Typing These 8 Characters Will Crash Almost Any App On Your Mountain Lion Mac 425
An anonymous reader writes "All software has bugs, but this one is a particularly odd one. If you type "File:///" (no quotes) into almost any app on your Mac, it will crash. The discovery was made recently and a bug report was posted to Open Radar. First off, it’s worth noting that the bug only appears to be present in OS X Mountain Lion and is not reproducible in Lion or Snow Leopard. That’s not exactly good news given that this is the latest release of Apple’s operating system, which an increasing number of Mac users are switching to. ... A closer look shows the bug is inside Data Detectors, a feature that lets apps recognize dates, locations, and contact data, making it easy for you to save this information in your address book and calendar."
printf (Score:2, Funny)
Let's look at the stack trace (Score:5, Informative)
This is the stack trace mentioned in the article:
http://pastebin.com/UkhERvaA [pastebin.com]
Doesn't look like a c-string or printf issue to me at all.
Re:printf (Score:5, Insightful)
Nope. Lousy programmers strike again. There's nothing at all wrong with c-strings. There is, however, a sufficiency of lousy programmers who lack the skill to handle perfectly simple data structures. Seriously, if you can't handle a zero terminated string or keep from overrunning an array, it's not the string format that's the problem. It's you.
Assuming the problem here is a string problem may be jumping the gun, too. Could just as easily be something else.
Re:printf (Score:5, Funny)
I like C, but the problem is that most programmers cause chaos when they write it. C was always meant as a language that people who like assembler will like and use and be more productive. It was not meant as a language that today's script monkeys should use.
Also Objective C was designed according to the prinicples of Objectivism - i.e. the code of the looters and moochers would crash and burn and bankrupt their companies whereas the code of Great Men would navigate the formidable obstacles of pointers and demonstrate their status as Nietzschean Ubermenschen and be rewarded with tonnes of cash and Patricia Neal, so this is not really surprising.
Re:printf (Score:5, Informative)
Not likely. It crashes due to an assertion failure and subsequent exception being thrown.
Re: (Score:3, Informative)
Not likely. It crashes due to an assertion failure and subsequent exception being thrown.
Yeah. Data Detectors on Macs is just like Semantic Desktop on KDE. When I make a fresh install of the OS, disabling these pesky little "features" is one of the first things I do. I'm glad somebody somewhere out there finds them useful but I definitely don't.
Re:printf (Score:5, Funny)
Here speaketh the Apple fan. No matter what... it's a good thing.
Re:printf (Score:5, Insightful)
as a programmer myself, when coding something and a harmless and not completely unexpected input occurs, your program shouldn't crash, due to any reason, asserts included. Such a failure is sign of nothing but lazy programming and even lazier unit testing.
Re:printf (Score:5, Informative)
as a programmer myself, when coding something and a harmless and not completely unexpected input occurs, your program shouldn't crash, due to any reason, asserts included. Such a failure is sign of nothing but lazy programming and even lazier unit testing.
Sorry, but you are wrong.
By the time you fail an assertion, you better crash because you're not supposed to be there. The code in FRONT of the assertion is supposed to prevent that.
Assertions go between the input checking front, and the sane input needing rear. Their only purpose in life is to prevent an unknown state in the rear guts, not to do what should have been done up front.
Comment removed (Score:5, Insightful)
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Re:printf (Score:5, Insightful)
A perfect program should not crash for any reason - but very few programs of any considerable size are perfect. And even well-written software has bugs.
Asserts are meant to indicate that the condition should always be true on this particular code path - that's why it's called an "assert". It's not a tool to check for exceptional conditions and gracefully handle them - you have conditional statements (and exception handling, if the language supports that) for those purposes. You use assert after you have used a conditional to fork off onto a code path to assert that all the implied conditions are, indeed, true. If the conditions are not true, it indicates a bug in the logic of the program - the assumption was not correct. There is no way to gracefully handle that, because you don't know where exactly the problem is, and therefore you can no longer rely on the state of your process being correct. If you hit an assert, it means that some objects you thought to be alive are now dead, and you might have dangling pointers around. Or maybe some variables that you think have correct values in them have something outdated and completely irrelevant. Either way, if you keep running, you risk integer and buffer overflows - and from there, execution of arbitrary injected code. From security perspective, this is the worst scenario you can end up with, especially for an application facing the network or processing external inputs from the network. Fast-fail (i.e. consistently crashing right away) is much preferable to that, even if it inconveniences the user.
Re:printf (Score:5, Informative)
You don't understand what assert() is for.
It doesn't cause a crash. Quite the opposite. It is a way of deliberately causing program termination upon encountering an internal inconsistency; precisely so as to avoid a crash, a silent failure or some other undesirable behavior.
Obviously, in a bug-free program, assert() would never trigger and is therefore unnecessary. In the real world it is a useful safety net.
Note that assert() is sometimes used to catch runtime errors. That is indeed inappropriate. But you shouldn't condemn the tool because it is sometimes used incorrectly.
Re:printf (Score:5, Informative)
I used to think the same way about kernel panics in an operating system - I thought there was no reason why the system should ever halt. And then I had an OS class, where it was pointed out that halting is a quite valid choice when encountering an error condition that indicates that something has gone fundamentally wrong. For example, if you have an allocation bitmap that tells you what parts of your disk is in use, and what parts are free, it has a checksum, and the checksum is incorrect. It may very well be that the safest thing to do in this case is halt, rather than risk a write making it to the disk and overwriting a block that is in use. The user can reboot, and that will probably be the best way to recover from the error. It might be possible to display an error message, however since the code to display such a message is not often used, it's likely still on the disk (it was either never loaded, or was loaded and then swapped out of RAM). So you might think it's safe to try to read the disk still - but you have to set some state somewhere saying that under no circumstances should you write anything while you try to load this code. But what's to say that whatever state you set is working? Obviously something is broken, your checksum was wrong! And for that matter, if you need to swap something else out to load this new code in, you can't, because you've decided that writes are now unsafe. For that matter, maybe the disk is acting up - maybe it'll interpret a read command as a write, or take some other completely bogus action. Or maybe what you think is your memory-mapped disk is now really the network card, because some CPU configuration registers picked up a bad value. Bottom line; there are definitely good reasons to just stop a program, OS, or whatever when you detect an error that should never happen.
That said, this case is not one of those good reasons.
Re:printf (Score:5, Informative)
Then instead of an assert you should have a return error (or throw exception) statement.
No. Those can only ever be for foreseen error states. If they are not foreseen, then they are no documentable, and therefore the calling code can take no sensible action to react to the error or exception.
An assert is a documentation of something that's always true and will never fail. If it fails, that's a bug, and there's no graceful handling of bugs - if you could foresee them, you would have already fixed them.
The question is whether to only have them in debug builds or whether to have them in release builds too. Contrary to your ASSERTION, asserts aren't necessarily compiled out of release builds. The answer is they go in release builds too if the worst case scenario is data corruption from continuing in an unpredictable state.
None of this is in Programming 101. This is stuff you learn when you've been programming a long time.
Re:printf (Score:5, Informative)
And yet, unchecked input is the root of almost all software vulnerabilities
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assert should be compiled away in production code. :-)
Comment removed (Score:4)
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as a programmer myself, when coding something and a harmless and not completely unexpected input occurs, your program shouldn't crash, due to any reason, asserts included. Such a failure is sign of nothing but lazy programming and even lazier unit testing.
Whoa there!
1. Don't worry about the harmless. WORRY about the HARMFUL ... thank you Capt'n Obvious. Now quick: think of three things a program can do that are worse than crashing.
2. Don't worry about the "not completely unexpected". That is, of course, the expected. WORRY about the UNEXPECTED
3. "your program shouldn't crash"
Bzzzt. Time's up. Did you get: (1) Have exploitable security flaws; (2) Corrupt or delete data; (3) Hang or livelock. There are others.
Cheers.
Re:printf (Score:5, Informative)
I have also had the impression that assert() is a hack that shouldn't be used much (?).
$ man assert
NAME
assert -- expression verification macro
SYNOPSIS
#include
assert(expression);
DESCRIPTION
The assert() macro tests the given expression and if it is false, the
calling process is terminated. A diagnostic message is written to stderr
and the abort(3) function is called, effectively terminating the program.
If expression is true, the assert() macro does nothing.
The assert() macro may be removed at compile time with the cc(1) option
-DNDEBUG.
Somebody forgot to remove some debugging code, embarrassing but hardly something that hasn't happened before and definitely not the end of the world as we know it.
Re:printf (Score:5, Insightful)
assert() isn't really "debugging code". It's more of a sanity check - as the name implies, it's a macro that checks that expression is indeed true, where the standing assumption on this particular code path is that it must be true. If it's not true, then there's a logic bug somewhere in the program, and that may lead to data corruption or worse. So liberally sprinkling asserts around and leaving them in release builds actually helps - it's far better to fast-fail than to continue running the process in a potentially corrupted state, from security perspective.
Of course, the assert shouldn't be triggered in the first place - the fact that they somehow got into this state is itself a bug, which they should fix. Still, kudos to Apple folk for handling this one in a manner that makes it useless for an exploit.
Re:printf (Score:5, Insightful)
In your release build, it should never be hit. But unless you can absolutely guarantee it, leave it there. You will make mistakes, and it's better to handle them in a safer manner.
If it's hit, your program is in a state that you have not foreseen when writing it. If you're using assert for its intended purpose, then you're claiming: "I expect this condition to always be true here; the following code is written with this assumption in mind". If the condition is somehow not true, then the following code is a bug/exploit farm, and should not be allowed to run. You might also want to phone home, yes (though e.g. on Windows, WER will do it for you if you register for it). You definitely don't want to do nothing.
Re:printf (Score:5, Insightful)
Based on what you said, the summary title is incorrect. The programs aren't crashing, but rather are ending normally, just not when the user thinks they're telling it to.
It is easy to argue that while this is technically a "normal" shutdown given the code of the program; it is certainly not a normal shutdown given the task and role of the program.
You know: Letter of the law versus spirit of the law.
Your program can only execute the letter of the law (its code), but its true purpose should always be the spirit (its intended role). Otherwise, any bug inside the program would need to be considered as a "normal program exit", as the bug is an inevitable result of its code. Since that is obviously not the case:
This assert being thrown IS a bug, and the subsequent application exit not a normal shutdown. There is nothing to defend here as being "good".
Re:printf (Score:4, Insightful)
I have also had the impression that assert() is a hack that shouldn't be used much (?).
It should be used rather a lot. Every time you believe you know something will always be true, but might break if it wasn't, you should put an assert there.
There's no point putting an IF there, because you can't forsee the case where it will be taken. Likewise an exception - exceptions are for foreseen error states. And ignoring it will result in a harder to find bug if that belief is ever wrong.
It's pretty rare when the bug exists in the assert, rather than the main code. Rarer still when it's an assert that is active in release builds. This is one of those cases. But it doesn't mean that asserts are a bad thing.
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I have also had the impression that assert() is a hack that shouldn't be used much (?).
It's a hack that should be used extensively - in development code. In the production build, you generally turn on a compiler flag that prevents asserts from being compiled. This is why it's absolutely criminal to put code in an assert that has any side effects whatsoever.
Re:printf (Score:5, Insightful)
Yes, input validation is usually a good thing and no amount of you hating Apple Inc is going to change that.
That's true. But a crash is not the way to handle invalid input.
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I agree with you, you couldn't abort on bad input.
However, based on my interpetation of what is happening, this isn't what is happening. My expecation is as follows:
The user types something in an address bar.
That string is passed to hypothetical function 'process_uri'.
'process_uri' sees that it is a file uri, and passes it to the hypothetical function 'process_file_uri'.
'process_file_url' sees that it wasn't given a file uri, and aborts.
The problem ISN'T that the use gave bad input. If process_uri was given
Re:printf (Score:5, Insightful)
Hence, the programmer fucked up, and this isn't input checking. It is nevertheless, IMO; a good practice to assert things (in debug code), but it also isn't checking for valid inputs, it's checking for programmer stupidity.
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I think I'd worry about security (think dangling pointers and integer/buffer overflows in case your data isn't in a state you expect it to be) before worrying about ease of reverse engineering in pretty much every scenario I can think of. In the end, if someone really cares that much about my code, they will reverse engineer it one way or another - by tracing all the way through the assembly, if necessary. Weaker security, on the other hand, means potential problems for users of my code - i.e. my employer's
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This is terminated because the program did not expect to see an URI with such capitalization, and (presumably) doesn't have code to handle it correctly - leading to an unexpected state where you can no longer be certain of the data. It indicates a bug (they forgot to handle different capitalization correctly, and they forgot to do proper user input validation), yes. But the way it handles that program bug, until such time as it's fixed, is absolutely correct.
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What is funnier that file:/// doesn't work.
The Captil F is required. at least in my limited testing.
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What is funnier that file:/// doesn't work.
The Captil F is required. at least in my limited testing.
Typing 'file:///' opened Finder.app from Safari's address bar just fine on my machine.
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Re:printf (Score:5, Informative)
A bad string isn't exceptional
Especially when the interpretation of that "bad string" is supposed to be CASE INSENSITIVE and the "exception" occurs because one character is upper case.
URI are defined here [ietf.org], and the part that deals with the "file:" or "http:" part (called the "scheme") says this:
Emphasis mine.
This is a case of a programmer implementing a feature defined in a standard and ignoring the standard when doing so. Not lazy, just ignorant and stupid. Just like the ignorant stupid programmers who write javascript email address verifiers that refuse to accept valid email addresses because they contain characters like '+'. Those programmers should be shot.
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When you detect that your program is in an inconsistent state, is it better to continue executing, possibly corrupting data and granting an attacker access to your system, rather than aborting the program and providing a stack trace to help diagnose why things went wrong?
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Re:printf (Score:5, Insightful)
No, it's better to return an error or thrown an exception rather than assert when the input to a function is perfectly reasonable but not what you expect.
And, in the end, who knows. Maybe it was the caller aborting by not handling the error/exception. In which case it's STILL bad coding by someone, as this is not an exceptional case...
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You can remove asserts because your program is NEVER supposed to rely on them. The following code:
assert(foo!=null); //do something
is WRONG. Because it depends on the assert. The correct way to code it is
if(foo == null){ //do something
assert(false);
return some_error_value;
}
Crashing is NEVER acceptable. And you cannot assume its ever an option in a production system- when you crash cleanup code is not necessarily run, and you can leave the system
Apple's response (Score:5, Funny)
You're doing it wrong.
no big deal.
Steve
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damnit, I just ran out of mod points, too... +infinity for you.
Re:Apple's response (Score:5, Funny)
Steve is in the iCloud now. Someone tried turning him off and then back on again. In an appeal to hipsters, he's gone underground to sell more macs. He is permanently 404. There is no way he could have had anything to say about this. There is no app for that. Get it? :P
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My response:
Steve is dead and has been for over a year. Time for some new jokes.
Re:Apple's response (Score:4, Funny)
BRB (Score:5, Funny)
BRB, heading down to the Apple Store...
Re:BRB (Score:4, Insightful)
Typing the string has the same effect on the app as quitting the app. So.... have fun going to the apple store and quitting the apps.
Re:BRB (Score:4, Informative)
It produces a nice exception error message. Perfect for making Apple fanbois who claim that Macs never crash look like twats.
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I know, I can be dangerously addictive sometimes.
Re: BRB (Score:2)
Powerpoint summary of TFS (Score:5, Funny)
- In the latest version.
Re:Powerpoint summary of TFS (Score:5, Insightful)
The thing is, the magic string in question is not particularly obscure. Any app that normally handles URLs is fairly likely to get that typed into it at some point. Okay, granted, protocols are usually not capitalized, and File:/// is no more common than Http:// or Mailto:, but nonetheless, this is something people are definitely going to run into occasionally.
(Yes, file protocol terminates the protocol with just two slashes; but, importantly, the next segment of the URL is an absolute path. So while the third slash would be a typo on a multi-rooted system like Windows or VMS, it's pretty much mandatory on a single-rooted system that uses slash as a directory separator -- like, say, anything with Unix underpinnings.)
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Just a thought, using something like vnc from a mobile device would make it more likely to happen since keyboards on most smartphones/tablets capitalize the first letter in anything it thinks is a sentence.
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[citation needed]
On my computer (Windows 7), in Windows Explorer, these all work the same:
file://C:/
file:///C:/
file:////////////////C:/
These also work the same:
file://
file:///
file:////////////////
Little light on specifics.... (Score:2)
Re:Little light on specifics.... (Score:5, Interesting)
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I just crashed it in 10.8.2 by simply typing it (exactly as specified) into the document area in TextEdit.
Comment removed (Score:4, Funny)
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That was sarcasm, right?
Anyway, I have twelve examples of file:/// in my browser history, all of them automatically generated by scripts. If I ever meet a script that capitalizes "File" then we may be in trouble.
So, how can I type it for them? (Score:2)
No one should ever need to type file:///
There are no bugs. You're doing it wrong
Yes, they are doing it wrong, by typing file:/// in lowercase, or not typing it at all. So the obvious question is: "how can I type it right for them?" If I include "File:///" in an email I send to a Mountain Lion user, will it crash his Mail.app? Or if someone quotes it in a reply here?
That could become a cool little meme.
Re:You're doing it wrong (Score:5, Funny)
Maybe he's using a Mac. The first two times he tried that message, Safari crashed.
Sure enough (Score:2, Informative)
So? (Score:5, Insightful)
Talk about over-egging the pudding. You're talking as if it's a fundamental flaw that ruins the whole operating system. It's a bug. Of course it's not good news, but it's not certain doom for Mountain Lion either.
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Speak for yourself - I just rolled back to Tiger!
The cause, and a fix (Score:5, Informative)
Landon Fuller has posted a gist on GitHub with an explanation of the bug and a binary patch to the affected library [github.com].
Re:The cause, and a fix (Score:4, Insightful)
Landon Fuller has posted a gist on GitHub with an explanation of the bug and a binary patch to the affected library [github.com].
Yeah, THERE'S a good idea - apply a binary patch from some random post on Slashdot!
you obviously didn't read it (Score:4, Informative)
It's a commented assembly listing with a proposed hacky fix in assembly.
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Not happening for me (Score:2)
Running OS X 10.8.2 here, and I tried it in TextEdit, Mail, and Safari.. no crash.
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Running 10.8.2 here also and it crashes in TextEdit when simply typing the text into the document - LOL!
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Just to be sure, I type file:/// into TextEdit or a new Mail message or whatever and it's supposed to crash?
Gödel Lives! (Score:3, Insightful)
Similar feature in Windows (Score:2)
It works (Score:2)
Doesn't crash Terminal (Score:2)
Even crashes the crash reporter! (Score:5, Funny)
I tried this in Safari on Lion. Capital F required, but indeed just "File:/// " crashes it.
Then you get a pop-up asking if you want to report the problem to Apple? Sure.
But then that crashes with a pop-up reporting that crash reporter has crashed. Bonus!
It's the old Windows 98 bug all over again. (Score:3)
You used to be able to BSOD a Windows 95 or 98 machine by trying to read C:\con\con, and this included any web pages that requested file://C:/con/con.
I actually typed it, and nothing happened (Score:2)
I searched in the Finder (iMac running 10.8.2) and got nothing strange. I tried Chrome, Firefox, Safari, Mail, a few text editors ... nothing. Sorry.
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Oh, wait, capitol F. That does cause a crash. Since when has a Mac been case sensitive? I guess that's what they get for listening to all those hackers complain about case insensitivity. ;)
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From a comment above, the problem is that it's not case sensitive, except for an internal sanity check which is.
E.g. the dispatching code said "the user typed File:/// and I have a handler for file:///, so I'll call it", but then the handler had what was basically an case-insensitive comparison assert(url.startswith("file:///")).
So the problem isn't case sensitivity or insensitivity -- it's that it was being inconsistent about it.
didn't some thing like @sony crash mac os 6? (Score:2)
didn't some thing like @sony crash mac os 6?
Why is Apple shipping non-optimized code? (Score:4, Insightful)
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asserts are there to catch bugs. Not invalid user input or other conditions that you can predict and gracefully handle, but actual programmer bugs - mistakes in the logic of the program.
If you ship your code with asserts disabled, you are, effectively, asserting that your code is bug-free. If you don't feel confident enough to make such a claim, then leaving them in there is a good idea - you lose a wee bit of perf, yes, but if things do go wrong, the user (and therefore you, when the user files a bug repor
Re:Why is Apple shipping non-optimized code? (Score:4, Insightful)
And that, people, is why operating systems have become so grotesquely bloated and gigantic. An endless accumulation of "oh it's only a few more bytes".
Progress (Score:2)
It is case sensitive (Score:4, Informative)
After trying this in every app I could think of, and failing to crash them, it turns out that this is case sensitive.
Some dude has done a more detailed analysis over on github [github.com] but the long and short of it is that there is a specific check in the code for 'file://' and any other case will cause it to crash. All caps - crash. Capital F and the rest in lower-case - crash. All lower-case and a capital L - crash.
it's an old joke (Score:4, Funny)
"Doctor, it hurts when I do this... Can you help me?"
"Sure, don't to that."
I'm going to give some free advice to users of Apple's OSX Mountain Lion: Don't do that.
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You are holding it right. The others aren't.
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Crashes textedit
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Crashes Safari (address bar)
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The bug is case sensitive; as the bug report says "The capital 'F' is important."
Please do not bother posting something so quickly, without looking into it.
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Technically, any capitalization other than 'file:///' will do it. File, fILE, or FILE all have the same effect. The problem is the code compares the string to 'file://' without converting to lower case first...oops.
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Technically, any capitalization other than 'file:///' will do it. File, fILE, or FILE all have the same effect. The problem is the code compares the string to 'file://' without converting to lower case first...oops.
Some code has figured out that the user entered a file url. A sanity check (badly programmed) figures out (wrongly) that it is _not_ a file URL. That wouldn't be a problem; I would have coded it so that something that looks like a file url but doesn't pass sanity checks is just not a file url. The problem is that this code throws an exception that isn't caught.
A note to C++ programmers: Convention in Objective-C is that exceptions are thrown to indicate programming errors. Exceptions are not handled by c
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It's not a buffer overflow or anything like that. Some address-reading library happens to have a sanity test that makes a naive assumption; when it catches a file URL, it tests the prefix against the string 'file://'. When the strings don't match (because of a simple case difference) the sanity test fails and the program is shut down. Oops.
It *is* a dumb bug (aren't they all?), but I doubt it could anyone could make a remote code exploit out of that.
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> I doubt it could anyone could make a remote code exploit
> out of that.
Perhaps not that precisely but what else is that library call (or whatever it is) doing that might be exploitable?
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Spotlight, too.
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I realise this is a troll, but for anyone thinking it might be real:
He's just need to restart Textedit, and all the documents he had open will still be there, still opened, in exactly the state they were in seconds before the crash. Snow Leopard documents don't need saving, they are constantly persisted whilst editing. Even if you have't yet given them a filename.