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 dsaswitchsuspend() and dsaswitchresume() 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, dsaswitchsuspend() calls dsausersuspend() -> phylinkstop(), and dsaswitchresume() calls dsauserresume() -> phylinkstart(). These seem good candidates for setting macmanagedpm = 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, mdiobusphysuspend() and mdiobusphyresume() should run in full), I have noticed that the following warning from mdiobusphy_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 dsauseropen() -> ... -> phylinkstart() -> phystart() having been initiated by the user.

The previous mdiobusphysuspend() was supposed to have called phystopmachine(), but it didn't. So this is why the PHY is in state PHYNOLINK by the time mdiobusphy_resume() runs.

mdiobusphysuspend() did not call phystopmachine() because for phylink, the phydev->adjustlink 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 macmanagedpm is set correctly, a quick search indicates the following other drivers might be affected:

$ grep -Zlr PHYLINKNETDEV drivers/ | xargs -0 grep -L macmanagedpm drivers/net/ethernet/atheros/ag71xx.c drivers/net/ethernet/microchip/sparx5/sparx5main.c drivers/net/ethernet/microchip/lan966x/lan966xmain.c drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c drivers/net/ethernet/freescale/fsenet/fsenet-main.c drivers/net/ethernet/freescale/dpaa/dpaaeth.c drivers/net/ethernet/freescale/uccgeth.c drivers/net/ethernet/freescale/enetc/enetcpfcommon.c drivers/net/ethernet/marvell/mvpp2/mvpp2main.c drivers/net/ethernet/marvell/mvneta.c drivers/net/ethernet/marvell/prestera/presteramain.c drivers/net/ethernet/mediatek/mtkethsoc.c drivers/net/ethernet/altera/alteratsemain.c drivers/net/ethernet/wangxun/txgbe/txgbephy.c drivers/net/ethernet/meta/fbnic/fbnicphylink.c drivers/net/ethernet/tehuti/tn40phy.c drivers/net/ethernet/mscc/ocelot_net.c

Make the existing conditions dependent on the PHY device having a phydev->phylinkchange() implementation equal to the default phylinkchange() provided by phylib. Otherwise, we implicitly know that the phydev has the phylink-provided phylinkphychange() 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->phylinkchange() 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 ---truncated---