some bugs

[luojiaqs]

I'm learning ftp protocol find some bugs and just make a mark don't mind ^ ^

ftp_pwd

result size 大小没控制好造成stackoverflow

void ftp_pwd(Command *cmd, State *state)
{
  if(state->logged_in){
    char cwd[BSIZE];//size 1024
    char result[BSIZE];//size 1024
    memset(result, 0, BSIZE);
    if(getcwd(cwd,BSIZE)!=NULL){
      strcat(result,"257 \"");//size 5
      strcat(result,cwd); //  maybe size 1024
      strcat(result,"\"\n");//size 2
        //result size max == 5 + 1024 +2
      state->message = result;
    }else{
      state->message = "550 Failed to get pwd.\n";
    }
    write_state(state);
  }

ftp_mkd

same problem as ftp_pwd strcat stack overflow

if(mkdir(cmd->arg,S_IRWXU)==0){
        strcat(res,"257 \"");
        strcat(res,cmd->arg);
        strcat(res,"\" new directory created.\n");
        state->message = res;

sprintf use %s can also cause stack overflow when len(cwd)+len(cmd->arg)>1024

sprintf(res,"257 \"%s/%s\" new directory created.\n",cwd,cmd->arg);