C

get string from ptrace registery

#include <sys/ptrace.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <linux/user.h>
#include <sys/syscall.h>
const int long_size = sizeof(long);
void reverse(char *str)
{   int i, j;
    char temp;
    for(i = 0, j = strlen(str) - 2;
        i <= j; ++i, --j) {
        temp = str[i];
        str[i] = str[j];
        str[j] = temp;
    }
}
void getdata(pid_t child, long addr,
             char *str, int len)
{   char *laddr;
    int i, j;
    union u {
            long val;
            char chars[long_size];
    }data;
    i = 0;
    j = len / long_size;
    laddr = str;
    while(i < j) {
        data.val = ptrace(PTRACE_PEEKDATA,
                          child, addr + i * 4,
                          NULL);
        memcpy(laddr, data.chars, long_size);
        ++i;
        laddr += long_size;
    }
    j = len % long_size;
    if(j != 0) {
        data.val = ptrace(PTRACE_PEEKDATA,
                          child, addr + i * 4,
                          NULL);
        memcpy(laddr, data.chars, j);
    }
    str[len] = '';
}
void putdata(pid_t child, long addr,
             char *str, int len)
{   char *laddr;
    int i, j;
    union u {
            long val;
            char chars[long_size];
    }data;
    i = 0;
    j = len / long_size;
    laddr = str;
    while(i < j) {
        memcpy(data.chars, laddr, long_size);
        ptrace(PTRACE_POKEDATA, child,
               addr + i * 4, data.val);
        ++i;
        laddr += long_size;
    }
    j = len % long_size;
    if(j != 0) {
        memcpy(data.chars, laddr, j);
        ptrace(PTRACE_POKEDATA, child,
               addr + i * 4, data.val);
    }
}
int main()
{
   pid_t child;
   child = fork();
   if(child == 0) {
      ptrace(PTRACE_TRACEME, 0, NULL, NULL);
      execl("/bin/ls", "ls", NULL);
   }
   else {
      long orig_eax;
      long params[3];
      int status;
      char *str, *laddr;
      int toggle = 0;
      while(1) {
         wait(&status);
         if(WIFEXITED(status))
             break;
         orig_eax = ptrace(PTRACE_PEEKUSER,
                           child, 4 * ORIG_EAX,
                           NULL);
         if(orig_eax == SYS_write) {
            if(toggle == 0) {
               toggle = 1;
               params[0] = ptrace(PTRACE_PEEKUSER,
                                  child, 4 * EBX,
                                  NULL);
               params[1] = ptrace(PTRACE_PEEKUSER,
                                  child, 4 * ECX,
                                  NULL);
               params[2] = ptrace(PTRACE_PEEKUSER,
                                  child, 4 * EDX,
                                  NULL);
               str = (char *)calloc((params[2]+1)
                                 * sizeof(char));
               getdata(child, params[1], str,
                       params[2]);
               reverse(str);
               putdata(child, params[1], str,
                       params[2]);
            }
            else {
               toggle = 0;
            }
         }
      ptrace(PTRACE_SYSCALL, child, NULL, NULL);
      }
   }
   return 0;
}