Slashdot Mirror
Typing These 8 Characters Will Crash Almost Any App On Your Mountain Lion Mac
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."
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.
> An obscure library bug triggered by a magic string.
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.)
Cut that out, or I will ship you to Norilsk in a box.
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.
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.
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.