CVE-2026-74636: tracing: Fix race between update_event_fields and, event_define_fields

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

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

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

tracing: Fix race between update_event_fields and, event_define_fields

The following sequence may leads race between event_define_fields()
and update_event_fields():

 CPU0 (loads module A)                      CPU1 (loads module B)
 ===============================            ===============================
 load_module(A)                             load_module(B)
   notifier_call_chain                        notifier_call_chain
     trace_module_notify                        trace_module_notify
       mutex_lock(&event_mutex)                   trace_event_update_all()
         trace_module_add_events(A)                 down_write(&trace_event_sem)
            __register_event(call_A)
              __add_event_to_tracers(call_A)
                event_define_fields(call_A)
                  for each f:                         list_for_each_entry(field,
                    list_add(&f->link,                                    &class->fields, link)
                             &class->fields)            field = class->fields->next;

Where access to the class->fields is not protected by the event_mutex in
trace_event_update_all().

This produces the following panic:
   Unable to handle kernel access ... at virtual address 0000000000000018
   pc : update_event_fields+0xf8/0x368
   Call trace:
    update_event_fields+0xf8/0x368
    trace_event_update_all+0x7c/0x2b4
    trace_module_notify+0x4c/0x1dc
    notifier_call_chain+0x84/0x168
    blocking_notifier_call_chain_robust+0x64/0xd4
    load_module+0x10c8/0x123c
    __arm64_sys_finit_module+0x230/0x31c

Fix by taking event_mutex in trace_event_update_all() before
trace_event_sem.

The Linux kernel CVE team has assigned CVE-2026-74636 to this issue.


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

	Issue introduced in 5.15.33 with commit 7c6bd60999f32138e3b73fd97ea11ef47a94de25 and fixed in 5.15.216 with commit 4e39f7b4d9d36508c53e89e6cbc640728df870b5
	Issue introduced in 5.18 with commit b3bc8547d3be60898818885f5bf22d0a62e2eb48 and fixed in 6.1.183 with commit a30d421468300b1e7b2f233136aeb2db8013f555
	Issue introduced in 5.18 with commit b3bc8547d3be60898818885f5bf22d0a62e2eb48 and fixed in 6.6.152 with commit e5f1d301b4bdaa4206db251fdc691f623162b0a8
	Issue introduced in 5.18 with commit b3bc8547d3be60898818885f5bf22d0a62e2eb48 and fixed in 6.12.104 with commit fdeb190b0905a6aaed1e5d6adfb8613214748d7d
	Issue introduced in 5.18 with commit b3bc8547d3be60898818885f5bf22d0a62e2eb48 and fixed in 6.18.45 with commit ed49684e69f846bf50b5050651ccdb87cfd152c0
	Issue introduced in 5.18 with commit b3bc8547d3be60898818885f5bf22d0a62e2eb48 and fixed in 7.1.9 with commit f128740f39ab28d1f4ad5bdd10f3e117eec0c374
	Issue introduced in 5.18 with commit b3bc8547d3be60898818885f5bf22d0a62e2eb48 and fixed in 7.2 with commit c3730b8373bb5059d735509b9e6a00d7eb337d7c
	Issue introduced in 5.16.19 with commit 55defdf935fab9f2989a197aae1042c082d9a343
	Issue introduced in 5.17.2 with commit 0c53a5c80e6e286733381a1d9f255ba4039e2e45

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-2026-74636
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/trace_events.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/4e39f7b4d9d36508c53e89e6cbc640728df870b5
	https://git.kernel.org/stable/c/a30d421468300b1e7b2f233136aeb2db8013f555
	https://git.kernel.org/stable/c/e5f1d301b4bdaa4206db251fdc691f623162b0a8
	https://git.kernel.org/stable/c/fdeb190b0905a6aaed1e5d6adfb8613214748d7d
	https://git.kernel.org/stable/c/ed49684e69f846bf50b5050651ccdb87cfd152c0
	https://git.kernel.org/stable/c/f128740f39ab28d1f4ad5bdd10f3e117eec0c374
	https://git.kernel.org/stable/c/c3730b8373bb5059d735509b9e6a00d7eb337d7c