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net: macb: fix NULL pointer dereference on unbind with fixed-link

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When the device tree describes a fixed-link and has no "mdio" child
node, macb_mii_init() returns early without allocating the MDIO bus,
leaving bp->mii_bus as NULL.

Two cleanup paths then dereference this NULL bus:

1. On driver unbind, macb_remove() unconditionally calls
   mdiobus_unregister(bp->mii_bus), which oopses:

  Unable to handle kernel NULL pointer dereference at virtual address 00000000000004a8
  pc : mdiobus_unregister+0x14/0xa4
  lr : macb_remove+0x38/0xa4
  Call trace:
   mdiobus_unregister+0x14/0xa4 (P)
   macb_remove+0x38/0xa4
   platform_remove+0x20/0x30
   device_release_driver_internal+0x1c8/0x224
   unbind_store+0xb4/0xbc

2. On the probe error path in macb_probe(), reached when
   macb_mii_init() has succeeded but a subsequent step fails, the
   err_out_unregister_mdio label runs the same unconditional cleanup.

mdiobus_unregister() and mdiobus_free() do not guard against a NULL
bus, so guard the calls in both macb_remove() and the probe error
path.

Fixes: d0c3601f2c ("net: macb: Avoid 20s boot delay by skipping MDIO bus registration for fixed-link PHY")
Signed-off-by: Vineeth Karumanchi <vineeth.karumanchi@amd.com>
Reviewed-by: Xuanqiang Luo <luoxuanqiang@kylinos.cn>
Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>
Link: https://patch.msgid.link/20260902102836.2019355-1-vineeth.karumanchi@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Vineeth Karumanchi 2026-09-02 15:58:36 +05:30 committed by Jakub Kicinski
parent e7c93ad4bd
commit 38b6be1010
1 changed files with 8 additions and 4 deletions
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12
drivers/net/ethernet/cadence/macb_main.c
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@ -5976,8 +5976,10 @@ static int macb_probe(struct platform_device *pdev)
macb_free_tieoff(bp);
err_out_unregister_mdio:
mdiobus_unregister(bp->mii_bus);
mdiobus_free(bp->mii_bus);
if (bp->mii_bus) {
mdiobus_unregister(bp->mii_bus);
mdiobus_free(bp->mii_bus);
}
err_out_phy_exit:
phy_exit(bp->phy);
@ -6006,8 +6008,10 @@ static void macb_remove(struct platform_device *pdev)
unregister_netdev(netdev);
macb_free_tieoff(bp);
phy_exit(bp->phy);
mdiobus_unregister(bp->mii_bus);
mdiobus_free(bp->mii_bus);
if (bp->mii_bus) {
mdiobus_unregister(bp->mii_bus);
mdiobus_free(bp->mii_bus);
}
device_set_wakeup_enable(&bp->pdev->dev, 0);
cancel_delayed_work_sync(&bp->tx_lpi_work);