# CVE-2026-93227: mm/mm_init: deferred_grow_zone(): fix out-of-range first_deferred_pfn

> A kernel panic occurs during boot when deferred struct page initialization overflows due to specific CMA configurations, causing a denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-93227, DEBIAN-CVE-2026-93227, GHSA-x6mv-65qg-c346, UBUNTU-CVE-2026-93227

## What is CVE-2026-93227?

CVE-2026-93227 is a denial of service vulnerability in Linux, published on 24 Sep 2026. 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:

mm/mm_init: deferred_grow_zone(): fix out-of-range first_deferred_pfn

With CONFIG_DEFERRED_STRUCT_PAGE_INIT enabled, deferred_grow_zone()
initializes struct pages early in boot to satisfy an allocation.

With a large CMA reservation in place, the ranges deferred_init_memmap()
finds may not add up to the allocation it was asked for, and the function
ends up initializing the memory map of the entire zone and still falls
short.

That is fine in itself: the function accounts for it and leaves the
caller to decide whether it now has enough memory.

However, the update of pgdat->first_deferred_pfn that tracks where
uninitialized memory map starts could overflow.

If the node's RAM end is not aligned on PAGES_PER_SECTION boundaries and
some deferred struct pages were initialized, pgdat->first_deferred_pfn
would point past the end of the node's memory.

deferred_init_memmap() later picks up from pgdat->first_deferred_pfn and
hits a BUG_ON(), because it expects a pfn within its node.

For example, when running a kernel with CONFIG_DEFERRED_STRUCT_PAGE_INIT=y
and CONFIG_CMA=y using the following qemu command line

  qemu-system-x86_64 -enable-kvm -m 8032M -kernel bzImage \
      -append "nokaslr cma=4768M@0x100000000"

the kernel panics:

  kernel BUG at mm/mm_init.c:2131!
  CPU: 3 UID: 0 PID: 36 Comm: pgdatinit0 Not tainted 7.2.0-rc6 #1
  RIP: 0010:deferred_init_memmap+0x1b8/0x1c0
  RAX: 0000000000236000 R13: 0000000000238000
  Call Trace:
   kthread+0xdf/0x120
   ret_from_fork+0x187/0x250

Make sure that the update of pgdta->first_deferred_pfn does not overflow
when the entire zone's (and therefore node's) memory map is initialized.

[rppt: massaged the changelog]

## Which versions are affected by CVE-2026-93227?


## How do I fix CVE-2026-93227?

Apply the vendor's patch.

## Is CVE-2026-93227 being exploited?

There is no known exploitation of CVE-2026-93227 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93227 and fix it if it is affected.

What it is: CVE-2026-93227 is a denial of service vulnerability in Linux, published on 24 Sep 2026. 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-2026-93227 in the wild and no public exploit code.

Affected product: Linux. 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-2026-93227/ (Markdown: https://insights.sbomify.com/CVE-2026-93227/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93227
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93227
- OSV: https://osv.dev/vulnerability/CVE-2026-93227

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93227/
Summaries are generated and may contain mistakes; the official description above is the record.