linux-cve-announce - CVE-2025-40042: tracing: Fix race condition in kprobe initialization causing NULL pointer dereference

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Message-ID: <2025102812-CVE-2025-40042-80e6@gregkh>
Date: Tue, 28 Oct 2025 12:48:19 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40042: tracing: Fix race condition in kprobe initialization causing NULL pointer dereference

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

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

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

tracing: Fix race condition in kprobe initialization causing NULL pointer dereference

There is a critical race condition in kprobe initialization that can lead to
NULL pointer dereference and kernel crash.

[1135630.084782] Unable to handle kernel paging request at virtual address 0000710a04630000
...
[1135630.260314] pstate: 404003c9 (nZcv DAIF +PAN -UAO)
[1135630.269239] pc : kprobe_perf_func+0x30/0x260
[1135630.277643] lr : kprobe_dispatcher+0x44/0x60
[1135630.286041] sp : ffffaeff4977fa40
[1135630.293441] x29: ffffaeff4977fa40 x28: ffffaf015340e400
[1135630.302837] x27: 0000000000000000 x26: 0000000000000000
[1135630.312257] x25: ffffaf029ed108a8 x24: ffffaf015340e528
[1135630.321705] x23: ffffaeff4977fc50 x22: ffffaeff4977fc50
[1135630.331154] x21: 0000000000000000 x20: ffffaeff4977fc50
[1135630.340586] x19: ffffaf015340e400 x18: 0000000000000000
[1135630.349985] x17: 0000000000000000 x16: 0000000000000000
[1135630.359285] x15: 0000000000000000 x14: 0000000000000000
[1135630.368445] x13: 0000000000000000 x12: 0000000000000000
[1135630.377473] x11: 0000000000000000 x10: 0000000000000000
[1135630.386411] x9 : 0000000000000000 x8 : 0000000000000000
[1135630.395252] x7 : 0000000000000000 x6 : 0000000000000000
[1135630.403963] x5 : 0000000000000000 x4 : 0000000000000000
[1135630.412545] x3 : 0000710a04630000 x2 : 0000000000000006
[1135630.421021] x1 : ffffaeff4977fc50 x0 : 0000710a04630000
[1135630.429410] Call trace:
[1135630.434828]  kprobe_perf_func+0x30/0x260
[1135630.441661]  kprobe_dispatcher+0x44/0x60
[1135630.448396]  aggr_pre_handler+0x70/0xc8
[1135630.454959]  kprobe_breakpoint_handler+0x140/0x1e0
[1135630.462435]  brk_handler+0xbc/0xd8
[1135630.468437]  do_debug_exception+0x84/0x138
[1135630.475074]  el1_dbg+0x18/0x8c
[1135630.480582]  security_file_permission+0x0/0xd0
[1135630.487426]  vfs_write+0x70/0x1c0
[1135630.493059]  ksys_write+0x5c/0xc8
[1135630.498638]  __arm64_sys_write+0x24/0x30
[1135630.504821]  el0_svc_common+0x78/0x130
[1135630.510838]  el0_svc_handler+0x38/0x78
[1135630.516834]  el0_svc+0x8/0x1b0

kernel/trace/trace_kprobe.c: 1308
0xffff3df8995039ec <kprobe_perf_func+0x2c>:     ldr     x21, [x24,#120]
include/linux/compiler.h: 294
0xffff3df8995039f0 <kprobe_perf_func+0x30>:     ldr     x1, [x21,x0]

kernel/trace/trace_kprobe.c
1308: head = this_cpu_ptr(call->perf_events);
1309: if (hlist_empty(head))
1310: 	return 0;

crash> struct trace_event_call -o
struct trace_event_call {
  ...
  [120] struct hlist_head *perf_events;  //(call->perf_event)
  ...
}

crash> struct trace_event_call ffffaf015340e528
struct trace_event_call {
  ...
  perf_events = 0xffff0ad5fa89f088, //this value is correct, but x21 = 0
  ...
}

Race Condition Analysis:

The race occurs between kprobe activation and perf_events initialization:

  CPU0                                    CPU1
  ====                                    ====
  perf_kprobe_init
    perf_trace_event_init
      tp_event->perf_events = list;(1)
      tp_event->class->reg (2)← KPROBE ACTIVE
                                          Debug exception triggers
                                          ...
                                          kprobe_dispatcher
                                            kprobe_perf_func (tk->tp.flags & TP_FLAG_PROFILE)
                                              head = this_cpu_ptr(call->perf_events)(3)
                                              (perf_events is still NULL)

Problem:
1. CPU0 executes (1) assigning tp_event->perf_events = list
2. CPU0 executes (2) enabling kprobe functionality via class->reg()
3. CPU1 triggers and reaches kprobe_dispatcher
4. CPU1 checks TP_FLAG_PROFILE - condition passes (step 2 completed)
5. CPU1 calls kprobe_perf_func() and crashes at (3) because
   call->perf_events is still NULL

CPU1 sees that kprobe functionality is enabled but does not see that
perf_events has been assigned.

Add pairing read and write memory barriers to guarantee that if CPU1
sees that kprobe functionality is enabled, it must also see that
perf_events has been assigned.

The Linux kernel CVE team has assigned CVE-2025-40042 to this issue.


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

	Issue introduced in 2.6.33 with commit 50d780560785b068c358675c5f0bf6c83b5c373e and fixed in 5.15.195 with commit 95dd33361061f808d1f68616d69ada639e737cfa
	Issue introduced in 2.6.33 with commit 50d780560785b068c358675c5f0bf6c83b5c373e and fixed in 6.1.157 with commit a6e89ada1ff6b70df73f579071ffa6ade8ae7f98
	Issue introduced in 2.6.33 with commit 50d780560785b068c358675c5f0bf6c83b5c373e and fixed in 6.6.113 with commit 1a301228c0a8aedc3154fb1a274456f487416b96
	Issue introduced in 2.6.33 with commit 50d780560785b068c358675c5f0bf6c83b5c373e and fixed in 6.12.54 with commit 0fa388ab2c290ef1115ff88ae88e881d0fb2db02
	Issue introduced in 2.6.33 with commit 50d780560785b068c358675c5f0bf6c83b5c373e and fixed in 6.17.3 with commit 5ebea6561649d30ec7a18fea23d7f76738dae916
	Issue introduced in 2.6.33 with commit 50d780560785b068c358675c5f0bf6c83b5c373e and fixed in 6.18-rc1 with commit 9cf9aa7b0acfde7545c1a1d912576e9bab28dc6f

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-2025-40042
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_fprobe.c
	kernel/trace/trace_kprobe.c
	kernel/trace/trace_probe.h
	kernel/trace/trace_uprobe.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/95dd33361061f808d1f68616d69ada639e737cfa
	https://git.kernel.org/stable/c/a6e89ada1ff6b70df73f579071ffa6ade8ae7f98
	https://git.kernel.org/stable/c/1a301228c0a8aedc3154fb1a274456f487416b96
	https://git.kernel.org/stable/c/0fa388ab2c290ef1115ff88ae88e881d0fb2db02
	https://git.kernel.org/stable/c/5ebea6561649d30ec7a18fea23d7f76738dae916
	https://git.kernel.org/stable/c/9cf9aa7b0acfde7545c1a1d912576e9bab28dc6f