From: Lukas Wunner lukas@wunner.de
commit a69e617e533edddf3fa3123149900f36e0a6dc74 upstream.
usbnet uses the work usbnet_deferred_kevent() to perform tasks which may sleep. On disconnect, completion of the work was originally awaited in ->ndo_stop(). But in 2003, that was moved to ->disconnect() by historic commit "[PATCH] USB: usbnet, prevent exotic rtnl deadlock":
https://git.kernel.org/tglx/history/c/0f138bbfd83c
The change was made because back then, the kernel's workqueue implementation did not allow waiting for a single work. One had to wait for completion of *all* work by calling flush_scheduled_work(), and that could deadlock when waiting for usbnet_deferred_kevent() with rtnl_mutex held in ->ndo_stop().
The commit solved one problem but created another: It causes a use-after-free in USB Ethernet drivers aqc111.c, asix_devices.c, ax88179_178a.c, ch9200.c and smsc75xx.c:
* If the drivers receive a link change interrupt immediately before disconnect, they raise EVENT_LINK_RESET in their (non-sleepable) ->status() callback and schedule usbnet_deferred_kevent(). * usbnet_deferred_kevent() invokes the driver's ->link_reset() callback, which calls netif_carrier_{on,off}(). * That in turn schedules the work linkwatch_event().
Because usbnet_deferred_kevent() is awaited after unregister_netdev(), netif_carrier_{on,off}() may operate on an unregistered netdev and linkwatch_event() may run after free_netdev(), causing a use-after-free.
In 2010, usbnet was changed to only wait for a single instance of usbnet_deferred_kevent() instead of *all* work by commit 23f333a2bfaf ("drivers/net: don't use flush_scheduled_work()").
Unfortunately the commit neglected to move the wait back to ->ndo_stop(). Rectify that omission at long last.
Reported-by: Jann Horn jannh@google.com Link: https://lore.kernel.org/netdev/CAG48ez0MHBbENX5gCdHAUXZ7h7s20LnepBF-pa5M=7Bi... Reported-by: Oleksij Rempel o.rempel@pengutronix.de Link: https://lore.kernel.org/netdev/20220315113841.GA22337@pengutronix.de/ Signed-off-by: Lukas Wunner lukas@wunner.de Cc: stable@vger.kernel.org Acked-by: Oliver Neukum oneukum@suse.com Link: https://lore.kernel.org/r/d1c87ebe9fc502bffcd1576e238d685ad08321e4.165598788... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/usb/usbnet.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
--- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -847,13 +847,11 @@ int usbnet_stop (struct net_device *net)
mpn = !test_and_clear_bit(EVENT_NO_RUNTIME_PM, &dev->flags);
- /* deferred work (task, timer, softirq) must also stop. - * can't flush_scheduled_work() until we drop rtnl (later), - * else workers could deadlock; so make workers a NOP. - */ + /* deferred work (timer, softirq, task) must also stop */ dev->flags = 0; del_timer_sync (&dev->delay); tasklet_kill (&dev->bh); + cancel_work_sync(&dev->kevent); if (!pm) usb_autopm_put_interface(dev->intf);
@@ -1577,8 +1575,6 @@ void usbnet_disconnect (struct usb_inter net = dev->net; unregister_netdev (net);
- cancel_work_sync(&dev->kevent); - usb_scuttle_anchored_urbs(&dev->deferred);
if (dev->driver_info->unbind)