CVE-2026-89499: ring-buffer: Stop remote reader update when page swap fails

CVE-2026-89499: ring-buffer: Stop remote reader update when page swap fails

[Greg Kroah-Hartman]

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

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

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

ring-buffer: Stop remote reader update when page swap fails

The remote swap_reader_page callback can return -EBUSY when the writer
moves the head before the remote catches it, particularly during an event
storm on a small buffer. __rb_get_reader_page_from_remote() currently
warns about that failure but continues with the unchanged reader ID and
rearranges the local page list as though the swap succeeded.

Handle the callback failure as a recoverable error. Report it with
pr_warn_ratelimited() and return NULL. Callers already handle a NULL reader
page as a failed attempt. This avoids splicing the same page as both the
previous and new reader without flooding the log under contention.

The Linux kernel CVE team has assigned CVE-2026-89499 to this issue.


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

	Issue introduced in 7.1 with commit 2e67fabd8b77c4f482df9b211bca1b495c6c2c24 and fixed in 7.2.4 with commit a14a97048e48471e283d76879b83d2ae323e0722
	Issue introduced in 7.1 with commit 2e67fabd8b77c4f482df9b211bca1b495c6c2c24 and fixed in 7.3-rc1 with commit 5eab74874d11160725c42ab676ba97a797a362eb

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-2026-89499
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/a14a97048e48471e283d76879b83d2ae323e0722
	https://git.kernel.org/stable/c/5eab74874d11160725c42ab676ba97a797a362eb