CVE-2026-64300: perf/aux: Fix page UAF in map_range()

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

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

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

perf/aux: Fix page UAF in map_range()

map_range() reads rb->aux_pages[], rb->aux_nr_pages and rb->aux_pgoff via
perf_mmap_to_page() while holding only event->mmap_mutex. Those fields are
serialized by rb->aux_mutex, and mmap_mutex is per event.

Thus, two events sharing one rb via PERF_EVENT_IOC_SET_OUTPUT can race
rb_alloc_aux() with map_range(), leading to a page-UAF scenario as follows:

  CPU 0                           CPU 1
  =====                           =====
  rb_alloc_aux()                  map_range()
  [1]: allocate rb->aux_pages[0]
  [2]: rb->aux_nr_pages++
                                  [3]: perf_mmap_to_page()
                                         returns rb->aux_pages[0]
                                  [4]: map it as VM_PFNMAP
  [5]: rb->aux_pgoff = 1

  munmap the page
  [6]: free rb->aux_pages[0]

Pages mapped as VM_PFNMAP have no refcount protection, so CPU 1 holds a
mapping to a freed physical frame.

Fix this by taking rb->aux_mutex across the page walk in map_range().

The Linux kernel CVE team has assigned CVE-2026-64300 to this issue.


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

	Issue introduced in 6.14 with commit b709eb872e19a19607bbb6d2975bc264d59735cf and fixed in 6.18.39 with commit c8b7e113f7b61eef2f017e6329c27c2331058c5a
	Issue introduced in 6.14 with commit b709eb872e19a19607bbb6d2975bc264d59735cf and fixed in 7.1.4 with commit 0cff05bd2186020f8706233e261016d149cc24db
	Issue introduced in 6.14 with commit b709eb872e19a19607bbb6d2975bc264d59735cf and fixed in 7.2-rc3 with commit 5948aaf64f81f217a25dcc2bf6c0779bca19566c

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-2026-64300
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/events/core.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/c8b7e113f7b61eef2f017e6329c27c2331058c5a
	https://git.kernel.org/stable/c/0cff05bd2186020f8706233e261016d149cc24db
	https://git.kernel.org/stable/c/5948aaf64f81f217a25dcc2bf6c0779bca19566c