Cesar Bernardini's Blog http://www.gotext.org/people/cesar Oh Crystal Ball, tell me life is beautiful... Wed, 10 Feb 2010 15:26:13 +0000 http://wordpress.org/?v=2.8.4 en hourly 1 The SIGSEGV that has never occurred! http://www.gotext.org/people/cesar/?p=93 http://www.gotext.org/people/cesar/?p=93#comments Wed, 10 Feb 2010 15:26:13 +0000 cesarbernardini http://www.gotext.org/people/cesar/?p=93 Some days ago, I found out with an easy problem: make a program that generates a Segmentation Fault! The easiest way I thought was generate a simple buffer overflow and write on a place that it’s not mine!

The thing interesting on this post was that the program I made HAS NEVER FINISHED! and it’s really simple… Let you the code:

int main(void)
{
int i = 0;
int array[1];

while (i < 100)
{
array[i++] = 1;
printf(”%i\n”, i);
}

return 0;
}

So… Did you find out the error?

Here you got the results generated by the program

mesarpe@cesar:~/Programacion$ ./sigsegv
2
2
2
2
2
2
2
2
2

It has been compiled with gcc for 32 bits:

mesarpe@cesar:~/Programacion$ gcc -m32 -g -o sigsegv sigsegv.c

Maybe you have some skills and you find out the problem, and maybe you don’t… This program has surprised me, so… I’m gonna explain what has happened!

On ANSI-C we don’t have an specified order for the variables so the compiler has the freedom to decide where to put them on our stack. What my compiler has done was:

Here you can see where the array is saved and where the i integer

Here you can see where the array is saved and where the i integer

Well… You want to know directly from gdb the address and results:

Leyendo símbolos desde /home/mesarpe/Programacion/hack/sigsegv…done.
(gdb) b main
Interruption Point 1 at 0×80483ed: file sigsegv.c, line 16.
(gdb) r
Starting program: /home/mesarpe/Programacion/hack/sigsegv

Breakpoint 1, main () at sigsegv.c:16
16        int i = 0;
(gdb) n
20        while (i < 100)
(gdb) n
22            array[i++] = 1;
(gdb) p &array[0]
$1 = (int *) 0xbffff454
(gdb) p &array[1]
$2 = (int *) 0xbffff458
(gdb) p &array[2]
$3 = (int *) 0xbffff45c
(gdb) p &i
$4 = (int *) 0xbffff45c
(gdb) n
23            printf(”%i\n”, i);
(gdb) n
1
20        while (i < 100)
(gdb) n
22            array[i++] = 1;
(gdb) n
23            printf(”%i\n”, i);
(gdb) n
2
20        while (i < 100)
(gdb) n
22            array[i++] = 1;
(gdb) n
23            printf(”%i\n”, i);
(gdb) print i
$5 = 2
(gdb) n
2
20        while (i < 100)
(gdb) n
22            array[i++] = 1;
(gdb) p i
$6 = 2
(gdb) n
23            printf(”%i\n”, i);
(gdb) p i

What has happened is the next, when we set the array[2] value on 1, we write on the integer i value (that) is 2 and is changed to 1). So when we increment the i value, we are setting a 2 again. Curious, isn’t?

Anyway, this little code must inspire you to AVOID the Buffer Overflows, even when they are complicated!

]]> http://www.gotext.org/people/cesar/?feed=rss2&p=93 1 goText: my first XML Service! http://www.gotext.org/people/cesar/?p=88 http://www.gotext.org/people/cesar/?p=88#comments Thu, 28 Jan 2010 23:07:14 +0000 cesarbernardini http://www.gotext.org/people/cesar/?p=88 Last months on goText, Zydio was playing a lot with Qt and he has made a great application: goText++Desk, it’s awesome now you can use goText from your desktop… Anyway, that’s not all! He also has created an amazing XML system to create simple and advanced services to send SMS.

My today’s post is about how I has migrated the traditional php service to the new format :)

goText services requires two parts: a configuration and a sending part!

I will start telling about the configuration part, the old service required the next configuration:

<config><t>Envia SMS con goText</t>
<nu>0</nu><np>0</np><nn>1</nn><mr>1</mr><mc>110</mc><mm>20</mm><in>1</in>
</config>

It has 110 characters to send the SMS, It can send 20 sms per day, need a nick and got the title: Envia SMS con goText.

The configuration on the new format is done in two parts, firts we have some useful information as service name, help, max chars, version, icon, author and if it’s needed to save the session (this time it’s, remember the old script does :D ):

<service name=”Personal Argentina” xsv=”1.0.2″ version=”1″ minorversion=”1″ maxchar=”100″ require_icc=”false” savesession=”true”
icon=”http://www.personal.com.ar/favicon.ico” author=”mesarpe”>

Then, we need to set how much recipients will have:

<recipients max=”1″>
<recipient type=”phone” />
</recipients>

And then, how messages will be sent by day, which fields will be needed:

<limit type=”num” reset=”0″ />
<field required=”true” name=”sender” description=”Nick” type=”txt” />

As you can see the configuration is so much clear now :)

Now it’s time of the sending part… If we remember a little bit we got two parts:

  • Get the captcha code to fill
  • Send the captcha code and all the values

We have not an if instruction but we have fork tags that makes some checks and they detects if we are on the first or second part. Take a look at the next example:

<fork id=”captchatextsent_check”>
<condition type=”not_empty” var1=”$ic” ok_id=”4″ ko_id=”prepare_recipient” />
</fork>

It check if $ic variable is not empty then goes to page 4 (sending captcha code and sending the sms).

Another and the last thing to know! All the POST and GET connections now are made with some xml tags: the pages. The next example is the sending captcha and sms code, take a look at the var tag that makes some checks on the received page to see if the SMS has been sent:

<page id=”4″ url=”$new_url#” type=”post”>
<post name=”form_flag” value=”" />
<post name=”Snb” value=”$rcpt” />
<post name=”subname=” value=”$rcpt” />
<post name=”sig” value=”$sender” />
<post name=”msgtext” value=”$msg” />
<post name=”form” value=”ht4″ />
<post name=”size” value=”10″ />
<post name=”btn_send” value=”SEND” />
<post name=”historico” value=”" />
<post name=”Filename” value=”tmp/$captcha_filename.png” />
<post name=”FormValidar” value=”validar” />
<post name=”DE_MESG_TXT” value=”$sender” />
<post name=”sizebox” value=”43″ />
<post name=”MESG_TXT” value=”$msg” />
<post name=”codigo” value=”$ic” />
<post name=”Enviar.x” value=”41″ />
<post name=”Enviar.y” value=”16″ />
<post name=”pantalla” value=”" />
<var in=”page” name=”send_check” search=”match” match=”- a $rcpt” not_empty=”confirm” empty=”error” error_message=”Unknown send error on Personal website” />
</page>

Well… I know this is very incomplete I have not talked about variables and thousands of things that Zydio has created, but may be can help you to create your own service and it gives you a brief about the thing. On goText page we have a lot of documentation about it! You can see it.

The complete source code of the service is available on goText Sourceforge SVN Page.

]]> http://www.gotext.org/people/cesar/?feed=rss2&p=88 0 PEAR Packages: Captcha on PHP 2 http://www.gotext.org/people/cesar/?p=74 http://www.gotext.org/people/cesar/?p=74#comments Thu, 21 Jan 2010 00:01:20 +0000 cesarbernardini http://www.gotext.org/people/cesar/?p=74 Tonight, I can’t sleep so I decide to continue writing on the blog… Sorry, long time without activity… I had been concerned about CAPTCHA on gotext’s contact page since I write the last post… Well, I forget about it when I was on my holidays on San Bernardo… But the thing is…

I’m gonna explain how to use it because PEAR captcha documentation is not enough at least for me.

This is the image generated with the program

This is the image generated with the program

The first thing we need to do is find out where is the font we want to use, on ubuntu they are at:

/usr/share/fonts/X11

inside this folder, there are several folders with ttf files inside them, what you can do is copy the  font you want to use into the folder your captcha files will be. Suppose we copy any font but with the name cesar.ttf.

Then we need to create a special file that we will use to insert the image everytime we want. This file will create the session variables to save the captcha word and will print the image. The content of the file can be seen, right here:

<?
require_once ‘Text/CAPTCHA.php’;
session_start();

// Captcha options
$imageOptions = array(
'font_size'        => 20,
'font_path'        => '/var/www/contact_form/',
'font_file'        => 'cesar.ttf',
'text_color'       => '#DDFF99',
'lines_color'      => '#CCEEDD',
'background_color' => '#555555'
);

// Set CAPTCHA options
$options = array(
'width' => 250,
'height' => 100,
'output' => 'png',
'imageOptions' => $imageOptions
);

// Generate a new Text_CAPTCHA object, Image driver
$numcap = Text_CAPTCHA::factory('Image');
$ret = $numcap->init($options);
if (PEAR::isError($ret)) {
printf('Error initializing CAPTCHA: %s!',
$ret->getMessage());
exit;
}

// Get CAPTCHA image (as PNG)
$png = $numcap->getCAPTCHAAsPNG();
if (PEAR::isError($png)) {
echo 'Error generating CAPTCHA!';
echo $png->getMessage();
exit;
}

header("Content-type: image/png");
header("Cookie: PHPSESSID=".session_id());
echo $png;

$_SESSION['answer'] = $numcap->getPhrase();

?>

And here you can see the form example and how we check if the inserted image is correct:

<?php
session_start();

if (isset($_POST['captcha']) && isset($_SESSION['answer'])) {
if ($_POST['captcha'] != $_SESSION['answer']) {
$errors[] = 'Wrong solution! Please, Try Again';
}
}
if (!empty($errors)) {
foreach ($errors as $error) {
print "<h4><font color='red'>$error</font></h4><br />";
}
}
else
{
echo 'You are human!';

}

print '
<form name="capter" action="contact_form.php" method="post">
<table>
<tr>
<th>What is this result?: <img src="contact_form_ic.php" />';
print '</th>
<td><input type="text" value="" name="captcha" /></td>
</tr>
<tr>
<th/>
<td><input type="submit" value="Submit!" /></td>
</tr>
</form>
';
?>

Well... That's all, I hope you can use it and forget about SPAM, or at least... for a little time hehe

]]> http://www.gotext.org/people/cesar/?feed=rss2&p=74 0 PEAR Packages: Captcha on PHP http://www.gotext.org/people/cesar/?p=64 http://www.gotext.org/people/cesar/?p=64#comments Wed, 28 Oct 2009 19:13:43 +0000 cesarbernardini http://www.gotext.org/people/cesar/?p=64 At gotext.org, we are asking why don’t we have a Contact Form for users so I decided (after some Bluesman asks :p) to coded it… My first thought was “Oh, I need to work with CAPTCHAS“… But the problem was solved more easier than what I thought!

Detect if the system is human or not!

Detect if the system is human or not!

I had installed the pear package on my ubuntu system:

sudo apt-get install php-pear

Then I had installed the Text Captcha package on pear, puting on my ubuntu:

sudo pear install Text_CAPTCHA-0.4.0

Then… The code part:

require_once ‘Text/CAPTCHA.php’;
session_start();
$captcha = Text_CAPTCHA::factory(’Equation’);

$ret = $captcha->init();
if (PEAR::isError($ret)) {
echo $captcha->getMessage();
exit(1);
}

if (isset($_POST['captcha']) && isset($_SESSION['answer'])) {

if ($_POST['captcha'] != $_SESSION['answer']) {$errors[] = 'Wrong solution! Please, Try Again';}else{$errors[] = 'You're right! Everything went fine'; }
if (!empty($errors)) {
foreach ($errors as $error) {
print "<h4><font color='red'>$error</font></h4><br />";
}
}

print '
<form name="capter" action="contact_form.php" method="post">
<table>
<tr>
<th>What is this result?: '.$captcha->getCAPTCHA().'</th>
<td><input type="text" value="" name="captcha" /></td>
</tr>
<tr>
<th/>
<td><input type="submit" value="Send!" /></td>
</tr>
</form>
';
$_SESSION['answer'] = $captcha->getPhrase();
?>

Making it simplier... The only thing that I have done is create the captcha object, used the gethPrase function to get and save on the session cookies the solution, and getCaptcha to print the equation!

Simple don't you think?

]]> http://www.gotext.org/people/cesar/?feed=rss2&p=64 3 Remembering the Past… my first Topsites script on PHP http://www.gotext.org/people/cesar/?p=59 http://www.gotext.org/people/cesar/?p=59#comments Sat, 24 Oct 2009 23:42:44 +0000 cesarbernardini http://www.gotext.org/people/cesar/?p=59 Time ago, being more accurate I used to love PHP… It was the first language that I could do everything that I want… In a nasty way, but it was what I thought that would be the best!

So this time, checking folders I found out my best script of my beginings… Or what I thought that was a nice script hehe

Do you know how they work? You can add your website, put a button on your website (that will tell you your position at the rank) and list the best websites on a page.

Those times, I used to hate MySQL… Why? I still don’t know! So I used to save everything on flat text files. In the rar file you can find also the migrated version to MySQL because I had some problems with erasing content of flat files for concurrency things that I didn’t know that they exists hehe

This script was used on a website about Anime: Animeki, that a friend of mine had… And I don’t know anything about anime but I do know about coding, so I helped that way. Why I tell you that? Because on the code you can see some animeki codes.

Sources, here

Well… That’s all folks!

]]> http://www.gotext.org/people/cesar/?feed=rss2&p=59 4 goText: going Social! http://www.gotext.org/people/cesar/?p=57 http://www.gotext.org/people/cesar/?p=57#comments Tue, 20 Oct 2009 02:59:43 +0000 cesarbernardini http://www.gotext.org/people/cesar/?p=57 Hi people, so long since my last post… Sorry, I was my birthday and I has been busy with parties… This time, I want to talk our news at goText… Bluesman has been working a lot with Social Networks: adding support for Twitter and Facebook!

I has worked a little bit to include my put my hand on their scripts and I has created a handler, that is available from gotext.org.

Please take a look, and I really suggest to start using them to update your status on facebook and twitter! :D

More Info:

]]> http://www.gotext.org/people/cesar/?feed=rss2&p=57 0 AccelerateMe: How does acceleration works? http://www.gotext.org/people/cesar/?p=53 http://www.gotext.org/people/cesar/?p=53#comments Mon, 05 Oct 2009 21:23:00 +0000 cesarbernardini http://www.gotext.org/people/cesar/?p=53 A week ago, I was very confuse about how does the accelerometer works… So I decide to implement a nice, simple and fast PyS60 app to understand how does it works.

The result was a working and decent app, that shows three bars: x-axis, y-axis and z-axis. When you move the cellphone they react and you can see how does they change!

The source code can be downloaded from here

]]> http://www.gotext.org/people/cesar/?feed=rss2&p=53 0 Playing with Symbian C++ http://www.gotext.org/people/cesar/?p=44 http://www.gotext.org/people/cesar/?p=44#comments Fri, 25 Sep 2009 19:52:27 +0000 cesarbernardini http://www.gotext.org/people/cesar/?p=44 Today, I was playing with Symbian C++… I had been creating some Demo apps, to understand the difference to work into Python and Symbian C++…

It’s really amazing! PyS60 rulezzz… On the bottom, I give the tutorial link, I want to make at least a simple App that reminds me each 5 minutes that I have some messages pending :) I’m making my first steps… Maybe soon, I can finish it!

The link I follow for the tutorial:
http://developer.symbian.org/wiki/index.php/Going_Beyond_Hello:_A_Tutorial_for_Symbian_C%2B%2B_Applications

]]> http://www.gotext.org/people/cesar/?feed=rss2&p=44 2 Fun: Drilling my Ibook G3 http://www.gotext.org/people/cesar/?p=41 http://www.gotext.org/people/cesar/?p=41#comments Tue, 22 Sep 2009 21:37:14 +0000 cesarbernardini http://www.gotext.org/people/cesar/?p=41 Two months ago, I was begining a developing course for making a Linux Driver for a Wireless Device (VIA VT6656 USB Dongle) with an amazing hacker as Teacher, Christoph Hellwig. A requisite for doing the course was to have a Linux Computer with Kernel 2.6.30… The day before the course starts the HDD failed, and as you may know the thing gets complicated when the time is running and some sinks over the iBook seems to be UNHEADED!!!

So as everyone should do… That was the result… hehe

The machine is still working, I will upload an image showing soon :D
Bye people!!

PS: Don’t do it!… It really hearts, even when the machine is 10 years old hehe

]]> http://www.gotext.org/people/cesar/?feed=rss2&p=41 2 pyLine: Testing the Rotation Sensor http://www.gotext.org/people/cesar/?p=38 http://www.gotext.org/people/cesar/?p=38#comments Mon, 21 Sep 2009 17:48:29 +0000 cesarbernardini http://www.gotext.org/people/cesar/?p=38 As you may know, I’m becoming more and more addicted to new technology and when this kind of things start to happened, you try to understand every new piece that appears.

Well… Rotation Sensors are not something new, but it’s my first time having a cell phone that contains one… So, I has decided to code a simple script to test it.

The script is coded on PyS60 (Python for S60), and it’s a simple line that always stays on vertical position :)

Rotation Sensor handles the X, Y and Z axis, but at this simple demo I has been working only with the Z one. I let you a picture showing what does the program do:

pyLine demo usage

pyLine demo usage

Well… That’s all I hope you like it. I let you the link to download the Python file, here.

]]> http://www.gotext.org/people/cesar/?feed=rss2&p=38 0