Linux Kernel af_packet Notifier Context Vulnerability

A vulnerability in the Linux kernel's af_packet component has been addressed. The issue arose because a sleeping function was called from an invalid context, disrupting proper mutex locking. This vulnerability could be triggered by invoking `PACKET_ADD_MEMBERSHIP` on a device that is locked by operations, which would then activate the `NETDEV_UNREGISTER` notifier. Such a scenario requires disabling promiscuous mode and all-multi mode, operations that depend on the netdev instance lock. The vulnerability has been resolved by relocating the `packet_dev_mc` call out of the RCU critical section, ensuring that modifications to the multicast list are properly managed under the RTNL protection, rather than the RCU.

Impact

Exploitation of this vulnerability could lead to improper handling of network device notifiers, potentially causing synchronization issues or incorrect network device state management.