CVE-2026-74634: ring-buffer: Prevent subbuf order change when resizing is disabled

From: Greg Kroah-Hartman <[email protected]>

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

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

ring-buffer: Prevent subbuf order change when resizing is disabled

Because ring_buffer_subbuf_order_set() frees buffer pages, we can't
allow it when resizing is disabled. A non-consuming reader is at risk of
use-after-free (rb_advance_iter()).

Return -EBUSY on resize_disabled, matching ring_buffer_resize()
behaviour.

The Linux kernel CVE team has assigned CVE-2026-74634 to this issue.


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

	Issue introduced in 6.8 with commit f9b94daa542a8d2532f0930f01cd9aec2d19621b and fixed in 6.12.104 with commit b45b91db41379ee5fb36c187d6d7c37b725cbe8e
	Issue introduced in 6.8 with commit f9b94daa542a8d2532f0930f01cd9aec2d19621b and fixed in 6.18.45 with commit 62978cf6347972c04130e4e841ba404504d92b32
	Issue introduced in 6.8 with commit f9b94daa542a8d2532f0930f01cd9aec2d19621b and fixed in 7.1.9 with commit 7568e9e717e7540bd05bcc007f5d76fcaff3cdff
	Issue introduced in 6.8 with commit f9b94daa542a8d2532f0930f01cd9aec2d19621b and fixed in 7.2 with commit bf98d7b0d5a99991e47e66cee4eb1d3fa514be97

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-2026-74634
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:
	kernel/trace/ring_buffer.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/b45b91db41379ee5fb36c187d6d7c37b725cbe8e
	https://git.kernel.org/stable/c/62978cf6347972c04130e4e841ba404504d92b32
	https://git.kernel.org/stable/c/7568e9e717e7540bd05bcc007f5d76fcaff3cdff
	https://git.kernel.org/stable/c/bf98d7b0d5a99991e47e66cee4eb1d3fa514be97