Re: [syzbot] memory leak in __mdiobus_register

[Pavel Skripkin]

On 9/26/21 04:28, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    d9fb678414c0 Merge tag 'afs-fixes-20210913' of git://git.k..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=131c754b300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f0de362a1f17687e
> dashboard link: https://syzkaller.appspot.com/bug?extid=398e7dc692ddbbb4cfec
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=145650d1300000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=105ccde7300000

Looks like MDIOBUS_ALLOCATED indicated 2 states:

	1. Bus is only allocated
	2. Bus allocated and __mdiobus_register() fails, but
	   device_register() was called

These 2 cases should be handled separately, i.e. we need to call 
put_device() if device_register() was called.

To handle this situation we can add new state MDIOBUS_DEV_REGISTERED and 
handle it properly


Just for thoughts and syzbot testing

#syz test
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


With regards,
Pavel Skripkin





diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 53f034fc2ef7..ed764638b449 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -540,6 +540,8 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
 		return -EINVAL;
 	}
 
+	bus->state = MDIOBUS_DEV_REGISTERED;
+
 	mutex_init(&bus->mdio_lock);
 	mutex_init(&bus->shared_lock);
 
@@ -647,7 +649,7 @@ void mdiobus_free(struct mii_bus *bus)
 		return;
 	}
 
-	BUG_ON(bus->state != MDIOBUS_UNREGISTERED);
+	BUG_ON(bus->state != MDIOBUS_UNREGISTERED && bus->state != MDIOBUS_DEV_REGISTERED);
 	bus->state = MDIOBUS_RELEASED;
 
 	put_device(&bus->dev);
diff --git a/include/linux/phy.h b/include/linux/phy.h
index 736e1d1a47c4..41d2ccdacd5e 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -343,6 +343,7 @@ struct mii_bus {
 		MDIOBUS_REGISTERED,
 		MDIOBUS_UNREGISTERED,
 		MDIOBUS_RELEASED,
+		MDIOBUS_DEV_REGISTERED,
 	} state;
 
 	/** @dev: Kernel device representation */