[PATCH v4 1/2] Revert "net: mdiobus: Fix memory leak in __mdiobus_register"

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 <redacted>
Signed-off-by: Pavel Skripkin <redacted>
---

Chnages in v4:
	No changes

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

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 <redacted>
Signed-off-by: Pavel Skripkin <redacted>
---

Changes in v4:
	Fixed typo in comment, thanks to Wong Vee Khee

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..fca8e335d750 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 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);

-- 
2.33.0

Hello:

This series was applied to netdev/net.git (refs/heads/master):

On Thu, 30 Sep 2021 20:49:42 +0300 you wrote:

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.

[...]

Here is the summary with links:
  - [v4,1/2] Revert "net: mdiobus: Fix memory leak in __mdiobus_register"
    https://git.kernel.org/netdev/net/c/10eff1f5788b
  - [v4,2/2] phy: mdio: fix memory leak
    https://git.kernel.org/netdev/net/c/ca6e11c337da

You are awesome, thank you!
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