How to execute an object file: Part 3
September 10, 2021 12:58 PM
Continue learning how to import and execute code from an object file. In this part we will handle external library dependencies....
How to execute an object file: Part 2
April 02, 2021 11:00 AM
Continue learning how to import and execute code from an object file. This time we will investigate ELF relocations....
A deep-dive into Cloudflare’s autonomous edge DDoS protection
March 18, 2021 2:18 PM
Introducing our autonomous DDoS (Distributed Denial of Service) protection system, globally deployed to all of Cloudflare’s 200+ data centers, and is actively protecting all our customers against DDoS attacks across layers 3 to 7 (in the OSI model) without requiring any human intervention....
Conntrack turns a blind eye to dropped SYNs
March 04, 2021 12:00 PM
We have been dealing with conntrack, the connection tracking layer in the Linux kernel, for years. And yet, despite the collected know-how, questions about its inner workings occasionally come up. When they do, it is hard to resist the temptation to go digging for answers....
How to execute an object file: Part 1
March 02, 2021 12:00 PM
Ever wondered if it is possible to execute an object file without linking? Or use any object file as a library? Follow along to learn how to decompose an object file and import code from it along the way....
MORE POSTS
September 18, 2020 11:00 AM
Raking the floods: my intern project using eBPF
SYN-cookies help mitigating SYN-floods for TCP, but how can we protect services from similar attacks that use UDP? We designed an algorithm and a library to fill this gap, and it’s open source!...
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July 08, 2020 11:00 AM
Sandboxing in Linux with zero lines of code
In this post we will review Linux seccomp and learn how to sandbox any (even a proprietary) application without writing a single line of code....
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April 06, 2020 11:00 AM
Conntrack tales - one thousand and one flows
We were wondering - can we just enable Linux "conntrack"? How does it actually work? I volunteered to help the team understand the dark corners of the Linux's "conntrack" stateful firewall subsystem....
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March 25, 2020 12:00 PM
Speeding up Linux disk encryption
Encrypting data at rest is vital for Cloudflare with more than 200 data centres across the world. In this post, we will investigate the performance of disk encryption on Linux and explain how we made it at least two times faster for ourselves and our customers!...
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March 19, 2020 12:57 PM
Keepalives considered harmful
You’d think keepalives would always be helpful, but turns out reality isn’t always what you expect it to be. It really helps if you read Why does one NGINX worker take all the load? first....
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March 18, 2020 12:00 PM
The problem with thread^W event loops
Back when Cloudflare was created, the dominant HTTP server used to power websites was Apache httpd. However, we decided to build our infrastructure using the then relatively new NGINX server....
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October 12, 2019 1:00 PM
It's crowded in here!
We recently gave a presentation on Programming socket lookup with BPF at the Linux Plumbers Conference 2019 in Lisbon, Portugal....
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July 18, 2019 2:12 PM
A Tale of Two (APT) Transports
Securing access to your APT repositories is critical. At Cloudflare, like in most organizations, we used a legacy VPN to lock down who could reach our internal software repositories. However, a network perimeter model lacks a number of features that we consider critical to a team...
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July 10, 2019 1:07 PM
A gentle introduction to Linux Kernel fuzzing
For some time I’ve wanted to play with coverage-guided fuzzing. I decided to have a go at the Linux Kernel netlink machinery. It's a good target: it's an obscure part of kernel, and it's relatively easy to automatically craft valid messages....
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May 30, 2019 1:00 PM
Cloudflare Repositories FTW
Kali Linux turned six years old this year! In this time, Kali has established itself as the de-facto standard open source penetration testing platform....
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May 18, 2019 3:00 PM
Cloudflare architecture and how BPF eats the world
Recently at I gave a short talk titled "Linux at Cloudflare". The talk ended up being mostly about BPF. It seems, no matter the question - BPF is the answer. Here is a transcript of a slightly adjusted version of that talk....
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May 03, 2019 1:00 PM
eBPF can't count?!
It is unlikely we can tell you anything new about the extended Berkeley Packet Filter, eBPF for short, if you've read all the great man pages, docs, guides, and some of our blogs out there. But we can tell you a war story, who doesn't like those? ...
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April 24, 2019 6:21 PM
xdpcap: XDP Packet Capture
Our servers manage heaps of network packets, from legit traffic to big DDoS attacks. For top efficiency, we adopted eXpress Data Path (XDP), a Linux kernel tool for swift, low-level packet handling....
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January 04, 2019 11:02 AM
io_submit: The epoll alternative you've never heard about
The Linux AIO is designed for, well, Asynchronous disk IO! They are not network sockets, but is it possible to use Linux AIO API with network sockets? The answer is a strong YES! ...
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