CVE-2026-93227

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]