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 nodes 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 nodes 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 zones (and therefore nodes) memory map is initialized.

[rppt: massaged the changelog]

Affected Software

References

• https://git.kernel.org/stable/c/45489d4f95802903ab35799b400b346fa4e13151
• https://git.kernel.org/stable/c/84339578c2d6936ac3a93cd1f0bbaa3468a988f2
• https://git.kernel.org/stable/c/97090500d776c3f6d08e857e3a0a7cf092999094