[PATCH v3 1/2] Revert "net: mdiobus: Fix memory leak in __mdiobus_register"

[PATCH v3 1/2] Revert "net: mdiobus: Fix memory leak in __mdiobus_register"

[Pavel Skripkin]

This reverts commit ab609f25d19858513919369ff3d9a63c02cd9e2e.

This patch is correct in the sense that we _should_ call device_put() in
case of device_register() failure, but the problem in this code is more
vast.

We need to set bus->state to UNMDIOBUS_REGISTERED before calling
device_register() to correctly release the device in mdiobus_free().
This patch prevents us from doing it, since in case of device_register()
failure put_device() will be called 2 times and it will cause UAF or
something else.

Also, Reported-by: tag in revered commit was wrong, since syzbot
reported different leak in same function.

Link: https://lore.kernel.org/netdev/20210928092657.GI2048@kadam/
Acked-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---

Changes in v3:
	CC Yanfei -> Acked-by Yanfei

Changes in v2:
	Added this revert

---
 drivers/net/phy/mdio_bus.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 6f4b4e5df639..53f034fc2ef7 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -537,7 +537,6 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
 	err = device_register(&bus->dev);
 	if (err) {
 		pr_err("mii_bus %s failed to register\n", bus->id);
-		put_device(&bus->dev);
 		return -EINVAL;
 	}
 
-- 
2.33.0

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

[Pavel Skripkin]

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@shell.armlinux.org.uk/
Fixes: 46abc02175b3 ("phylib: give mdio buses a device tree presence")
Reported-and-tested-by: syzbot+398e7dc692ddbbb4cfec@syzkaller.appspotmail.com
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---

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
+	 * 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);
-- 
2.33.0

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

[Wong Vee Khee]

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@shell.armlinux.org.uk/
> Fixes: 46abc02175b3 ("phylib: give mdio buses a device tree presence")
> Reported-and-tested-by: syzbot+398e7dc692ddbbb4cfec@syzkaller.appspotmail.com
> Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
> ---
> 
> 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);