CVE-2026-63905: usbip: vudc: Fix use after free bug in vudc_remove due to race condition
In the Linux kernel, the following vulnerability has been resolved:
usbip: vudc: Fix use after free bug in vudcremove due to race condition
This patch follows up Zheng Wang's 2023 report of a use-after-free in vudcremove(). The original thread stalled on Shuah Khan's request for runtime testing of the unplug/unbind path. This patch supplies that testing and keeps Zheng's original fix shape.
In vudcprobe(), vinittimer() binds udc->trtimer.timer to vtimer(). usbipsockfdstore() starts the timer via vstarttimer()/vkicktimer(). vudcremove() can then free the containing struct vudc while the timer is still pending or executing.
KASAN confirms the race on an unpatched x8664 QEMU guest with CONFIGKASAN=y, CONFIGUSBIPVUDC=y, CONFIGUSBZERO=y, and a tight loop that repeatedly writes a socket fd to usbipsockfd, closes the socket pair, and unbinds/rebinds usbip-vudc.0:
BUG: KASAN: slab-use-after-free in runtimerbase.part.0+0x8ba/0x8e0 Write of size 8 at addr ffff888001b80740 by task triggerandunb/239 Allocated by task 239: vudcprobe+0x4d/0xaa0 Freed by task 239: kfree+0x18f/0x520 devicereleasedriverinternal+0x388/0x540 unbindstore+0xd9/0x100
This lands in the timer core rather than vtimer() itself because the embedded timerlist is being walked after its containing struct vudc has already been freed. The underlying lifetime bug is the same one Zheng reported.
With vstoptimer() called from vudcremove() and the timer deleted synchronously, the same harness completed 5000 bind/unbind iterations with no KASAN report.
Affected Software
Remediation
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In usbip vudc, call v_stop_timer() from vudc_remove() and delete the timer synchronously before freeing the containing struct vudc.
Event History
Frequently Asked Questions
Which systems are exposed to this issue?
Systems using the Linux kernel USB/IP virtual USB device controller (vudc) are exposed. The reported reproduction uses CONFIG_USBIP_VUDC=y; systems without that component enabled are not shown to be affected by the provided information.
What conditions are required to trigger the race?
A timer must be started through usbip_sockfd_store(), then the vudc device must be unbound or removed while that timer remains pending or is executing. The reported test repeatedly writes a socket file descriptor, closes the socket pair, and unbinds and rebinds usbip-vudc.0.
What is the likely impact if the race is triggered?
The removal path can free the vudc structure while its timer still references it, causing a slab use-after-free. The supplied severity vector rates confidentiality, integrity, and availability impact as high, with local low-privilege access required.
How can administrators determine whether they are affected?
Check whether the running kernel has USB/IP vudc support enabled, particularly CONFIG_USBIP_VUDC. The provided evidence identifies KASAN slab-use-after-free reports in __run_timer_base during vudc removal as an indicator that the race has been triggered.