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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-93227 being exploited?
There is no known exploitation of CVE-2026-93227 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-93227, DEBIAN-CVE-2026-93227, GHSA-x6mv-65qg-c346, UBUNTU-CVE-2026-93227.