Message-ID: <2025120431-CVE-2025-40251-7db7@gregkh>
Date: Thu,  4 Dec 2025 16:57:32 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40251: devlink: rate: Unset parent pointer in devl_rate_nodes_destroy

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

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

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

devlink: rate: Unset parent pointer in devl_rate_nodes_destroy

The function devl_rate_nodes_destroy is documented to "Unset parent for
all rate objects". However, it was only calling the driver-specific
`rate_leaf_parent_set` or `rate_node_parent_set` ops and decrementing
the parent's refcount, without actually setting the
`devlink_rate->parent` pointer to NULL.

This leaves a dangling pointer in the `devlink_rate` struct, which cause
refcount error in netdevsim[1] and mlx5[2]. In addition, this is
inconsistent with the behavior of `devlink_nl_rate_parent_node_set`,
where the parent pointer is correctly cleared.

This patch fixes the issue by explicitly setting `devlink_rate->parent`
to NULL after notifying the driver, thus fulfilling the function's
documented behavior for all rate objects.

[1]
repro steps:
echo 1 > /sys/bus/netdevsim/new_device
devlink dev eswitch set netdevsim/netdevsim1 mode switchdev
echo 1 > /sys/bus/netdevsim/devices/netdevsim1/sriov_numvfs
devlink port function rate add netdevsim/netdevsim1/test_node
devlink port function rate set netdevsim/netdevsim1/128 parent test_node
echo 1 > /sys/bus/netdevsim/del_device

dmesg:
refcount_t: decrement hit 0; leaking memory.
WARNING: CPU: 8 PID: 1530 at lib/refcount.c:31 refcount_warn_saturate+0x42/0xe0
CPU: 8 UID: 0 PID: 1530 Comm: bash Not tainted 6.18.0-rc4+ #1 NONE
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
RIP: 0010:refcount_warn_saturate+0x42/0xe0
Call Trace:
 <TASK>
 devl_rate_leaf_destroy+0x8d/0x90
 __nsim_dev_port_del+0x6c/0x70 [netdevsim]
 nsim_dev_reload_destroy+0x11c/0x140 [netdevsim]
 nsim_drv_remove+0x2b/0xb0 [netdevsim]
 device_release_driver_internal+0x194/0x1f0
 bus_remove_device+0xc6/0x130
 device_del+0x159/0x3c0
 device_unregister+0x1a/0x60
 del_device_store+0x111/0x170 [netdevsim]
 kernfs_fop_write_iter+0x12e/0x1e0
 vfs_write+0x215/0x3d0
 ksys_write+0x5f/0xd0
 do_syscall_64+0x55/0x10f0
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

[2]
devlink dev eswitch set pci/0000:08:00.0 mode switchdev
devlink port add pci/0000:08:00.0 flavour pcisf pfnum 0 sfnum 1000
devlink port function rate add pci/0000:08:00.0/group1
devlink port function rate set pci/0000:08:00.0/32768 parent group1
modprobe -r mlx5_ib mlx5_fwctl mlx5_core

dmesg:
refcount_t: decrement hit 0; leaking memory.
WARNING: CPU: 7 PID: 16151 at lib/refcount.c:31 refcount_warn_saturate+0x42/0xe0
CPU: 7 UID: 0 PID: 16151 Comm: bash Not tainted 6.17.0-rc7_for_upstream_min_debug_2025_10_02_12_44 #1 NONE
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
RIP: 0010:refcount_warn_saturate+0x42/0xe0
Call Trace:
 <TASK>
 devl_rate_leaf_destroy+0x8d/0x90
 mlx5_esw_offloads_devlink_port_unregister+0x33/0x60 [mlx5_core]
 mlx5_esw_offloads_unload_rep+0x3f/0x50 [mlx5_core]
 mlx5_eswitch_unload_sf_vport+0x40/0x90 [mlx5_core]
 mlx5_sf_esw_event+0xc4/0x120 [mlx5_core]
 notifier_call_chain+0x33/0xa0
 blocking_notifier_call_chain+0x3b/0x50
 mlx5_eswitch_disable_locked+0x50/0x110 [mlx5_core]
 mlx5_eswitch_disable+0x63/0x90 [mlx5_core]
 mlx5_unload+0x1d/0x170 [mlx5_core]
 mlx5_uninit_one+0xa2/0x130 [mlx5_core]
 remove_one+0x78/0xd0 [mlx5_core]
 pci_device_remove+0x39/0xa0
 device_release_driver_internal+0x194/0x1f0
 unbind_store+0x99/0xa0
 kernfs_fop_write_iter+0x12e/0x1e0
 vfs_write+0x215/0x3d0
 ksys_write+0x5f/0xd0
 do_syscall_64+0x53/0x1f0
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

The Linux kernel CVE team has assigned CVE-2025-40251 to this issue.


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

	Issue introduced in 5.14 with commit d7555984507822458b32a6405881038241d140be and fixed in 6.6.118 with commit 715d9cda646a8a38ea8b2bb5afb679a7464055e2
	Issue introduced in 5.14 with commit d7555984507822458b32a6405881038241d140be and fixed in 6.12.60 with commit c70df6c17d389cc743f0eb30160e2d6bc6910db8
	Issue introduced in 5.14 with commit d7555984507822458b32a6405881038241d140be and fixed in 6.17.10 with commit 542f45486f1ce2d2dde75bd85aca0389ef7046c3
	Issue introduced in 5.14 with commit d7555984507822458b32a6405881038241d140be and fixed in 6.18 with commit f94c1a114ac209977bdf5ca841b98424295ab1f0

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-2025-40251
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:
	net/devlink/rate.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/715d9cda646a8a38ea8b2bb5afb679a7464055e2
	https://git.kernel.org/stable/c/c70df6c17d389cc743f0eb30160e2d6bc6910db8
	https://git.kernel.org/stable/c/542f45486f1ce2d2dde75bd85aca0389ef7046c3
	https://git.kernel.org/stable/c/f94c1a114ac209977bdf5ca841b98424295ab1f0

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