Uncategorized

Snooping on .NET EventPipes

While playing with EventPipes, I wanted to better understand the Diagnostic IPC Protocol. This protocol is used to transfer diagnostic data between the .NET runtime and a diagnostic client, such as, for example, dotnet-trace. When a .NET process starts, the runtime creates the diagnostic endpoint. On Windows, the endpoint is a named pipe, and on Unix, it’s a Unix domain socket created in the temp files folder. The endpoint name begins with a ‘dotnet-diagnostic-’ string and then contains the process ID to make it unique. The name also includes a timestamp and a ‘-socket’ suffix on Unix. Valid example names are dotnet-diagnostic-2675 on Windows and dotnet-diagnostic-2675-2489049-socket on Unix. When you type the ps subcommand in any of the CLI diagnostics tools (for example, dotnet-counters ps), the tool internally lists the endpoints matching the pattern I just described. So, essentially, the following commands are a good approximation to this logic:

# Linux
$ ls /tmp/dotnet-diagnostic-*
/tmp/dotnet-diagnostic-213-11057-socket /tmp/dotnet-diagnostic-2675-2489049-socket
# Windows
PS me> [System.IO.Directory]::GetFiles("\\.\pipe\", "dotnet-diagnostic-*")
\\.\pipe\dotnet-diagnostic-9272
\\.\pipe\dotnet-diagnostic-13372

The code for the .NET process listing is in the ProcessStatus.cs file. After extracting the process ID from the endpoint name, the diagnostics tool creates a Process class instance to retrieve the process name for printing. Armed with this knowledge, let’s try to intercept the communication between the tracer and the tracee.

Continue reading “Snooping on .NET EventPipes”
Uncategorized

Writing network proxies for development purposes in C#

If you are developing, testing, or supporting web applications, you probably encounter situations when you need to record or modify HTTP traffic. Quite often, the browser request viewer might be enough, but what if you need to modify the traffic on the fly? Another challenging task is testing how your application behaves when put behind a load balancer or an edge server. There are many great HTTP proxies available in the market, including mitmproxy, Burp Suite, or Fiddler and they may be perfect in diagnosing/testing your applications. In this post, however, I am encouraging you to write small tools for your specific needs. There are many reasons why you may want to do so, such as the need for complex requests modifications, better control over the request processing, or customizations of the certificate creation. Of course, implementing the HTTP protocol could be demanding so, don’t worry; we won’t do that 🙂 Instead, we will use the open-source Titanium Web Proxy. The code samples in this post are meant to be run in LINQPad, which is my favorite tool for writing and running .NET code snippets, but you should have no difficulties in porting the samples to a C# script or a console application.

Continue reading “Writing network proxies for development purposes in C#”
Uncategorized

A story of fixing a memory leak in MiniDumper

MiniDumper is a diagnostic tool for collecting memory dumps of .NET applications. Dumps created by MiniDumper are significantly smaller than full-memory dumps collected by, for example, procdump. However, they contain enough information to diagnose most of the issues in the managed applications. MiniDumper was initially developed by Sasha Goldstein, and I made few contributions to its code base. You may learn more about this tool from Sasha’s or my blog posts.

Recently, one of MiniDumper users reported a memory leak in the application. The numbers looked scary as there was a 20MB leak on each memory dump. The issue stayed opened a few weeks before I finally found a moment to look at it. As it was quite a compelling case, I decided to share with you the diagnostics steps in the hope it proves useful in your investigations.

Continue reading “A story of fixing a memory leak in MiniDumper”
Security

Randomness in .NET

There are various situations when you need random data in your application. Maybe you want to mix the order of the returned items, or maybe you create nonces for your encrypted messages. Those two sample scenarios require different approaches, and while choosing a non-cryptographic PRNG works just fine in the first situation, using it in the latter is entirely wrong. You may be wondering what a non-cryptographic PRNG is. A PRNG, or pseudorandom number generator, is an algorithm for generating a sequence of numbers whose properties almost equal to the properties of sequences of random numbers. The way how the algorithm creates these sequences could be either cryptographically secure (cryptographic PRNG) or not (non-cryptographic PRNG). A non-cryptographic PRNG cares only about the uniform distribution of random bits and not about their predictability. As we will see in a moment, using the same seed twice in the Non-crypto PRNG, results in two sequences of bytes equal to each other. Cryptographic PRNGs, on the other hand, provide random bits but are also unpredictable. In the coming paragraphs, we will examine in detail the ways we use PRNGs in .NET.

Continue reading “Randomness in .NET”