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Root Privileges Through Linux Kernel Bug
Lars T. writes "The H has a story about a Linux kernel bug that allows root level access. 'According to a report written by Rafal Wojtczuk (PDF), a conceptual problem in the memory management area of Linux allows local attackers to execute code at root level. The Linux issue is caused by potential overlaps between the memory areas of the stack and shared memory segments.' SUSE maintainer Andrea Arcangeli provided a fix for the problem in September 2004, but for unknown reasons this fix was not included in the Linux kernel. The bug is not related to the X Server bug found by Brad Spengler."
As the linked article notes: "SUSE itself has the fix and SUSE Linux Enterprise 9, 10 and 11 as well as openSUSE 11.1 through 11.3 do not exhibit this vulnerability."
How can the two bugs be unrelated? both articles have the exact same link to the exact same PDF! (Hint: the pdf's filename is xorg-large-memory-attacks.pdf on both).
No, just that this particular bug has been patched in SUSE for six years, while mainline has only just gotten the fix.
cat:
From the RedHat bug report: Eugene Teo (Security Response) 2010-08-12 21:44:06 EDT Linus has committed a fix for this issue: http://git.kernel.org/linus/320b2b8de12698082609ebbc1a17165727f4c893
Indeed, 5 years old and no exploit. Patched several years ago by the distros. The question is why didn't it get back into the kernel tree.
Why not ask the kernel developers? Nah, I'm not just joking, don't ask those nutjobs anything, they'll just freak out and start yelling at you.
If I read the git patch correctly, if said root process has a memory-mapped page coincident with a non-root process, and the non-root process can write to said memory mapped region (via having it memory mapped into their own process), then said non-root process can affect the behavior of the root process.
What was broken, and appears to have been corrected, is that an application's *stack* could grow into a memory-mapped page and corrupt the data in the root process while it's at it. (The stack is a piece of memory that hold data about the functions currently executing in a particular thread in your program.)
(enter educated guess section; I spend most of my time coding userland apps on Windows, not Linux.)
The case where this seems most possible to exploit is the loading of shared libraries. I don't know if the same mmap mechanism is used by the kernel, though. While it's entirely probable that writing to that region is protected, so long as the application is doing so under its own memory privilege level, it's possible that there's a syscall into the kernel that expands a thread's stack when the allocated memory for that stack is nearly exhausted. The syscall's operations run with kernel privileges, and it looks like the stack page allocator wasn't sufficiently checking the properties of the userland address it was allocating stack into.
(end educated guess section; I'm probably wrong, anyway.)
tasks(723) drafts(105) languages(484) examples(29106)
No, normally access to the machine at user level should not imply access to the machine at root level.
The Tao of math: The numbers you can count are not the real numbers.
Why not ask the kernel developers? Nah, I'm not just joking, don't ask those nutjobs anything, they'll just freak out and start yelling at you.
I've seen many similar statements, so there may be some truth to this, but my experience is that they give you a short-as-possible only-most-relevant question such as "Can you bisect?" or reply like "Patch rejected: missing signoff". It appears their time is very valuable or they have to pay $5 pr. typed letter.
9/11: Never forget it was a false-flag operation
Actually, no, this is a simple Stack Buffer Overflow. Basically, by causing a running privileged process (e.g. X Server) to make a recursive call, the stack will grow into memory space owned by the unprivileged user. Now, all the unprivileged user has to do is put some code somewhere (perhaps by exploiting another buffer overflow) and rewrite the return address, which lives in its memory page.
The fix adds a guard page between the shared memory region and the system stack to protect against the stack growing into memory where it is no longer protected. At any rate, ProPolice would have prevented this mistake from being exploitable.
"Please describe the scientific nature of the 'whammy'" - Agent Scully
If it's a non-story then why did Linus patch it today? Apparently he didn't agree with your flippant way of looking at OS security.
I wonder how many bugs like this are lurking in closed source products, just waiting to be discovered and exploited?
I wonder how many bugs like this are lurking in open source projects, just waiting to be discovered and used against people that assume that the software they use is secure because they read Slashdot comments.
"I like to lick butts!" by MobileTatsu-NJG (#32700246) (Score:5, Informative)
What part of "local attackers" do you fail to understand?
Seven puppies were harmed during the making of this post.
At least we don't have to wait for four Tuesdays' time for the fix...
You're holding it wrong.
Sometimes people make mistakes.
Cut the guy a break, he's a Windows fanboy. He probably thinks a local user is just anyone in the same geographic region.
"When information is power, privacy is freedom" - Jah-Wren Ryel
Cut my post too short.
"SUSE maintainer Andrea Arcangeli provided a fix for the problem in September 2004, but for unknown reasons this fix was not included in the Linux kernel"
He's a troll, but that doesn't mean that there isn't a grain of truth to what he implies. Most Windows exploits are also technically local attacks, as are Trojans (by definition). Somebody thinking that they're safe (because the software runs with limited permissions) would be in for a nasty surprise if an attacker exploited this.
There's no place I could be, since I've found Serenity...
Indeed, 5 years old and no exploit.
How do you know?
Give me Classic Slashdot or give me death!
Behold the phenomenal power off Open Source! The time of each and every kernel developer is in fact a highly valuable commodity, yet I get the benefit of the fruits of their labor without shelling out a sixpence! And the best part? This was fixed last week.
Guns don't kill people; Physics kills people! - John Lithgow as Dick Solomon on Third Rock From The Sun
So I read the PDF...
which is the patch.. "Patch "mm: keep a guard page below a grow-down stack segment" has been added to the 2.6.32-stable tree"
and meanwhile my ubuntu update managaer pops up and shows an update for the kernel and gives the following link to the changelog...
http://launchpad.net/ubuntu/+source/linux/2.6.32-24.41/+changelog
Nice to see people are on the ball with security updates, even if it shouldn't have been happened in the first place.
Look at this graph: http://linuxinsecurity.blogspot.com/
Please do. Notice how the graphs show Windows with 10-12% of the issues unpatched?
That's the problem. Well that and the missing graph showing "time to patch"...
This sig intentionally left blank.
So, only 6 years late then? SuSE just went way up in my book.
I run: Windows, OS X, Linux, FreeBSD. Just because you have a hammer, doesn't mean everything is a nail.
a redundant first post...?
Yes, there was a redundant x in "h4xx0r5".
Compare this to Apple, which still hasn't fixed my Darwin kernel ring 0 exploit, which I reported in June.
It's x86-only, so no, it can't be used for the second step of an iPhone jailbreak. =(
"Screw Sun, cross-platform will never work. Let's move on and steal the Java language." - Visual J++ Product Manager
If you really want to get a fix in, the correct procedure is to keep pestering the maintainer for that area until they accept your patch. If you can't get them to accept it, you go up the chain.
Yes, in an ideal world all maintainers would be perfectly organized. In the real world things get lost, they get distracted, other issues pop up, and the patch doesn' t make it in.
If you care about it...make some noise.
This won't be a problem for me since I don't run Linux.
Now the shoe's on the other foot!
Yes, something is seriously wrong with this comparison. You compare a clean and unused operatingsystem with a fullfledged Linuxdistribution with a lot of applications.
Of course the Linuxdistribution will have more bugs, but you dont have to install all the software that comes with it. On the other hand, to be able to use the Windows server to something useful, you have to install more Microsoft and/or thirdparty software. It isnt even a webserver without installing more software in Secunias statistics. IIS has its own category.
Dont compare apples and pears, you will only fool yourself.