CVE-2024-49885: mm, slub: avoid zeroing kmalloc redzone
In the Linux kernel, the following vulnerability has been resolved:
mm, slub: avoid zeroing kmalloc redzone
Since commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated kmalloc space than requested"), setting origsize treats the wasted space (objectsize - origsize) as a redzone. However with initonfree=1 we clear the full object->size, including the redzone.
Additionally we clear the object metadata, including the stored origsize, making it zero, which makes checkobject() treat the whole object as a redzone.
These issues lead to the following BUG report with "slubdebug=FUZ initonfree=1":
[ 0.000000] ============================================================================= [ 0.000000] BUG kmalloc-8 (Not tainted): kmalloc Redzone overwritten [ 0.000000] ----------------------------------------------------------------------------- [ 0.000000] [ 0.000000] 0xffff000010032858-0xffff00001003285f @offset=2136. First byte 0x0 instead of 0xcc [ 0.000000] FIX kmalloc-8: Restoring kmalloc Redzone 0xffff000010032858-0xffff00001003285f=0xcc [ 0.000000] Slab 0xfffffdffc0400c80 objects=36 used=23 fp=0xffff000010032a18 flags=0x3fffe0000000200(workingset|node=0|zone=0|lastcpupid=0x1ffff) [ 0.000000] Object 0xffff000010032858 @offset=2136 fp=0xffff0000100328c8 [ 0.000000] [ 0.000000] Redzone ffff000010032850: cc cc cc cc cc cc cc cc ........ [ 0.000000] Object ffff000010032858: cc cc cc cc cc cc cc cc ........ [ 0.000000] Redzone ffff000010032860: cc cc cc cc cc cc cc cc ........ [ 0.000000] Padding ffff0000100328b4: 00 00 00 00 00 00 00 00 00 00 00 00 ............ [ 0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.11.0-rc3-next-20240814-00004-g61844c55c3f4 #144 [ 0.000000] Hardware name: NXP i.MX95 19X19 board (DT) [ 0.000000] Call trace: [ 0.000000] dumpbacktrace+0x90/0xe8 [ 0.000000] showstack+0x18/0x24 [ 0.000000] dumpstacklvl+0x74/0x8c [ 0.000000] dumpstack+0x18/0x24 [ 0.000000] printtrailer+0x150/0x218 [ 0.000000] checkobject+0xe4/0x454 [ 0.000000] freetopartiallist+0x2f8/0x5ec
To address the issue, use origsize to clear the used area. And restore the value of origsize after clear the remaining area.
When CONFIGSLUBDEBUG not defined, (getorigsize()' directly returns s->objectsize. So when using memset to init the area, the size can simply be origsize, as origsize returns objectsize when CONFIGSLUBDEBUG not enabled. And origsize can never be bigger than objectsize.
Other sources
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— Launchpad
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2024-49885?
CVE-2024-49885 has not been assigned a specific CVSS score but is associated with memory management issues in the Linux kernel.
How do I fix CVE-2024-49885?
To address CVE-2024-49885, update your Linux kernel to a version that includes the fix, such as 5.10.223-1, 6.1.123-1, or later versions.
Which Linux kernel versions are affected by CVE-2024-49885?
CVE-2024-49885 affects Linux kernel versions from 6.2 to 6.10.14 and 6.11 to 6.11.3.
Is CVE-2024-49885 a remote vulnerability?
CVE-2024-49885 is not categorized as a remote vulnerability but involves local memory management that could be exploited.
What types of systems may be impacted by CVE-2024-49885?
Systems using affected versions of the Linux kernel, including various Linux distributions, could be impacted by CVE-2024-49885.