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this post was submitted on 19 Jul 2024
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How can all of those zeroes cause a major OS crash?
If I send you on stage at the Olympic Games opening ceremony with a sealed envelope
And I say "This contains your script, just open it and read it"
And then when you open it, the script is blank
You're gonna freak out
Ah, makes sense. I guess a driver would completely freak out if that file gave no instructions and was just like "..."
Except "freak out" could have various manifestations.
In this case it was "burn down the venue".
It should have been "I'm sorry, there's been an issue, let's move on to the next speaker"
Except since it was an antivirus software the system is basically told "I must be running for you to finish booting", which does make sense as it means the antivirus can watch the system before any malicious code can get it's hooks into things.
I don't think the kernel could continue like that. The driver runs in kernel mode and took a null pointer exception. The kernel can't know how badly it's been screwed by that, the only feasible option is to BSOD.
The driver itself is where the error handling should take place. First off it ought to have static checks to prove it can't have trivial memory errors like this. Secondly, if a configuration file fails to load, it should make a determination about whether it's safe to continue or halt the system to prevent a potential exploit. You know, instead of shitting its pants and letting Windows handle it.
It was more like "barricade the doors until a swat team sniper gets a clear shot at you".
Hmmmm.
More like standing there and loudly shitting your pants and spreading it around the stage.
The envelope contains a barrel of diesel and a lit flare
Computers have social anxiety.
You're right of course and that should be on Microsoft to better implement their driver loading. But yes.
The driver is in kernel mode. If it crashes, the kernel has no idea if any internal structures have been left in an inconsistent state. If it doesn't halt then it has the potential to cause all sorts of damage.
Great layman's explanation.
Maybe. But I'd like to think I'd just say something clever like, "says here that this year the pummel horse will be replaced by yours truly!"
Problem is that software cannot deal with unexpected situations like a human brain can. Computers do exactly what a programmer tells it to do, nothing more nothing less. So if a situation arises that the programmer hasn't written code for, then there will be a crash.
Poorly written code can't.
In this case:
Is just poor code.
When talking about the driver level, you can't always just proceed to the next thing when an error happens.
Imagine if you went in for open heart surgery but the doctor forgot to put in the new valve while he was in there. He can't just stitch you up and tell you to get on with it, you'll be bleeding away inside.
In this specific case we're talking about security for business devices and critical infrastructure. If a security driver is compromised, in a lot of cases it may legitimately be better for the computer to not run at all, because a security compromise could mean it's open season for hackers on your sensitive device. We've seen hospitals held random, we've seen customer data swiped from major businesses. A day of downtime is arguably better than those outcomes.
The real answer here is crowdstrike needs a more reliable CI/CD pipeline. A failure of this magnitude is inexcusable and represents a major systemic failure in their development process. But the OS crashing as a result of that systemic failure may actually be the most reasonable desirable outcome compared to any other possible outcome.
This error isn't intentionally crashing because of a security risk, though that could happen. It's a null pointer exception, so there are no static or runtime checks that could have prevented or handled this more gracefully. This was presumably a bug in the driver for a long time, then a faulty config file came and triggered the crashes. Better static analysis and testing of the kernel driver is one aspect, how these live config updates are deployed and monitored is another.
In which case this should've been documented behaviour and probably configurable.
If AV suddenly stops working, it could mean the AV is compromised. A BSOD is a desirable outcome in that case. Booting a compromised system anyway is bad code.
I agree that the code is probably poor but I doubt it was a conscious decision to crash the OS.
The code is probably just:
And 2 fails unexpectedly because the data is garbage and wasn't checked if it's valid.
You can still catch the error at runtime and do something appropriate. That might be to say this update might have been tampered with and refuse to boot, but more likely it'd be to just send an error report back to the developers that an unexpected condition is being hit and just continuing without loading that one faulty definition file.
I'm gonna take from this that we should have AI doing disaster recovery on all deployments. Tech CEO's have been hyping AI up so much, what could possibly go wrong?
What are the chances that Crowdstrike started using ai to do their update deployments, and they just won't admit it?
Nice analogy, except you'd check the script before you tried to use it. Computers are really good at crc/hash checking files to verify their integrity, and that's exactly what a privileged process like antivirus should do with every source of information.
I'm nominating this for the "best metaphor of the day" award.
Well done!
The funny bit is, I'm sure more than a few people at Crowdstrike are preparing 3 envelopes right now.
This guy ELI5s
Because it's supposed to be something else
At least a few 1's I imagine.
What if we put in a 2
Society isn’t ready for that
Well, you see, the front fell off.
The file is used to store values to use as denominators on some divisions down the process. Being all zeros is caused a division by zero erro. Pretty rookie mistake, you should do IFERROR(;0) when using divisions to avoid that.
I disagree. I'd rather things crash than silently succeed or change the computation. They should have done better input and output validation, and gracefully fail into a recoverable state that sends a message to an admin to correct. A divide by zero doesn't crash a system, it's a recoverable error they should 100% detect and handle, hot sweep under the rug.
Life pro tip: if you're a python programmer you should use try: func() except: continue every time you run a function, that way ypu would never have errors on your code.
Lol.
Maybe they should use a more appropriate development tool for their critical security platform than Excel.
Well, the file shouldn't be zeroes
The front of the file fell off