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AFAICT this is graded "Don't Panic".http://seclists.org/oss-sec/2014/q1/187 says it affects only x32 -- which is that weird hybrid 32-bit address space with AMD64 instructions that nobody uses. Especially not Slackware. The vuln goes back to 3.4, because 3.4 is when x32 was merged...
Edit: Wrong wrong wrong! see metaschima's post below.
Last edited by 55020; 01-31-2014 at 01:51 PM.
Reason: Fessed up to wrongness, and added strikethrough ;-)
Hi mancha, a new serious kernel bug (CVE-2014-0038) affecting _all_ versions since 3.4. Second patch seems the correct and was merged here.
I was just about to post this. It really does look serious and x32 is enabled in slackware64 kernels.
Luckily I have a custom kernel that is pure 64-bit.
EDIT:
It looks like slackware64 glibc is NOT built with x32 support. So I guess maybe it isn't so bad after all. The user would have to build glibc with x32 support and then run a compromised x32 program.
Last edited by metaschima; 01-31-2014 at 01:27 PM.
Eek! Thanks! You're right: CONFIG_X86_X32=y
I hereby withdraw that "Don't Panic" grading. Sorry!
Ah, but CONFIG_X86_X32_ABI is not set. Apparently ld isn't handling x86_32 properly, so the kernel didn't enable that option. Accidentally not vulnerable.
Since I'm here, in cases like the pixman/X server trapazoid bug which can lead to a crash but not privilege escalation, I'm inclined to look at it as a bug rather than a security issue even though it was assigned a CVE. It's not in the same realm as something like the libXfont overflow.
Ah, but CONFIG_X86_X32_ABI is not set. Apparently ld isn't handling x86_32 properly, so the kernel didn't enable that option. Accidentally not vulnerable.
Hi Pat. I believe Slackware64 14.1 & current are vulnerable (see my oops in the post just above yours).
CONFIG_X86_X32_ABI is a compile-time option which is set after confirming ld can emulate elf32_x86_64.
You can check Slack's ld supported emulations with:
Let that run a bit and see if the option is being set (-DCONFIG_X86_X32_ABI).
--mancha
Ah, I see. It is there at compile time, but not in the .config.
Is there actually any interest in x86_x32? If the toolchain doesn't fully support it and nobody's using it for anything, perhaps the path of least resistance would be to turn off CONFIG_X86_X32 in the kernel entirely.
Full use of x32 requires x32 glibc, gcc, gdb, and ld (binutils). If these are not provided (and they are not), then there is no reason to enable x32 in the kernel. https://sites.google.com/site/x32abi/
The proof of concept by mancha doesn't use glibc, but rather assembly ... which is clever.
Is there actually any interest in x86_x32? If the toolchain doesn't fully support it and nobody's using it for anything, perhaps the path of least resistance would be to turn off CONFIG_X86_X32 in the kernel entirely.
The API never really took off so my hunch is very few, if any, will notice if you remove it. Then again, no one misses the water till the well runs dry.
Quote:
Originally Posted by volkerdi
Since I'm here, in cases like the pixman/X server trapazoid bug which can lead to a crash but not privilege escalation, I'm inclined to look at it as a bug rather than a security issue even though it was assigned a CVE.
The pixman vulnerability seems limited to denial of service. I'm not familiar with the EXA acceleration code in xorg-server so without code review I have no idea if there's potential to leverage the wraparound for things like code execution. To be honest I didn't dwell on it. X runs as root; the fix is trivial; why risk it?
ALERT: CVE-2014-0038 is no longer merely theoretical. A working Ubuntu exploit was made public by Rebel. I can confirm
the exploit methodology does work on Slackware64 14.1+.
Given the exposure, I authored a kernel module which protects against this attack and which I now share with the Slackware
community.
To get it working, as root do:
Code:
# tar xf nox32recvmmsg.tar.bz2
# cd nox32recvmmsg
# make
# insmod nox32recvmmsg.ko
--mancha
EDIT: The kernel module has undergone two revisions since the original post. See follow-up posts for more info.
Make sure the tarball you downloaded is the most recent. Compare to hash:
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