usbnet: Run unregister_netdev() before unbind() again

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: usbnet: Run unregister_netdev() before unbind() again Commit 2c9d6c2b871d ("usbnet: run unbind() before unregister_netdev()") sought to fix a use-after-free on disconnect of USB Ethernet adapters. It turns out that a different fix is necessary to address the issue: https://lore.kernel.org/netdev/18b3541e5372bc9b9fc733d422f4e698c089077c.1650177997.git.lukas@wunner.de/ So the commit was not necessary. The commit made binding and unbinding of USB Ethernet asymmetrical: Before, usbnet_probe() first invoked the ->bind() callback and then register_netdev(). usbnet_disconnect() mirrored that by first invoking unregister_netdev() and then ->unbind(). Since the commit, the order in usbnet_disconnect() is reversed and no longer mirrors usbnet_probe(). One consequence is that a PHY disconnected (and stopped) in ->unbind() is afterwards stopped once more by unregister_netdev() as it closes the netdev before unregistering. That necessitates a contortion in ->stop() because the PHY may only be stopped if it hasn't already been disconnected. Reverting the commit allows making the call to phy_stop() unconditional in ->stop().

References

• https://git.kernel.org/stable/c/6d5deb242874d924beccf7eb3cef04c1c3b0da79
• https://git.kernel.org/stable/c/fbda837107f9bd4ec658d2aa88c6856dba606f06
• https://git.kernel.org/stable/c/969a1b3ea3cb7d58a16fe12fd1b04bfc0ea40509
• https://git.kernel.org/stable/c/d1408f6b4dd78fb1b9e26bcf64477984e5f85409