CVE-2025-39745 - rcutorture: Fix rcutorture_one_extend_check() splat in RT kernels

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MEDIUM

rcutorture: Fix rcutorture_one_extend_check() splat in RT kernels

Published Sep 11, 2025

5.5

MEDIUM

CVSS 3.1

EPSS 0.16%

Description

For built with CONFIG_PREEMPT_RT=y kernels, running rcutorture tests resulted in the following splat:

[ 68.797425] rcutorture_one_extend_check during change: Current 0x1 To add 0x1 To remove 0x0 preempt_count() 0x0 [ 68.797533] WARNING: CPU: 2 PID: 512 at kernel/rcu/rcutorture.c:1993 rcutorture_one_extend_check+0x419/0x560 [rcutorture] [ 68.797601] Call Trace: [ 68.797602] <TASK> [ 68.797619] ? lockdep_softirqs_off+0xa5/0x160 [ 68.797631] rcutorture_one_extend+0x18e/0xcc0 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c] [ 68.797646] ? local_clock+0x19/0x40 [ 68.797659] rcu_torture_one_read+0xf0/0x280 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c] [ 68.797678] ? __pfx_rcu_torture_one_read+0x10/0x10 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c] [ 68.797804] ? __pfx_rcu_torture_timer+0x10/0x10 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c] [ 68.797815] rcu-torture: rcu_torture_reader task started [ 68.797824] rcu-torture: Creating rcu_torture_reader task [ 68.797824] rcu_torture_reader+0x238/0x580 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c] [ 68.797836] ? kvm_sched_clock_read+0x15/0x30

Disable BH does not change the SOFTIRQ corresponding bits in preempt_count() for RT kernels, this commit therefore use softirq_count() to check the if BH is disabled.

Affected products

Vendor Linux Product Linux Default
unaffected
- Version
  
  Status
  affected
  Constraints
- Version
  
  Status
  affected
  Constraints
- Version
  
  Status
  affected
  Constraints
Vendor Linux Product Linux Default
affected
- Version
  6.14
  Status
  affected
  Constraints
  -
- Version
  0
  Status
  unaffected
  Constraints
  <6.14
- Version
  6.15.11
  Status
  unaffected
  Constraints
  <=6.15.*
- Version
  6.16.2
  Status
  unaffected
  Constraints
  <=6.16.*
- Version
  6.17
  Status
  unaffected
  Constraints
  <=*

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor

Product

Default status

Versions

Linux

unaffected

Version	Status	Constraints
	affected
	affected
	affected

Linux

affected

Version	Status	Constraints
6.14	affected	-
0	unaffected	<6.14
6.15.11	unaffected	<=6.15.*
6.16.2	unaffected	<=6.16.*
6.17	unaffected	<=*

Red Hat Enterprise Linux 10

kernel

Fix deferred
Red Hat Enterprise Linux 6

kernel

Not affected
Red Hat Enterprise Linux 7

kernel

Not affected
Red Hat Enterprise Linux 7

kernel-rt

Not affected
Red Hat Enterprise Linux 8

kernel

Fix deferred
Red Hat Enterprise Linux 8

kernel-rt

Fix deferred
Red Hat Enterprise Linux 9

kernel

Fix deferred
Red Hat Enterprise Linux 9

kernel-rt

Fix deferred

Product	Package	State	Advisory
Red Hat Enterprise Linux 10	kernel	Fix deferred	n/a
Red Hat Enterprise Linux 6	kernel	Not affected	n/a
Red Hat Enterprise Linux 7	kernel	Not affected	n/a
Red Hat Enterprise Linux 7	kernel-rt	Not affected	n/a
Red Hat Enterprise Linux 8	kernel	Fix deferred	n/a
Red Hat Enterprise Linux 8	kernel-rt	Fix deferred	n/a
Red Hat Enterprise Linux 9	kernel	Fix deferred	n/a
Red Hat Enterprise Linux 9	kernel-rt	Fix deferred	n/a

Remediation

Red Hat mitigation

To mitigate this issue, prevent the `rcutorture` kernel module from loading. This can be achieved by blacklisting the module. Create a file `/etc/modprobe.d/blacklist-rcutorture.conf` with the following content: `blacklist rcutorture` After creating the file, regenerate the initramfs and reboot the system for the changes to take effect: `dracut -f -v` `reboot` This mitigation may impact kernel development or testing environments that rely on the `rcutorture` module. A system reboot is required for the changes to take effect.

Weaknesses (1)

CWE-367

References (9)

Link	Providers	Tags
https://access.redhat.com/security/cve/CVE-2025-39745		Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2394635		Issue Tracking
https://euvd.enisa.europa.eu/vulnerability/EUVD-2025-28966		Advisory
https://git.kernel.org/stable/c/69c5ae0f441c2d72e8f48dc1e08464c172360c4c		Patch
https://git.kernel.org/stable/c/8d71351d88e478d3c4e945e3218e97ec677fd807		Patch
https://git.kernel.org/stable/c/a85550267247cdf5e7499be00ea8e388ab014e50		Patch
https://lore.kernel.org/linux-cve-announce/2025091140-CVE-2025-39745-ac0b@gregkh/T
https://nvd.nist.gov/vuln/detail/CVE-2025-39745
https://www.cve.org/CVERecord?id=CVE-2025-39745