CVE-2021-47491: mm: khugepaged: skip huge page collapse for special files

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: 2024-05-22 · updated 2026-06-17

Description

In the Linux kernel, the following vulnerability has been resolved: mm: khugepaged: skip huge page collapse for special files The read-only THP for filesystems will collapse THP for files opened readonly and mapped with VM_EXEC. The intended usecase is to avoid TLB misses for large text segments. But it doesn't restrict the file types so a THP could be collapsed for a non-regular file, for example, block device, if it is opened readonly and mapped with EXEC permission. This may cause bugs, like [1] and [2]. This is definitely not the intended usecase, so just collapse THP for regular files in order to close the attack surface. [shy828301@gmail.com: fix vm_file check [3]]

Affected products

Linux kernel: from 5.4 before 5.10.78; from 5.11 before 5.14.16; 5.15-rc1, 5.15-rc2, 5.15-rc3, 5.15-rc4, 5.15-rc5, 5.15-rc6 (+1) — fixed in 5.10.78, 5.14.16

How to fix

Upgrade to a fixed version: Linux kernel 5.10.78, 5.14.16. Check the vendor advisory for mitigations.

References

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