
}

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