Description

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

net: phy: allow MDIO bus PM ops to start/stop state machine for phylink-controlled PHY

DSA has 2 kinds of drivers:

1. Those who call dsa_switch_suspend() and dsa_switch_resume() from
their device PM ops: qca8k-8xxx, bcm_sf2, microchip ksz
2. Those who don't: all others. The above methods should be optional.

For type 1, dsa_switch_suspend() calls dsa_user_suspend() -> phylink_stop(),
and dsa_switch_resume() calls dsa_user_resume() -> phylink_start().
These seem good candidates for setting mac_managed_pm = true because
that is essentially its definition [1], but that does not seem to be the
biggest problem for now, and is not what this change focuses on.

Talking strictly about the 2nd category of DSA drivers here (which
do not have MAC managed PM, meaning that for their attached PHYs,
mdio_bus_phy_suspend() and mdio_bus_phy_resume() should run in full),
I have noticed that the following warning from mdio_bus_phy_resume() is
triggered:

WARN_ON(phydev->state != PHY_HALTED && phydev->state != PHY_READY &&
phydev->state != PHY_UP);

because the PHY state machine is running.

It's running as a result of a previous dsa_user_open() -> ... ->
phylink_start() -> phy_start() having been initiated by the user.

The previous mdio_bus_phy_suspend() was supposed to have called
phy_stop_machine(), but it didn't. So this is why the PHY is in state
PHY_NOLINK by the time mdio_bus_phy_resume() runs.

mdio_bus_phy_...

Classification

CVE ID: CVE-2025-37945

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.02% (probability of being exploited)

EPSS Percentile: 4.6% (scored less or equal to compared to others)

EPSS Date: 2025-06-12 (when was this score calculated)

References

https://nvd.nist.gov/vuln/detail/CVE-2025-37945
https://git.kernel.org/stable/c/a6ed6f8ec81b8ca7100dcd9e62bdbc0dff1b2259
https://git.kernel.org/stable/c/54e5d00a8de6c13f6c01a94ed48025e882cd15f7
https://git.kernel.org/stable/c/bd4037d51d3f6667636a1383e78e48a5b7b60755
https://git.kernel.org/stable/c/fc75ea20ffb452652f0d4033f38fe88d7cfdae35

Timeline