CVE-2026-63905

Summary

In the Linux kernel, the following vulnerability has been resolved:

usbip: vudc: Fix use after free bug in vudc_remove due to race condition

This patch follows up Zheng Wang's 2023 report of a use-after-free in vudc_remove(). 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 vudc_probe(), v_init_timer() binds udc->tr_timer.timer to v_timer(). usbip_sockfd_store() starts the timer via v_start_timer()/v_kick_timer(). vudc_remove() can then free the containing struct vudc while the timer is still pending or executing.

KASAN confirms the race on an unpatched x86_64 QEMU guest with CONFIG_KASAN=y, CONFIG_USBIP_VUDC=y, CONFIG_USB_ZERO=y, and a tight loop that repeatedly writes a socket fd to usbip_sockfd, closes the socket pair, and unbinds/rebinds usbip-vudc.0:

BUG: KASAN: slab-use-after-free in __run_timer_base.part.0+0x8ba/0x8e0 Write of size 8 at addr ffff888001b80740 by task trigger_and_unb/239 Allocated by task 239: vudc_probe+0x4d/0xaa0 Freed by task 239: kfree+0x18f/0x520 device_release_driver_internal+0x388/0x540 unbind_store+0xd9/0x100

This lands in the timer core rather than v_timer() itself because the embedded timer_list is being walked after its containing struct vudc has already been freed. The underlying lifetime bug is the same one Zheng reported.

With v_stop_timer() called from vudc_remove() and the timer deleted synchronously, the same harness completed 5000 bind/unbind iterations with no KASAN report.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/61704e5cf9cd7464b510eb606e7e2978b1160a64
• https://git.kernel.org/stable/c/dcc1c90b28b28b7c493547506297e78653f81952
• https://git.kernel.org/stable/c/1036ac6148995feaf486014d32bf26bf993c06a9
• https://git.kernel.org/stable/c/a0638db2340ee053ab0450656a763fd111475e54
• https://git.kernel.org/stable/c/d07ed707467ce05ea9c03412d0c5ee9d0fe386a6
• https://git.kernel.org/stable/c/88d459e5b5a46da1ef9fd6f52d9439343edeec88
• https://git.kernel.org/stable/c/207bf80362df3fce8ebc9723351dcb1bc6d9ed0f
• https://git.kernel.org/stable/c/d96209626a29ea64666be98c30b30ac82e5f1be6

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