Re: [PATCH v3 2/2] phy: mdio: fix memory leak

From: Wong Vee Khee
Date: Thu Sep 30 2021 - 02:45:13 EST


On Thu, Sep 30, 2021 at 09:19:54AM +0300, Pavel Skripkin wrote:
> Syzbot reported memory leak in MDIO bus interface, the problem was in
> wrong state logic.
>
> MDIOBUS_ALLOCATED indicates 2 states:
> 1. Bus is only allocated
> 2. Bus allocated and __mdiobus_register() fails, but
> device_register() was called
>
> In case of device_register() has been called we should call put_device()
> to correctly free the memory allocated for this device, but mdiobus_free()
> calls just kfree(dev) in case of MDIOBUS_ALLOCATED state
>
> To avoid this behaviour we need to set bus->state to MDIOBUS_UNREGISTERED
> _before_ calling device_register(), because put_device() should be
> called even in case of device_register() failure.
>
> Link: https://lore.kernel.org/netdev/YVMRWNDZDUOvQjHL@xxxxxxxxxxxxxxxxxxxxx/
> Fixes: 46abc02175b3 ("phylib: give mdio buses a device tree presence")
> Reported-and-tested-by: syzbot+398e7dc692ddbbb4cfec@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reviewed-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> Signed-off-by: Pavel Skripkin <paskripkin@xxxxxxxxx>
> ---
>
> Changes in v3:
> s/==/=/
> Added Dan's Reviewed-by tag
>
> Changes in v2:
> Removed new state, since MDIOBUS_UNREGISTERED can be used. Also, moved
> bus->state initialization _before_ device_register() call, because
> Yanfei's patch is reverted in [v2 1/2]
>
> ---
> drivers/net/phy/mdio_bus.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
> index 53f034fc2ef7..a5f910d4a7be 100644
> --- a/drivers/net/phy/mdio_bus.c
> +++ b/drivers/net/phy/mdio_bus.c
> @@ -534,6 +534,13 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
> bus->dev.groups = NULL;
> dev_set_name(&bus->dev, "%s", bus->id);
>
> + /* We need to set state to MDIOBUS_UNREGISTERED to correctly realese

Typo here. s/realese/release/

> + * the device in mdiobus_free()
> + *
> + * State will be updated later in this function in case of success
> + */
> + bus->state = MDIOBUS_UNREGISTERED;
> +
> err = device_register(&bus->dev);
> if (err) {
> pr_err("mii_bus %s failed to register\n", bus->id);