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Picking Apart the Crashing iOS String

manishearth.github.io

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Re: Picking Apart the Crashing iOS String

#61

Post by glibgil »

stcredzero wrote: post #37
jrochkind1 wrote: post #31

What I'm really curious about is how bugs/errors in the iOS typesetting algorithm result in a crash, rather than just wrong or nonsense typesetting -- and how the last time this happened, they appearently just fixed the specific case, but not the ability of bugs/errors in the typesetting algorithm to crash the system. I am not surprised there will be errors/bugs in the typesetting algorithm, as the OP demonstrates, t…

you'd think you'd want to make sure they didn't cause hard crashes. Any Apple people want to chime in? Why wasn't the general bug -- where there could be even the possibility of a "text crash" -- fixed?

If Apple people chime in I think they get beheaded. It never happens

Re: Picking Apart the Crashing iOS String

#62

Post by ghusbands »

stcredzero wrote: post #37
jrochkind1 wrote: post #31

What I'm really curious about is how bugs/errors in the iOS typesetting algorithm result in a crash, rather than just wrong or nonsense typesetting -- and how the last time this happened, they appearently just fixed the specific case, but not the ability of bugs/errors in the typesetting algorithm to crash the system. I am not surprised there will be errors/bugs in the typesetting algorithm, as the OP demonstrates, t…

you'd think you'd want to make sure they didn't cause hard crashes. Any Apple people want to chime in? Why wasn't the general bug -- where there could be even the possibility of a "text crash" -- fixed?

You realize that there's no such thing as "don't ever crash" fix, right? Maybe they added some defensive code and maybe they didn't, but if they're using an unsafe language, there's always the possibility of more such issues.

Re: Picking Apart the Crashing iOS String

#63

Post by blackflame7000 »

Manishearth wrote: post #55
blackflame7000 wrote: post #40

Does anyone else think that this could be related to Auto-Correct having problems with the malformed expressions?

This happens whenever the system is asked to render text; it doesn't have to be editable. (it's just easier to trigger in text boxes because you paste and that's it)

Oh, gotcha. Yea not sure auto-correct could cause that. I initially read it was only related to text-entry and thought auto-correct was likely since it was affecting multiple apps indicating an OS issue.

Re: Picking Apart the Crashing iOS String

#64

Post by ghusbands »

blackflame7000 wrote: post #56
arbie wrote: post #53

Earlier quoted context omitted.

Why would Auto-Correct kick in on incoming texts or on browser pages?

I read that it was related to text-boxes so I figured that could be a potentially hidden culprit. I haven't heard of web pages crashing due to embedded text but if so then I retract my hypothesis. 2nd Sentence of the article says text box but not sure what "other places" are: "Basically, if you put this string in any system text box (and other places), it crashes that process."

From the article's source article: "iMessages, [...] Facebook Messenger, WhatsApp, Gmail, and Outlook for iOS [...] can become disabled once a message is received". "It might be difficult to fix and delete the problem message".

From the article: "I’ve been testing it by copy-pasting characters into Spotlight so I don’t end up crashing my browser". "I can cause this crash to happen more reliably in browsers by clicking on the string".

So, not text-box specific and happening on display for a wide variety of applications, including web pages.

Re: Picking Apart the Crashing iOS String

#65

Post by enzanki_ars »

gsich wrote: post #60
enzanki_ars wrote: post #47

Earlier quoted context omitted.

Ah. Forgot that existed for some reason. (Windows/Linux user that gets screwed out of programming for my own phone. Hate that....)

Use Hackintosh or a VM.

Given that Apple does not design their OS to work on anything but their hardware, the pain I would incur trying to set up either option is just not worth it. Unless someone has published a stable and updated pre-built VM for macOS, it just seems like nothing but trouble.

Re: Picking Apart the Crashing iOS String

#66

Post by tinix »

nottorp wrote: post #22
spaceywilly wrote: post #5

Earlier quoted context omitted.

My question was, why was there not a unit test for this? It seems like it would be trivial to step through every character combination for each language they support and make sure it doesn't cause a crash.

I bet they have unit tests for all emojis...

this comment is under-rated. haha, you know it's true.... and sad.

Re: Picking Apart the Crashing iOS String

#67

Post by pkaler »

jrochkind1 wrote: post #31

What I'm really curious about is how bugs/errors in the iOS typesetting algorithm result in a crash, rather than just wrong or nonsense typesetting -- and how the last time this happened, they appearently just fixed the specific case, but not the ability of bugs/errors in the typesetting algorithm to crash the system. I am not surprised there will be errors/bugs in the typesetting algorithm, as the OP demonstrates, t…

The crash seems to be in CoreText. CoreText is embedded/linked in Messages, Spotlight, Springboard, etc. CoreText is written in C.

The fix would be to rewrite CoreText in a memory safe language like Swift. This would be “hard”. Or put CoreText in an XPC container. This would both be “hard” and result in terrible performance.

For more details on how hard C, memory management, systems programming, and operating system development is please refer to your local copy of Modern Operating Systems by Andy Tannenbaum.

Re: Picking Apart the Crashing iOS String

#68

Post by Manishearth »

bonzini wrote: post #21
perkee wrote: post #19

Earlier quoted context omitted.

This sequence begins the Telugu word for "knowledge" so maybe someone texted that to someone and it went viral from there. This is, of course, only speculation.

Does the word include the zwnj character? How do you input it?

It does not include the zwnj, that somehow snuck in. Most keyboards don't support directly inputting a zwnj, but may support it for specific combinations. For example my Marathi keyboard supports typing eyelash rephs (e.g. in र्‍क) which includes zwj.

However I'm not aware of any such things in Telugu aside from explicit virama-showing which rarely exists in input methods (and doesn't end up with zwnj in the position shown here, but that could have happened after editing).

Re: Picking Apart the Crashing iOS String

#69

Post by saagarjha »

glibgil wrote: post #61
stcredzero wrote: post #37

Earlier quoted context omitted.

you'd think you'd want to make sure they didn't cause hard crashes. Any Apple people want to chime in? Why wasn't the general bug -- where there could be even the possibility of a "text crash" -- fixed?

If Apple people chime in I think they get beheaded. It never happens

They do sometimes, but generally not for topics such as these.

Re: Picking Apart the Crashing iOS String

#70

Post by mapmap »

pkaler wrote: post #67
jrochkind1 wrote: post #31

What I'm really curious about is how bugs/errors in the iOS typesetting algorithm result in a crash, rather than just wrong or nonsense typesetting -- and how the last time this happened, they appearently just fixed the specific case, but not the ability of bugs/errors in the typesetting algorithm to crash the system. I am not surprised there will be errors/bugs in the typesetting algorithm, as the OP demonstrates, t…

The crash seems to be in CoreText. CoreText is embedded/linked in Messages, Spotlight, Springboard, etc. CoreText is written in C. The fix would be to rewrite CoreText in a memory safe language like Swift. This would be “hard”. Or put CoreText in an XPC container. This would both be “hard” and result in terrible performance. For more details on how hard C, memory management, systems programming, and operating system…

I'm guessing C is how they get the performance they need. Re-writing in Obj-C or Swift would likely have speed tradeoffs.
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