CVE-2026-64402: coresight: ultrasoc-smb: Fix OOB write in smb_sync_perf_buffer()

CVE-2026-64402: coresight: ultrasoc-smb: Fix OOB write in smb_sync_perf_buffer()

[Greg Kroah-Hartman]

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

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

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

coresight: ultrasoc-smb: Fix OOB write in smb_sync_perf_buffer()

When the SMB sink is used as a perf AUX sink, smb_update_buffer() calls
smb_sync_perf_buffer() to copy hardware trace data into the perf AUX ring
buffer pages. It derives pg_idx = head >> PAGE_SHIFT from @head, which is
handle->head, and indexes dst_pages[pg_idx]. The pg_idx %= nr_pages
normalization is only applied after the first loop iteration.

This leaves the initial page index underived from the buffer size, which
can result in an out-of-bounds write past dst_pages[] when head exceeds
the AUX buffer size.

Normalize head modulo the AUX buffer size before deriving the page index
and offset, mirroring tmc_etr_sync_perf_buffer().

The Linux kernel CVE team has assigned CVE-2026-64402 to this issue.


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

	Issue introduced in 6.3 with commit 06f5c2926aaa0fba7f99678da6ef77cbbbda1441 and fixed in 6.6.145 with commit 38dbc8db8341ccdf8e1e1a067453d33ad751864b
	Issue introduced in 6.3 with commit 06f5c2926aaa0fba7f99678da6ef77cbbbda1441 and fixed in 6.12.96 with commit 4c5a0a946373da99a80398289b28845b5ae40cd1
	Issue introduced in 6.3 with commit 06f5c2926aaa0fba7f99678da6ef77cbbbda1441 and fixed in 6.18.39 with commit 661a019ac0413ecec9e5d1dfcc12fbca8e78d5fb
	Issue introduced in 6.3 with commit 06f5c2926aaa0fba7f99678da6ef77cbbbda1441 and fixed in 7.1.4 with commit daf6246ab988fc8bdc82ad7c8d0b1c182d11b15f
	Issue introduced in 6.3 with commit 06f5c2926aaa0fba7f99678da6ef77cbbbda1441 and fixed in 7.2-rc1 with commit 98495b5a4d77dd22e106f462b76e1093a55b29a7

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-2026-64402
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:
	drivers/hwtracing/coresight/ultrasoc-smb.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/38dbc8db8341ccdf8e1e1a067453d33ad751864b
	https://git.kernel.org/stable/c/4c5a0a946373da99a80398289b28845b5ae40cd1
	https://git.kernel.org/stable/c/661a019ac0413ecec9e5d1dfcc12fbca8e78d5fb
	https://git.kernel.org/stable/c/daf6246ab988fc8bdc82ad7c8d0b1c182d11b15f
	https://git.kernel.org/stable/c/98495b5a4d77dd22e106f462b76e1093a55b29a7