CVE-2022-50220 Information

Jun 19, 2025 cve

Description

In the Linux kernel the following vulnerability has been resolved:

usbnet: Fix linkwatch use-after-free on disconnect

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_onoff(). That in turn schedules the work linkwatch_event().

Because usbnet_deferred_kevent() is awaited after unregister_netdev() netif_carrier_onoff() 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.

Reference

https://git.kernel.org/stable/c/135199a2edd459d2b123144efcd7f9bcd95128e4 https://git.kernel.org/stable/c/635fd8953e4309b54ca6a81bed1d4a87668694f4 https://git.kernel.org/stable/c/7f77dcbc030c2faa6d8e8a594985eeb34018409e https://git.kernel.org/stable/c/8b4588b8b00b299be16a35be67b331d8fdba03f3 https://git.kernel.org/stable/c/a69e617e533edddf3fa3123149900f36e0a6dc74 https://git.kernel.org/stable/c/d2d6b530d89b0a912148018027386aa049f0a309 https://git.kernel.org/stable/c/d49bb8cf9bfaa06aa527eb30f1a52a071da2e32f https://git.kernel.org/stable/c/db3b738ae5f726204876f4303c49cfdf4311403f https://git.kernel.org/stable/c/e2a521a7dcc463c5017b4426ca0804e151faeff7

CNNVD-202506-2510 (Published: 2025-06-18)

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