net: dsa: fix panic when DSA master device unbinds on shutdown

Summary

In the Linux kernel, the following vulnerability has been resolved: net: dsa: fix panic when DSA master device unbinds on shutdown Rafael reports that on a system with LX2160A and Marvell DSA switches, if a reboot occurs while the DSA master (dpaa2-eth) is up, the following panic can be seen: systemd-shutdown[1]: Rebooting. Unable to handle kernel paging request at virtual address 00a0000800000041 [00a0000800000041] address between user and kernel address ranges Internal error: Oops: 96000004 [#1] PREEMPT SMP CPU: 6 PID: 1 Comm: systemd-shutdow Not tainted 5.16.5-00042-g8f5585009b24 #32 pc : dsa_slave_netdevice_event+0x130/0x3e4 lr : raw_notifier_call_chain+0x50/0x6c Call trace: dsa_slave_netdevice_event+0x130/0x3e4 raw_notifier_call_chain+0x50/0x6c call_netdevice_notifiers_info+0x54/0xa0 __dev_close_many+0x50/0x130 dev_close_many+0x84/0x120 unregister_netdevice_many+0x130/0x710 unregister_netdevice_queue+0x8c/0xd0 unregister_netdev+0x20/0x30 dpaa2_eth_remove+0x68/0x190 fsl_mc_driver_remove+0x20/0x5c __device_release_driver+0x21c/0x220 device_release_driver_internal+0xac/0xb0 device_links_unbind_consumers+0xd4/0x100 __device_release_driver+0x94/0x220 device_release_driver+0x28/0x40 bus_remove_device+0x118/0x124 device_del+0x174/0x420 fsl_mc_device_remove+0x24/0x40 __fsl_mc_device_remove+0xc/0x20 device_for_each_child+0x58/0xa0 dprc_remove+0x90/0xb0 fsl_mc_driver_remove+0x20/0x5c __device_release_driver+0x21c/0x220 device_release_driver+0x28/0x40 bus_remove_device+0x118/0x124 device_del+0x174/0x420 fsl_mc_bus_remove+0x80/0x100 fsl_mc_bus_shutdown+0xc/0x1c platform_shutdown+0x20/0x30 device_shutdown+0x154/0x330 __do_sys_reboot+0x1cc/0x250 __arm64_sys_reboot+0x20/0x30 invoke_syscall.constprop.0+0x4c/0xe0 do_el0_svc+0x4c/0x150 el0_svc+0x24/0xb0 el0t_64_sync_handler+0xa8/0xb0 el0t_64_sync+0x178/0x17c It can be seen from the stack trace that the problem is that the deregistration of the master causes a dev_close(), which gets notified as NETDEV_GOING_DOWN to dsa_slave_netdevice_event(). But dsa_switch_shutdown() has already run, and this has unregistered the DSA slave interfaces, and yet, the NETDEV_GOING_DOWN handler attempts to call dev_close_many() on those slave interfaces, leading to the problem. The previous attempt to avoid the NETDEV_GOING_DOWN on the master after dsa_switch_shutdown() was called seems improper. Unregistering the slave interfaces is unnecessary and unhelpful. Instead, after the slaves have stopped being uppers of the DSA master, we can now reset to NULL the master->dsa_ptr pointer, which will make DSA start ignoring all future notifier events on the master.