a69e617e53
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-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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.