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Linux Kernel Back-Door Hack Attempt Discovered
An anonymous reader writes "The BitKeeper to CVS gateway was apparently hacked in an attempt to add a root exploit back door to the Linux kernel, according to the linux-kernel archive. The change was in the file kernel/exit.c and changed the user ID of a process to root under the guise of checking the validity of some flags. The core Linux BitKeeper kernel repository was not at risk, and in fact it was the BitKeeper CVS export scripts that detected the unauthorized modifications to CVS. The changes were falsely attributed in CVS to long-time Linux developer davem (David Miller). Users of the BKCVS repository should resync their trees to remove the offending code if they had replicated it since yesterday."
Good to see the system works. You would wonder what would happen if said hacker was working for a company on a similar closed source program. Would it have been detected?
Someone has some damned big balls to do something like that...
Let's hope they're cut off.
This statement is false.
Sounds like a plan to get the dirty GNU/hippies to upgrade to the real BitKeeper instead of using the communist CVS gateway.
That McVoy is a smart one!
Did you know his programmers need to feed their families and pay their mortgages? Very sad situation, I hope everybody buys 10-15 licenses ASAP.
No, but I'd like to see them claim copyright infringement on back-door code.
Waiting for ad.doubleclick.net...
Why not just establish a web-o-trust and sign patches?
That way people who hack in won't be able to send in signed patches to the system [e.g. even if they physicially update the tree others can trivially spot the unsigned patches].
That would of course, require people to actually think about security in terms of "oh sure people won't hack it because it hasn't been done...much...before."
Tom
Someday, I'll have a real sig.
I'll call ESR, he's got the guns.
You guys get Linus and make sure he brings Tove, since she could probly kick all our asses.
Once thats done we'll Larry McVoy, by this time hopefully he will have the IP of the slimeball.
The Pose rides at Dawn, we can kill some Trolls along the way.
Did Glenn Beck rape and kill a girl in 1990? gb1990.com
In my code I always put the constant on the lhs so that the difference between the equality (==) and assignment (=) operator are caught by the compiler by accident.
if ((options == (__WCLONE|__WALL)) && (current->uid = 0))
In this case, it would make an attempted root hole more visible, as (0 = current->uid) would not compile.
The actual lines of code and the method by which they got there were far too clever for either Microsoft or SCO. In particular, it looked like a check for an invalid combination of flags by root, but would actually set the process to root in the case of the invalid combination of flags (and the error return value would be overwritten).
The intent was probably that a CVS user get the bad version, work on other stuff, and send the diff (including the bad lines) to a maintainer in an otherwise good patch. However, the BKCVS gateway got confused by someone other than it changing the CVS, and complained, and Larry McVoy pointed out the issue, someone asked what the lines were, and other people figured out what they'd do. Now, of course, if someone had gotten that bit accidentally and submitted it to a maintainer, they'd notice, so the attempt seems to have failed.
Linus pointed out a benefit to using BK: even if the official BK repository were changed, he doesn't pull from it (because his local copy has all of his changes), and he would get an error the next time he pushed to it. The repository that would have to be attacked is actually his local disk, behind a firewall and not set up for anyone else to access at all.
If RMS wants to rant about revision control systems, he'll need to say that CVS needs to be replaced with a more functional alternative (Subversion, perhaps), not BK.
Yes, everyone who's upset about exploits they haven't heard about, raise their hands...
"that's not encryption - it's a new perl script that I'm working on..." - from some Matrix parody
Isn't the pertinent question... was this the first?
My God! It's full of stars!
1 x 4 x 9
That monolith... oh... kernel.... right...
Stop the Slashdot effect! Don't read the articles!
Keep reading the thread - you'll read a bid of Linus, and a comforting explaination of whats happenin' back there.
No, you don't understand. This exploit was disguised as error checking code. It'd stick out in Longhorn like a sore thumb.
Just because you're paranoid doesn't mean there isn't an invisible demon about to eat your face
The Ultimate Backdoor, if anyone hasn't read about it:
Reflections on Trusting Trust.
You might want to doublecheck that gcc code you're compiling the kernel with...
As noted on LKML, (current->uid = 0) was probably deliberately surrounded by brackets to avoid a gcc warning of an assignment within a test.
I'm not so sure about that. Personally I would have put the brackets there even in case of a normal test. They might not be necesarry, but I trust brackets more than I would trust my own ability to remember the precedence of every operator in C.
Do you care about the security of your wireless mouse?
The "backdoor" that someone attempted to submit was a local privilege elevation bug, not a remote compromise.
Insightful my ass. Nowhere does it say CVS was exploited.
The code was injected into a CVS tree, the box could have been compromised in another fashion, such as a wu-ftp hole or some such thing.
So please, don't throw the word exploit around as if you have 1/2 a clue about security. It just makes you look silly to those of us who do.
I see some people posting some negative replies, or lamenting on OSS process, etc and saying how it didnt work, or how a psuedo-trusted patch would get in, if it went through proper channels, or some such crap.
this couldn't be further from the truth, you are all forgetting many things, #1 - the checking scripts run daily now, and Larry has mentioned he's going to step that up, still fixed within 24hrs is a damn good response time! closed-source could never be this fast.
#2 - all this talk of peer review, saying it didn't catch this or whatever nonsense, yes in a way it did, and whats more it's exactly what will keep semi-valid attempts or those through "proper channels" out of the code. You forget, millions of people around the world review this stuff, and someone, somewhere will find it relatively quickly, and not just because all the good developers (which is most of the millions) really LIKE linux and do their utmost to protect it, and ensure that no twits do things like this.
on the oft-side billions to one chance someone does something stupid like people said hire someone to do good patches for a long time, get trusted, and submit a patch with this kind of code in it, well, first of all, this is just stupid, it would take years to get that trusted from "zero", second, even assuming all that, the code would still get caught very quickly.
Like I said, someone, somewhere is gonna notice real quick, because the millions of us out in the world really happen to LIKE linux, and protect the kernel most of all, and I'm sure as the code worked its way into the tree, one of the people would catch it, and I'd be willing to bet several would see it at the same moment, including Linus, et all.
You simply can't pull a fast one over the great coders we have, these aren't your average coders, and remember, not just them, but all of us, really, in a way, put our heart and soul into supporting Linux, its a confidence we dont share lightly, the kernel is the most protected of it all, yes, for obvious reasons, its the most critical code.
But even outside the kernel, remember millions of people around the world are reviewing code 24hrs a day, every day, and posting notes about issues, patches, etc.
It's simply much harder to get by all that. Like I said, and I'll say it again, someone's gonna notice, and probably LONG before it even gets into the main BK tree, because even those reviewers ain't slouches!
Closed source has a smaller review team, and I know for a fact internal developers add back-doors to code all the time. I know many closed-source coders (not necessarily personally) that as a matter of habit throw in back-doors into every piece of code they write, because they hate their job, and the people they work for, and hate the product. Since very few people ever review the code, things can sit there indefinately and never get found.
remember this is a work of pride, something the community really cares about, we really want to see it succeed, and not have the issues like this, or that others have, we want to protect it at all costs, in any way, to ensure a good future, and protect the users out there.
remember, we're users too! If it means that much to you, wouldn't you be checking it too? damn straight! This is exactly why the OSS model is so damn important,
and its exactly why Microcrap, SCO, etc will never "get" it. I'd even add Intel to this list, because I think AMD is really "getting" it.
summary - we like it, we care about it, and aint no way we gonna let some dork attempt to ruin something we've worked so damn hard to build, not just for ourselves, but for everyone, its a matter of pride.
and yes, anyone found out (and they will be!) doing this shit is gonna get their ass kicked into next week...
Microsoft insists the timing of their bounty (pay deal) on (for) virus writers (hackers) "entirely coincidental" (damned convenient)
Curiosity was framed. Ignorance killed the cat.
You're missing something. They use bitkeeper, the CVS repository for people without CVS.
Its separate so they can screen CVS commits carefully.
The actual lines of code and the method by which they got there were far too clever for either Microsoft or SCO
It was a subtle change but I think it would have been caught if it had been submitted to Linus. He does review code and often catches mistakes. In this case assignment was used in a condition. To good C programmers this is bad taste. I noticed that right off and I haven't written a line of C in about 6 years. Linus isn't just a good C programmer. After half a decade of watching him catch stuff like this in just his public LKML messages, I'm convinced he would have seen this if he were reading braille hardcopy of it from across the room while drunk.
Maw! Fire up the karma burner!
The vandal who put this in the CVS code tree obviously had a lot of skill.
It's a clever backdoor, and might have gone unnoticed, if not for those those good automated checks in the BitKeeper-to-CVS gateway. Notice that the particular coding style is a common C gotcha (using "=", assignment, instead of "==", comparison). At first glance it looks like the value of uid is being compared with 0, when in actuality it is being assigned the value of 0: root! The gcc compiler is good about warning for this, except that this too has been defeated: as mentioned on the mailing list, notice the unusual high number of parenthesis around this expression. That high number of parenthesis has the effect of suppressing the gcc compiler warning.
So, whoever did this obviously knew what they were doing and tried to obfuscate it. As somebody else mentioned on the kernel mailing list, if somebody is going to put in a backdoor like this, why not make it a remote root hack?
As it is now, the above hack is only locally exploitable. A process on the local system still has to call the wait system call with that particular combination of flags, in order to trigger the exploit and get root. To my knowledge, no known applications do this, because the combination of flags is supposed to be invalid.
If a spammer or somebody else was trying to backdoor the Linux kernel in order to gain a large number of machines to infest, then one wonders why they didn't put in a remote root exploit. It seems strange to go to all the trouble. Since this backdoor attempt has been caught and blocked, security will now only become tighter, and they might not ever get another chance like this.
Maybe it was intended to be used with another application, also backdoored in the same manner? It might be insightful to scan other open source applications and search for this particular usage of flags to the wait system call.
In any case, I'm glad this hack was caught!
Dr. Demento On The 'Net!
Should end the old argument about which is better, the habitual, easy to read, but easy to screw up or abuse:
if(variable == CONSTANT) { }
Or the safe version that's so much harder to screw up and which turns out to be just as easy to read with practice:
if(CONSTANT == variable) { }
Do we all understand the real world significance of this now?
If you still want to advocate (variable == CONSTANT), then please feel free to prove that no accidental or abusive (variable = CONSTANT) exist in the kernel.
If you were blocking sigs, you wouldn't have to read this.
Of course, at some point, we do have to trust someone.
Ken Thompson wrote an original speculative essay on this for CACM back in 1984 of all years.
It is really well worth the read. The short form is that there exists a way to subvert the compiler such that it is no longer trustable and it will build a back door into the OS forevermore. This paper is a must read.