CVE-2026-89604: efivarfs: Rate limit statfs() handler

CVE-2026-89604: efivarfs: Rate limit statfs() handler

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

efivarfs: Rate limit statfs() handler

Ravi reports that statfs() may be called by unprivileged users on the
efivarfs mount point, which may result in a flood of calls to the
QueryVariableInfo() runtime service. These calls are disproportionately
costly on x86 systems where the variable store is backed by SMM, as each
SMM entry requires a rendez-vous of all the CPUs.

So rate limit the calls to QueryVariableInfo() at twice per second, and
return the most recently obtained value for calls that are elided.

The Linux kernel CVE team has assigned CVE-2026-89604 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.5 with commit d86ff3333cb1d5f42d8898fb5fdb304e143c0237 and fixed in 6.12.109 with commit 8953bdd1b9c0e748d5408d3d0b8e7aeee5c9cd41
	Issue introduced in 6.5 with commit d86ff3333cb1d5f42d8898fb5fdb304e143c0237 and fixed in 6.18.50 with commit 92895a14329cc9533e2a74a265214f690ba3851a
	Issue introduced in 6.5 with commit d86ff3333cb1d5f42d8898fb5fdb304e143c0237 and fixed in 7.2.4 with commit 0dbc2e94b81df5a1264068b6ed3605c654b8afcb
	Issue introduced in 6.5 with commit d86ff3333cb1d5f42d8898fb5fdb304e143c0237 and fixed in 7.3-rc1 with commit b2326338dc683e8c1067c0cbf7a47986c4190902
	Issue introduced in 6.1.178 with commit 115409cbb6a296d73702a62c54c5b1b11cb88b3d

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-89604
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/efivarfs/super.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/8953bdd1b9c0e748d5408d3d0b8e7aeee5c9cd41
	https://git.kernel.org/stable/c/92895a14329cc9533e2a74a265214f690ba3851a
	https://git.kernel.org/stable/c/0dbc2e94b81df5a1264068b6ed3605c654b8afcb
	https://git.kernel.org/stable/c/b2326338dc683e8c1067c0cbf7a47986c4190902