CVE-2026-89503: ring-buffer: Fix subbuf resize race with ring_buffer_alloc_read_page()

CVE-2026-89503: ring-buffer: Fix subbuf resize race with ring_buffer_alloc_read_page()

[Greg Kroah-Hartman]

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

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

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

ring-buffer: Fix subbuf resize race with ring_buffer_alloc_read_page()

ring_buffer_alloc_read_page() is racy with ring_buffer_subbuf_order_set,
it can allocate a reader page with an outdated order. This isn't a big
issue, the user can still re-allocate a new reader page and try again.

However, what is more problematic is if the value of subbuf_order
changes in the middle of ring_buffer_alloc_read_page(). In that case,
bpage->order might not match the actual allocated memory.

Use bpage->order for the allocation to prevent this race.

The Linux kernel CVE team has assigned CVE-2026-89503 to this issue.


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

	Issue introduced in 6.8 with commit bce761d757452ba5eb77e11fecc37a04b67494e7 and fixed in 6.18.50 with commit 2dc510957fe8fd098ab3c3147ebdf34d00cd2734
	Issue introduced in 6.8 with commit bce761d757452ba5eb77e11fecc37a04b67494e7 and fixed in 7.2.4 with commit 53106e9262a310ef2c9a9321168c03705940c678
	Issue introduced in 6.8 with commit bce761d757452ba5eb77e11fecc37a04b67494e7 and fixed in 7.3-rc1 with commit e743527c5bfdceda1095bc0a9e596e2aebb6a9c3

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-2026-89503
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/2dc510957fe8fd098ab3c3147ebdf34d00cd2734
	https://git.kernel.org/stable/c/53106e9262a310ef2c9a9321168c03705940c678
	https://git.kernel.org/stable/c/e743527c5bfdceda1095bc0a9e596e2aebb6a9c3