commit a69e617e53 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 23f333a2bf
("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-jZrEA@mail.gmail.com/
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/d1c87ebe9fc502bffcd1576e238d685ad08321e4.1655987888.git.lukas@wunner.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
135199a2ed