CVE-2024-46838: userfaultfd: don't BUG_ON() if khugepaged yanks our page table

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-09-27 · updated 2026-06-17

Description

In the Linux kernel, the following vulnerability has been resolved: userfaultfd: don't BUG_ON() if khugepaged yanks our page table Since khugepaged was changed to allow retracting page tables in file mappings without holding the mmap lock, these BUG_ON()s are wrong - get rid of them. We could also remove the preceding "if (unlikely(...))" block, but then we could reach pte_offset_map_lock() with transhuge pages not just for file mappings but also for anonymous mappings - which would probably be fine but I think is not necessarily expected.

Affected products

Linux kernel: from 6.6 before 6.6.51; from 6.7 before 6.10.10; 6.11-rc1, 6.11-rc2, 6.11-rc3, 6.11-rc4, 6.11-rc5, 6.11-rc6 — fixed in 6.10.10, 6.6.51

How to fix

Upgrade to a fixed version: Linux kernel 6.10.10, 6.6.51. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2024-46838 or the next vulnerability affects your stack