New Linux Kernel Crash-Exploit discovered

Ant writes " According to linuxreviews article's on 6/11/2004, there is a nasty bug that lets a simple C program crash the kernel (2.4.18-2.6.x reported so far), effectively locking the whole system. Affects both 2.4.2x and 2.6.x kernels on the x86 architecture. This exploit can be compiled and run without a root access and with a shell access. There are detailed information and source code mentioned. " You need to have shell access to run this program; it's also worth noting that not *all* flavors are vulnerable. Please read article for the full details.

Comments

There's a big difference...

[Allen Zadr]

Here is a perfect example of the difference between the Open Source way and a proprietary way.

There are goods and bads, however, the information is readily available. There are patches that "work", even before a full explanation is available. Now, thousands of people are actively working on a solution, if they so choose. If they don't choose, they can use the proprietary code method - wait for the official vendors to release a patch.

In proprietary land, a vendor would first sue the person who released the information. Then, the re-iteration that you won't be vulnerable if you use a "properly configured firewall," then they'd start working on a fix.

Re:There's a big difference...

[cgenman]

I love how "properly configured firewall" is the solution to everything. Hackers root your box? You didn't have a properly configured firewall. System eaten by a worm? You should have had a properly configured firewall. Your windows box zombified and sending out spam? Seriously consider investing in a properly configured firewall.

Forget the firewall, get a properly implemented system.

Re:There's a big difference...

[Donny Smith]

>Windows users don't tend to care.

Or "Windows users tend not to care?"

Incidentally currently I'm a (primarily) Windows user and I do patch (actually it's "install updates") when Windows tells me they're ready (if I estimate I need the particular update).

Claiming that Windows users "don't care" just because they're Windows users is incorrect, to say the least.
How can people mod that as insightful? Generalization like that should be discouraged as it is not constructive, but some actually reward it... Quite puzzling to me..

Re:There's a big difference...

[Ford Prefect]

You know why? Windows users don't tend to care. They don't read Windows news sites daily, they don't subscribe to mailing lists that send out warnings as soon as a vunerability is found. They don't patch when Windows tells them to.

Sudden thought - is there much of a Windows 'community', or has it all fragmented into myriad different areas?

That's possibly one aspect in security that's often overlooked; for instance, when the recent Mac OS X vulnerabilities became known, word went around the Mac community very quickly, and people discovered new aspects of the problems, created workarounds like Paranoid Android...

There's something very similar with Linux as well - but is there a Windows equivalent of, say, Slashdot? Do Microsoft-oriented community discussion sites exist, complete with flamewars over widget styles in Microsoft Word, etc etc etc?

Or do you have to be an underdog for such a thing to exist?

Re:There's a big difference...

[Rectum2003]

What he is saying is that most Windows users are the masses that don't actually care. Other OSes don't have this problem due to the fact that they are mostly used by geeks that understand why it is so important to update your OS (any OS for that matter). Not to say that there are not millions of consciencious users (like you) who actually have a clue and know how to secure and patch a Windows machine, of course.

Re:There's a big difference...

[grahamlee]

I think it's probably just fair to say that the number of Linux-scriptkiddie wannabies is as nonzero as the number of Windows-scriptkiddie wannabies, and that a trivial piece of code guaranteed to crash any Linux/x86 system is attractive to any number of scriptkiddies. They just chose to crash someone else's machine instead of their own - I went for trying it out on the latter and have since modified the kernel on that machine. Note though that the phrase "lame free-shell provider" is not attributable to the author of TFASA, who does go on to say "this is illegal in most parts of the world and strongly discouraged". That phrase was probably passed on to them by some skiddie who wanted to go "hey look at me i am so l33t it's unbelievable i can like read gcc-bug and everything!!!11".

Re:There's a big difference...

[Verteiron]

Real simple answer to that; you are not a typical Windows user.

The vast majority of Windows users behave exactly as the grandparent post states. I know this because I deal with the results every day in my shop. I'd guess that 80% of the machines I see are in due to spyware and virus problems that could have been fixed with a patch available weeks earlier. More often than not, when I get these systems up and running, the first thing that happens is "*pop* Windows has downloaded updates and is now ready to install them." So the updates were already downloaded, waiting for the user to click "Install"... but the user never did, for reasons already mentioned.

Automatic patching on XP Home would be doing end-users (and the internet!) a huge favor.

Re:There's a big difference...

[Len Budney]

I love how "properly configured firewall" is the solution to everything. Hackers root your box? You didn't have a properly configured firewall. System eaten by a worm? You should have had a properly configured firewall. Your windows box zombified and sending out spam? Seriously consider investing in a properly configured firewall.

I've come up with the final word in firewall technology. What I do is connect my PC to the DSL router with a 10' ethernet cable. Then, using an approved tool, I carefully cut the cable, making sure to sever it completely. Haven't had a problem since.

What we really need is an article suggesting how I can speed up my downloads...

Re:There's a big difference...

[gfxguy]

You get that impression but there are a lot of slashdot users, even ones that use Linux (like me) who will defend MS when appropriate.

That said, it does seem to be true that a Linux patch will appear a lot more quickly than an MS patch, and that seems to be a result of the fact that it's open source.

Re:There's a big difference...

[the_mad_poster]

Yea, the only difference is that in OSS the steps are usually covered in about a third the time.

This hit the kernel-list dated 2004-06-09 21:02:57 . It is now 2004-06-14 09:41:12 in my neck of the woods, and it is patched. The last update mentioned on the article's page is yesterday. It would appear the patch was available in no more than 4 days. It takes more than four days for a lot of vendors just to look at the goddamn report. Then they spend the next week hoping it goes away on it's own. Then they ignore the follow ups. Two months later when the submitter has had enough, they go to FULL DISCLOSURE and the vendor gets pissed off and starts attacking the person who reported it for not giving them enough time to write a patch they haven't even started on. Then they spend another month making lousy excuses for why it's not a serious issue and half assed suggestions of what you can turn off to avoid the problem. Finally, after about four months of hand wringing, press releases, and general bullshit, you might get a patch. If you're lucky, it won't require you to start the process over again by introducing a brand new vulnerability. If you're lucky.

There's a huge difference here. The Linux folks jumped up and solved the problem. They didn't sit around pissing on their hands for months and making excuses like a lot of vendors do.

Re:There's a big difference...

[Allen Zadr]

A well patched system, Linux or Windows, doesn't need a firewall.

"WHAT YOU SAY!?"

I run a corporate network without a firewall. Every time a major issue comes around and destroys every freaking company around me, I go by with maybe two systems effected. Why? I stay up-to-date on all patches, and I keep relatively SANE security policies in place.

A firewall is a lot less necessary than firewall vendors would have you believe. My experience is that firewalls breed a false sense of security. Someone goes home over the weekend with a laptop - and comes back with a zombie virus/worm/etc. that goes and infects everything while the IT department is "taking their time" evaluating a security update for a month (I do 24 hour tests).

Why not firewall, is the other thing I hear. Mostly, it's so that every one of my systems can be an internet service provider. That's what the internet is about. Enabling users to say, hey - I've got that file right here on my local FTP, come get it. Here, log onto my VNC desktop, and I'll show you.

Firewalls create industries like WebEx. Because technology has come from 'wow, I didn't know you could do that,' to, 'I didn't know you could do that because I'm firewalled.'

Finally, "It doesn't happen very often," quite clearly means that it has happened. Call it pre-teen style bitching if you will, but a lawsuit should have never been threatened (AFAIK, a lawsuit never actually went to court). Is someone finds a vulnerability, full disclosure should not be the only method to have Microsoft take you seriously. My teen years are LONG behind me, maybe I'm just sick of having to deal with Microsoft's crap since Windows for Workgroups 3.11 (when the problems started for me).

Re:There's a big difference...

[Minwee]

Of course you realise that by doing that you are violating several patents on "Air Gap Firewall Technology".

Re:There's a big difference...

[Anonymous Coward]

Now, if you are at a COMPANY and your system goes unpatched it's because the IT department there either doesn't believe the possible threat or does NOT care.

dont play that game... 3 months before the big nasty worm that hit I was threatened with being fired because I patched all my systems with thew RPC hole patch... Not by my supervisor but by a bunch of jerks in corperate IT... after it hit and we were immune to the problems, did I hear an "I'm sorry?" or anything else? nope.. my boss bought me lunch that entire week and wrote a shining/gleaming letter to be put in my employment file... but corperate asshats refused to acknowlege that a nobody from the midwest division knew more than them.

Most of the problems in companies that got nailed with the RPC hole worms was ignorance and apathy.. they do things "their way" and ignore anyone below them on the totem pole.. until the fire starts raging...

My boss and many of us are starting to change corperate IT by throwing them under the bus at every chance.... It's the only solution we can see to fix the problem.

Re:There's a big difference...

[johnnyb]

I think that's because automatically patching is not the solution either. The problem is that many computer users want "easy" solutions to difficult problems. They would rather take an easy road that claims to work rather than one that actually solves the problem.

My Dad is a perfect case-in-point. He's an upper-level manager of a company. He was telling me about a piece of software he was planning on purchasing. I asked him about security. His answer was, simply, that the salesperson said it was secure.

There's two things wrong with this:

1) He took the salesperson's word. In previous generations, people's words meant something. Trying to train them to think skeptically is difficult. In addition, by what yardstick would he, a non-technical manager, measure security? What's worse is that I've met his IT staff, and I wouldn't trust them to measure security, either.

2) He thinks that security is a yes/no option. Security is nothing like that. If someone were to be honest with him, and tell him that nothing is truely secure and it's all trade-offs, and then explain the trade-offs of their particular product, I'm sure he would have thought they were weaseling, when in fact they were telling the truth.

Re:There's a big difference...

[zsau]

Didn't work for me. I just get a white screen in the middle of the command prompt with a purple border that says in purple 0: PING 192.168.0.7. Pressing Enter runs ping a couple times.

I'm far from a Windows fanboy. I use Linux almost all the time... I just happened to have a Windows box on my network atm.

Re:There's a big difference...

[maximilln]

2) He thinks that security is a yes/no option. Security is nothing like that. If someone were to be honest with him, and tell him that nothing is truely secure and it's all trade-offs, and then explain the trade-offs of their particular product, I'm sure he would have thought they were weaseling, when in fact they were telling the truth.

AMEN!

It's a problem that I run into quite often and not just with security. When you come to understand a topic intimately enough you learn that there is very little in the world that's a yes/no option. Everything requires a level of expertise and must be tailored to the specific task at hand. The issue is that the people requesting the services don't know, don't have time to learn, and don't want to learn. They want the yes/no answer to keep their life easy. If you're the person attempting to sell your services in order to keep food on the plate, however, you're faced with a dilemma: Say "yes" and possibly get mired in a situation which is impossible (secure a network full of users who are actively trying to break the network), or say "no" and don't get the job.

Re:There's a big difference...

[Odin's Raven]

I've come up with the final word in firewall technology. What I do is connect my PC to the DSL router with a 10' ethernet cable. Then, using an approved tool, I carefully cut the cable, making sure to sever it completely.

This is a common mistake that many first-time security administrators make. You're supposed to cut the cable before making the PC/router connection -- always implement your security protocol before connecting equipment to the outside world.

What we really need is an article suggesting how I can speed up my downloads...

Your downloads are probably slow because your machine was compromised during the time when your security was down - i.e., the interval between connecting the unsecured cable and the time you properly locked the connection down. Slow downloads are a key sign of a compromised system.

Once you suspect your machine's been compromised, there's really no safe solution other than reinstalling everything from scratch. I'd also suggest discarding the cable and getting a new one - since you didn't secure the cable first, there may be an RF resonance bug lurking on the PC half of the cable, waiting to reinfect your machine when you hook it back up.

You're obviously new to this, so just in case you haven't heard about them - RF resonance bugs use the reflection characteristics of an Ethernet cable to create a self-reinforcing standing-wave signal containing a copy of the virus. Older versions of these bugs could be dealt with simply by putting the cable in a Faraday cage and grounding the cable. But several of the more current RF resonator bugs contain quantum-mechanical sideband waveforms - put one of those in a Faraday cage and the q-m sidebands can refractively propogate into the cage itself, and you'll spend the rest of the day chasing down heisenbugs.

Anyways, don't feel bad about this - it's a common enough mistake when you're just getting started with security. And by posting on /. you may have helped several other novices avoid making the same mistake.

Windows is obviously superior

[Athas]

It doesn't require external programs in order to crash.

The best way to avoid this bug

[foidulus]

is to buy a mac and run yellow dog on it!

/ducks

Re:The best way to avoid this bug

[TheRaven64]

The question is not when it will be modded down, but who will do the modding. Will it be:

1. Linux zealots moderating it down because it suggests that you buy a Mac, or
2. Mac zealots moderating it down because it suggests you don't use OS X?

Gentlemen, place your bets now.

Wait,

[Anonymous Coward]

you want us to "read" the article and not jump headfirst into an open source vs. closed source flamewar??? :P

In case of slashdotting

[Anonymous Coward]

#include <stdio.h>

int main(void)
{
printf("I love Windows\n");
return (0);
}

This is another reason why C should be deprecated

[Anonymous Coward]

Gentlemen, the time has come for a serious discussion on whether or not to continue using C for serious programming projects. As I will explain, I feel that C needs to be retired, much the same way that Fortran, Cobol and Perl have been. Furthermore, allow me to be so bold as to suggest a superior replacement to this outdated language.

To give you a little background on this subject, I was recently asked to develop a client/server project on a Unix platform for a Fortune 500 company. While I've never coded in C before I have coded in VB for fifteen years, and in Java for over ten, I was stunned to see how poorly C fared compared to these two, more low-level languages.

C's biggest difficulty, as we all know, is the fact that it is by far one of the slowest languages in existance, especially when compared to more modern languages such as Java and C#. Although the reasons for this are varied, the main reasons seems to be the way C requires a programmer to laboriously work with chunks of memory.

Requiring a programmer to manipulate blocks of memory is a tedious way to program. This was satisfactory back in the early days of coding, but then again, so were punchcards. By using what are called "pointers" a C programmer is basically requiring the computer to do three sets of work rather than one. The first time requires the computer to duplicate whatever is stored in the memory space "pointed to" by the pointer. The second time requires it to perform the needed operation on this space. Finally the computer must delete the duplicate set and set the values of the original accordingly.

Clearly this is a horrendous use of resources and the chief reason why C is so slow. When one looks at a more modern (and a more serious) programming language like Java, C# or - even better - Visual Basic that lacks such archaic coding styles, one will also note a serious speed increase over C.

So what does this mean for the programming community? I think clearly that C needs to be abandonded. There are two candidates that would be a suitable replacement for it. Those are Java and Visual Basic.

Having programmed in both for many years, I believe that VB has the edge. Not only is it slightly faster than Java its also much easier to code in. I found C to be confusing, frightening and intimidating with its non-GUI-based coding style. Furthermore, I like to see the source code of the projects I work with. Java's source seems to be under the monopolistic thumb of Sun much the way that GCC is obscured from us by the marketing people at the FSF. Microsoft's "shared source" under which Visual Basic is released definately seems to be the most fair and reasonable of all the licenses in existance, with none of the harsh restrictions of the BSD license. It also lacks the GPLs requirement that anything coded with its tools becomes property of the
FSF.

I hope to see a switch from C to VB very soon. I've already spoken with various luminaries in the C coding world and most are eager to begin to transition. Having just gotten off the phone with Mr. Alan Cox, I can say that he is quite thrilled with the speed increases that will occur when the Linux kernel is completely rewritten in Visual
Basic. Richard Stallman plans to support this, and hopes that the great Swede himself, Linux Torvaldis, won't object to renaming Linux to VB/Linux. Although not a C coder himself, I'm told that Slashdot's very own Admiral Taco will support this on his web site. Finally,
Dennis Ritchie is excited about the switch!

Thank you for your time. Happy coding.

Re:Open Source Community shows its Value

[Anonymous Coward]

It shouldn't be long before a patch is issued to resolve this problem. Thank goodness for caffene loving geeks everywhere!

Let's just hope they're not browsing for pr0n.

if you're running 2.4.25 or 2.4.26

[Anonymous Coward]

here's a direct link to the patch.

not whoring. ;)

The problem appears to be...

[Ayanami Rei]

... that if you trigger a floating point exception inside a signal handler (specifically SIGALRM), the kernel doesn't handle it correctly, hanging the system. It appears to affect both SMP and UP kernels.

Some questions I have to those who may have been following this:

Does the crash occur without the syscalls in the signal handler/main process?
Does the crash occur on SMP machines?
Does the crash occur with other signals (PIPE, USR1, etc.)
Does the crash occur on ppc, sparc, etc?

Who has shell access?

[slusich]

How many systems deployed in real world enviorments give anyone other then IT staff shell access?

Re:Who has shell access?

[Welsh Dwarf]

Sourceforge?

Re:Who has shell access?

[mattyrobinson69]

How about these?

I used the search term "shell accounts", incase you couldn't think of something more relevant than "cheese" or "striped cow" to search for....

Re: My Experience with the Linux

[timotten]

...having programmed in VB for the last 8 years doing kernel level programming...

I think you'll need to clarify that for us slashdot folk.

Re:OS bugs are like golf...

[RAMMS EIN]

Well, those who have been paying attention know that Linux has had quite a few (read: way too many) critical bugs in the past year. Most of them were related to do_mremap (how many times do they have to "fix" that until its fixed?!), varying in severeness from DoS to local root exploits. How many has the Windows kernel had in the last 12 months? I am afraid that this comparison might fall out to the advantage of Windows. Until you take into account time to fix, maybe. Off to patch my systems...

Okay, I'm confused...

[ThePatrioticFuck]

I thought Monday's were supposed to be Windows patch days, Tuesdays were for Linux, Wednesday was Apache, Thursday was Windows again, Friday was SSH...

I read the article too, I'm an idiot.

[Ayanami Rei]

The article says it affects x86 (and x86-64) only.

So itanium, ppc, etc. are safe. But my other questions still remain.

Note that the person who reported the bug thought they were triggering a gcc bug. As it turns out, he munged his FPU assembly instructions.
The GCC people rightly told him to contact the lkml... it's definitely an exception handling issue.

You know you have problems if...

[ulmanms]

Your sysadmin needs this advice:
If your system is a production server with 1000 on line users then do not test this code on that box.

Re:OS bugs are like golf...

[martingunnarsson]

Slashdot blurb about Windows bug
Linux trolls: Windows sucks!!!

Slashdot blurb about Linux bug
Linux trolls: Windows sucks!!!

I know plenty who do...

[Allen Zadr]

I know plenty of users who do care...

In the real world, where I work, I run a Hybrid network where I'm still waiting for Windows XP Service Pack 2 to come out in a finalized form because I don't have an option to pull just the parts that I need, and SP2 RC2 is not quite ready to unleash on my network (although I have actively TESTED it). Of course, this just fixes some vulnerabilities that have existed for over a year.

Don't tell me that I, as a Windows User and Administrator, don't care. While I've ignored this kernel issue over the weekend, I get to actively compile come kernel patches and test those. I'll bet, even before my testing, that I'll be able to have a production solution by tomorrow. Even if SP2 releases this afternoon, I'll still have to test it before deployment, so the Linux solution will be in production first.

Vulnerability in Linux, NetBSD Unaffected!!!

[RAMMS EIN]

FTFA (From The Fine Article):

``This doesn't affect NetBSD Stable.''

The exploit code also doesn't work on Windows 95, nor on Menuet. I haven't tested SkyOS, because I don't have a license.

Re:Vulnerability in Linux, NetBSD Unaffected!!!

[Senjutsu]

Officials say that, at this time, they are unsure whether or not the Amiga is affected. Precaution is urged.

Re:Fixed quickly.

[kaiidth]

Patch is here on LKML. And of course it is on the original exploit page too.

Here is the LKML discussion thread on the subject. It's an interesting bug, briefly summarised by Matt Mackall as follows:

The example code's bogus
asm is generating an FPU fault in frstor in its signal handler, that's
bumping us into math_error -> force_sig_info ->
specific_send_sig_info. Then we hit:

if (LEGACY_QUEUE(&t->pending, sig))

which decides we don't need to send the signal after all and we bail
all the way back out and recurse.

So there's a bit of a massive problem with FPU exception handling, which didn't come to light before. Wheee. Fun.

UML?

[spacefrog]

Very vital question for the UML virtual server leasing cottage industry and the customers of same.

If this were to be run on a UML session, what would happen? Would the damage be limited to that UML session, or would the host machine go down?

Re:UML?

[bluelip]

Talked about on the mailing lists.

http://marc.theaimsgroup.com/?l=linux-kernel&m=1 08 695598318818&w=2

Says session just dies. Host is OK.

I think we're forgetting one important thing....

[kalirion]

How do we blame Micro$oft for this?

Know what else

[Anonymous Coward]

As for this bug, don't start bashing Linux left and right. Linux isn't perfect, no software is. But unlike when there is a bug in windows a fix is on the way as fast as possible. In fact, there is a patch on the site right now! And for you zealots who say stuff like "No big deal, who is going to do that? No the kind of person you give shell access to." shut up. Admit that Linux is not the perfection in computing.

You know what else makes the kernel crash? At least if you are using 2.6.5 or higher if you enable APIC/APIC-IO and you have an nforce chipset the system will lock up as soon as you do too much I/O.

Windows Community

[Allen Zadr]

WinDrivers.com - is very much a Windows community site (there are others as well). Most Windows admins I know belong to this site. There are forums there, but there's not so much flame-wars about design (something they have no control over), but there are wars over the best default security settings to leave lUsers with, etc.

It's good reading for anybody interested, however, unlike slashdot, registration is required.

Re:Fixed quickly.

[kaiidth]

Mind you, at the risk of replying to myself it is worth noting that the patch currently available actually does nothing more meaningful than checking to see if the code that got you there is this exact exploit or not... so I would expect a better patch to be coming out that actually deals with the real problem, which appears to be that some poor munchkin started to write an FPU exception handler somewhere near version 2.3 and got distracted before finishing it. I assume though that the production of such a patch implies working out what the dude actually meant to do, first.

IGNORE above ... new info.

[Ayanami Rei]

God I wish I could edit posts.

The issue isn't that the context is gone... the issue is that the kernel is executing a non-waiting FPU instruction i.e. "fwait" on returning from the a context that flushes a user thread (i.e. return from signal handler, syscall after execve). Triggers the FPE, except the kernel isn't set up to handle FPEs properly from kernel space in this case. The problem is that the TS flag is set because it's switching tasks, so it receives a different exception, trap 7 (device_not_available). The purpose of that exception is to signal the kernel that a newly created process wants the FPU. So it attempts to set up the FPU... which ends up calling __clear_fpu again... heh... and the original exception isn't cleared yet... whoops.

What's really weird is I found this document, which details the potential problems of trying to use the FPU in a interrupt handler in the Linux kernel.

They brought up the potential of triggering this EXACT PROBLEM... quote "endless trap 7 activation"... only in this case they're talking about writing an interrupt routine, not returning from a signal handler. Still, they already discovered this misbehavior...

Well, you can't really call it that, though. It's was sort of by design (to make task switching faster). But the thing is you have to be ABSOLUTELY SURE that you never raise an FPE when TS is set, and you're NOT a user thread. That's what gets you burned here.

Patch doesn't work for me, 2.4.26

[TDot]

I have a "very nearly vanilla" 2.4.26 kernel - all that's patched are some netfilter things for more targets. This patch didn't work for me - the patch went fine (my signal.c is no different from vanilla), and the resulting kernel booted fine, but the exploit still crashed my box. I'm using gcc-2.95.4 , Debian 3.0 (Woody). No I didn't forget to run lilo or whatever (i'm using Grub). Any ideas?

What does the patch fix?

[Urban Garlic]

Question for the kernel gurus out there -- I read the article and the patch (so sue me), and it seems to me that the patch just redirects the signal-handler flow if sig==8.

This may well protect against the example exploit, but what happens if you get a floating-point exception in the handler for some other signal?

The provided patch does not look like a real fix, unless the deeper bug really does just involve sig==8.

Re:A good time to disable compiler access

[PoochieReds]

This does no good if someone builds the program on another machine and then copies it to your host. Limiting compiler access really doesn't help secure anything unless you also prevent anyone from transferring any files to the machine (which is quite impractical).

Re:A good time to disable compiler access

[Sloppy]

Having a local compiler available makes things easier, but it doesn't give a user any fundamental powers that they wouldn't already have. They can get executable code into the system in other ways, even if they don't have a local compiler. Transfer it from another computer, or even manually enter it. Are you also going to disable cat and chmod?

I don't think this idea is useful.

Although Windows is Easier to apply patches to...

[koniosis]

The update may be avaliable faster than Windows, but you cannot say that it is /easier/ to apply than a Windows patch. I hate recompiling my kernel, it always takes me a number of attempts until everything works. Also my server is running Linux and is serving two houses of people with net access, I can't just take it down and mess around with it for hours while I have fun trying to get a working kernel. So regardless of when the patch was released I still need to wait until later tonight to apply the patch.

Re:This is the best they can come up with?

[BenjyD]

This is a reasonably serious bug. A well-configured *nix box should not be crashable by anything a normal user can do. The amount of memory a user can allocate, the number of processes they can launch, the size and number of files they can create should all be limited through user limits. There is no way (AFICS) to prevent this bug being exploited through those kind of limits. If there are lots of people logged in, figuring out who crashed the box would be quite hard - just have the crashing program delete itself before it crashes the box.

Hitting ctrl-alt-delete or the power requires physical access, which shell users almost never have (I don't even know where most of the computers I use every day are - they could be in Timbuktu for all I care).

FYI suse 9.1 not vulnerable

[sloanster]

Granted, this crashme program, which requires local shell access, does seem to work in some cases.

However, it does not do so on suse linux 9.1 - it creates an unkillable process, but the system continues to run normally.

another way to fix the problem...

[naken]

#include
#include
#include

static void Handler(int ignore)
{
char fpubuf[108]; // __asm__ __volatile__ ("fsave %0\n" : : "m"(fpubuf));
write(2, "*", 1); // __asm__ __volatile__ ("frstor %0\n" : : "m"(fpubuf));
}

int main(int argc, char *argv[])
{
struct itimerval spec;
signal(SIGALRM, Handler);
spec.it_interval.tv_sec=0;
spec.it_interval.tv_usec=100;
spec.it_value.tv_sec=0;
spec.it_value.tv_usec=100;
setitimer(ITIMER_REAL, &spec, NULL);
while(1)
write(1, ".", 1);

return 0;
}

by simply commenting out the inline assembly, i fixed crash.c so it can no longer crash Linux!

1 2 1 2 THE NAKEN CREW

THIS is why I hate Linux

[gosand]

This is precisely why I hate Linux so much. When I read about Windows vulnerabilities, it is something easy like "Port 1234 left wide open" or "Outlook will email everyone in the world with your penis size if you launch IE." I can comprehend those bugs. When a Linux exploit is discovered, it is all "SIGALRM this" and "__jiggawhat_ that".

How am I supposed to keep up with this stuff?

[CORRECTION] Re:RHEL3 doesn't crash

[photon317]

My test was on a dual P4 (hyperthreading). Running a single instance of the code only locked a single cpu. I just played with it again, and running 4 instances locked the box. So RHEL3 is vulnerable, and a correct description of the problem is that the exploit locks up 1 cpu in an endless loop that cannot be stopped. For systems with multiple CPUs, you have to do this once for each cpu (twice for each physical cpu if hyperthreading) in order to lock the whole box up.

this *is* a big deal

[sentientbrendan]

The *first* post I see is some bullshit lauding the superiority of the opensource development process with this as an example. RTFA. Here is some sensible info and advice.

1. There *was no patch*. Some systems were immune, but that was completely by chance.
2. There is a patch *now*, but the article also says people are already using the thing to crash free shell providers on day 0.
3. The patch, at this point, requires a kernel recompile. Not everyone running linux knows how to do that. Many who do are too lazy. Don't give me some shit about how everyone running linux is so 1337 that they will be sure the have already patched their system. I know you. You aren't that 1337.
4. Yes, this *is* a big deal. We were caught with our pants down, plain and simple. This *is* worse than any windows security issue that has come up in a long time.
5. Please *do* compile the demo code against your system and test it. If your system crashes, please patch. Don't act like many and just ignore this, especially if you are running a server or anything that stays connected for any amount of time. It also might be a good idea to turn off your telnet and ssh daemon (yes, even ssh) until you patch.
6. If you are *not* running linux or not running on x86, it might also be a good idea to test the demo code against your system. If you are running windows, some versions of windows *do* support possix to a limited degree. The code *might* compile. Then there is also, cygwin. This is probably a bug specific to linux x86, but it won't hurt to check.