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Uncovering a 24-year-old bug in the Linux Kernel

497 点作者 greenonion超过 4 年前

14 条评论

qchris超过 4 年前
Besides being a great technical write-up, this does an absolutely fantastic job of doing low-key recruitment for Skroutz. It shows some of the main tools and technologies that the company uses on a day-to-day basis, provides a window into the way that they approach problems, makes a compelling case that you&#x27;d be working with some talented engineers, and showcases a culture willing to engage with the open source community.<p>The hiring pitch isn&#x27;t in your face, but there&#x27;s a &quot;We&#x27;re hiring!&quot; button in the banner, which fairly unobtrusively follows you down the page, and then ends with a &quot;hey, if you&#x27;re interested in working with us, reach out.&quot; Overall, it just feels really well done.
gerdesj超过 4 年前
Great write up. Think I&#x27;ll get the kids, sorry technicians to walk through this. Actually, I think I&#x27;ll learn just as much but I have to keep a little bit aloof as MD!<p>Networks are tricky to run and networking is proper hard to do. TCP&#x2F;UDP int al are pretty bloody good at shuffling data from A to B. I find it quite amusing when 20 years is considered old for a bug.<p>The Millenium bridge in London is a classic example of forgetting the basics - in this case resonance and being too clever for your own good. It&#x27;s a rather cool design for a bridge - a sort of a suspension bridge but flatter and some funky longitudinal stuff. I&#x27;m a Civ Eng grad. It looked too flat to me from day one.<p>When people walk across a bridge and it starts to sway, they start to lock step and then resonance, where each step reinforces the last kicks in and more and more energy causes sway, shear and what have you forces. It gets worse and worse and then failure. Tacoma Narrows is another classic example of resonance but due to wind - that informed designs that don&#x27;t fly!<p>Civ Eng is way, way older than IT and we are still learning. 24 years is nothing for a bug. However, IT is capable of looking inward and monitoring itself (unit tests, ping etc) in a way that Civ Eng can&#x27;t (OK we have strain gauges and a few other tools).<p>The real difference between physical stuff and IT is that the Milli bridge rather obviously came close to failure <i>visually</i> and in a way that our other senses can perceive - it shook. The fix was to put hydraulic dampers along its length.<p>In IT, we often try to fix things by using magic or papering over flaws with &quot;just so&quot; stories. Sometimes we get the tools out and do the job properly and these boys and girls did just that: the job properly.
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rancor超过 4 年前
I have, admittedly old and very vague, memories of people talking about rsync being &quot;hard on networks&quot; or &quot;dealing poorly with congestion.&quot; I&#x27;d put good odds that this bug is why those statements existed.
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zackmorris超过 4 年前
I just want to send kudos to them. I lost 2 years trying to write a reliable stream over UDP back in the days of Zoidcom and similar, maybe 2005. I don&#x27;t know how to stress this enough but...it&#x27;s basically an impossible challenge.<p>This writeup represents the depths that an engineer has to go to get real work done. I&#x27;m familiar with the integer wraparound comparison issue, and all of the other errata around TCP windowing. Thankfully countless people have done this work and we&#x27;re able to enjoy the fruits of their labor today.<p>Not sure where I&#x27;m going with this, but I&#x27;ve been programming for 30 years, and to this day, I view kernel developers and the people who isolate these bugs as the very best among us.
rob74超过 4 年前
Great writeup, and also thoroughly answers the first question that popped into my mind: &quot;how on earth could a bug in the Linux network stack that causes the whole data transfer to get stuck stay undiscovered for so long?&quot;
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tryauuum超过 4 年前
I have seen an ancient &quot;drop packets with zero-length tcp window&quot; rule in iptables in my company. Funny enough to learn that zero-length tcp window can be found in normal, non-malicious packets!
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guenthert超过 4 年前
Impressive detective work and documentation.
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leesalminen超过 4 年前
I wonder is this is the cause of a nasty NFSv3 issue I was having years ago where clients would periodically hang indefinitely, necessitating a system reboot. At the time, we were ingesting large videos on the client and transferring to a shared volume via nfs.
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janselman超过 4 年前
Great write up. It&#x27;s common to add retry or reconnect mechanism to connections even there is no requirement. It&#x27;s basically &quot;restart your computer&quot; to see if the issue disappears. So, it actually hides bugs for decades :)
bjeds超过 4 年前
Wow, superb writeup, thank you author for writing it and the submitter for posting it!
lykr0n超过 4 年前
wow. We&#x27;ve run into rsync bugs like this and just chalked it up to &quot;things happen&quot;
SeriousM超过 4 年前
This was a great article! I wonder why such problems don&#x27;t show up on windows.. is it because they have so many developers or that windows has to reboot at least every two weeks?
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db48x超过 4 年前
Great find, and it sounds like a great place to work.
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__bjoernd超过 4 年前
Great writeup!