CVE-2025-37945

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_suspend() did not call phy_stop_machine() because for

phylink, the phydev->adjust_link function pointer is NULL. This seems a

technicality introduced by commit fddd91016d16 ("phylib: fix PAL state

machine restart on resume"). That commit was written before phylink

existed, and was intended to avoid crashing with consumer drivers which

don't use the PHY state machine - phylink always does, when using a PHY.

But phylink itself has historically not been developed with

suspend/resume in mind, and apparently not tested too much in that

scenario, allowing this bug to exist unnoticed for so long. Plus, prior

to the WARN_ON(), it would have likely been invisible.

This issue is not in fact restricted to type 2 DSA drivers (according to

the above ad-hoc classification), but can be extrapolated to any MAC

driver with phylink and MDIO-bus-managed PHY PM ops. DSA is just where

the issue was reported. Assuming mac_managed_pm is set correctly, a

quick search indicates the following other drivers might be affected:

$ grep -Zlr PHYLINK_NETDEV drivers/ | xargs -0 grep -L mac_managed_pm

drivers/net/ethernet/atheros/ag71xx.c

drivers/net/ethernet/microchip/sparx5/sparx5_main.c

drivers/net/ethernet/microchip/lan966x/lan966x_main.c

drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c

drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c

drivers/net/ethernet/freescale/dpaa/dpaa_eth.c

drivers/net/ethernet/freescale/ucc_geth.c

drivers/net/ethernet/freescale/enetc/enetc_pf_common.c

drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c

drivers/net/ethernet/marvell/mvneta.c

drivers/net/ethernet/marvell/prestera/prestera_main.c

drivers/net/ethernet/mediatek/mtk_eth_soc.c

drivers/net/ethernet/altera/altera_tse_main.c

drivers/net/ethernet/wangxun/txgbe/txgbe_phy.c

drivers/net/ethernet/meta/fbnic/fbnic_phylink.c

drivers/net/ethernet/tehuti/tn40_phy.c

drivers/net/ethernet/mscc/ocelot_net.c

Make the existing conditions dependent on the PHY device having a

phydev->phy_link_change() implementation equal to the default

phy_link_change() provided by phylib. Otherwise, we implicitly know that

the phydev has the phylink-provided phylink_phy_change() callback, and

when phylink is used, the PHY state machine always needs to be stopped/

started on the suspend/resume path. The code is structured as such that

if phydev->phy_link_change() is absent, it is a matter of time until the

kernel will crash - no need to further complicate the test.

Thus, for the situation where the PM is not managed b

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