# CVE-2022-49778: arm64/mm: fix incorrect file_map_count for non-leaf pmd/pud

> A bug in the Linux kernel arm64 memory management causes a kernel panic when collapsing huge pages, leading to a denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 May 2025
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2022-49778, GHSA-54j7-px5q-9wrr, UBUNTU-CVE-2022-49778

## What is CVE-2022-49778?

CVE-2022-49778 is a medium-severity denial of service vulnerability in Linux kernel, published on 1 May 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

arm64/mm: fix incorrect file_map_count for non-leaf pmd/pud

The page table check trigger BUG_ON() unexpectedly when collapse hugepage:

 ------------[ cut here ]------------
 kernel BUG at mm/page_table_check.c:82!
 Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
 Dumping ftrace buffer:
    (ftrace buffer empty)
 Modules linked in:
 CPU: 6 PID: 68 Comm: khugepaged Not tainted 6.1.0-rc3+ #750
 Hardware name: linux,dummy-virt (DT)
 pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
 pc : page_table_check_clear.isra.0+0x258/0x3f0
 lr : page_table_check_clear.isra.0+0x240/0x3f0
[...]
 Call trace:
  page_table_check_clear.isra.0+0x258/0x3f0
  __page_table_check_pmd_clear+0xbc/0x108
  pmdp_collapse_flush+0xb0/0x160
  collapse_huge_page+0xa08/0x1080
  hpage_collapse_scan_pmd+0xf30/0x1590
  khugepaged_scan_mm_slot.constprop.0+0x52c/0xac8
  khugepaged+0x338/0x518
  kthread+0x278/0x2f8
  ret_from_fork+0x10/0x20
[...]

Since pmd_user_accessible_page() doesn't check if a pmd is leaf, it
decrease file_map_count for a non-leaf pmd comes from collapse_huge_page().
and so trigger BUG_ON() unexpectedly.

Fix this problem by using pmd_leaf() insteal of pmd_present() in
pmd_user_accessible_page(). Moreover, use pud_leaf() for
pud_user_accessible_page() too.

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2022-49778?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2022-49778?

Apply the vendor's patch.

## Is CVE-2022-49778 being exploited?

There is no known exploitation of CVE-2022-49778 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2022-49778 and fix it if it is affected.

What it is: CVE-2022-49778 is a medium-severity denial of service vulnerability in Linux kernel, published on 1 May 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2022-49778 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2022-49778/ (Markdown: https://insights.sbomify.com/CVE-2022-49778/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2022-49778
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2022-49778
- OSV: https://osv.dev/vulnerability/CVE-2022-49778

---
From sbomify Insights: https://insights.sbomify.com/CVE-2022-49778/
Summaries are generated and may contain mistakes; the official description above is the record.