From d96209626a29ea64666be98c30b30ac82e5f1be6 Mon Sep 17 00:00:00 2001 From: Michael Bommarito Date: Fri, 17 Apr 2026 12:35:52 -0400 Subject: [PATCH] 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. Fixes: b6a0ca111867 ("usbip: vudc: Add UDC specific ops") Cc: stable Reported-by: Zheng Wang Closes: https://lore.kernel.org/linux-usb/20230317100954.2626573-1-zyytlz.wz@163.com/ Signed-off-by: Michael Bommarito Acked-by: Shuah Khan Link: https://patch.msgid.link/20260417163552.807548-1-michael.bommarito@gmail.com Signed-off-by: Greg Kroah-Hartman --- drivers/usb/usbip/vudc_dev.c | 1 + drivers/usb/usbip/vudc_transfer.c | 3 ++- 2 files changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/usb/usbip/vudc_dev.c b/drivers/usb/usbip/vudc_dev.c index 90383107b660..c5f079c5a1ea 100644 --- a/drivers/usb/usbip/vudc_dev.c +++ b/drivers/usb/usbip/vudc_dev.c @@ -632,6 +632,7 @@ void vudc_remove(struct platform_device *pdev) { struct vudc *udc = platform_get_drvdata(pdev); + v_stop_timer(udc); usb_del_gadget_udc(&udc->gadget); cleanup_vudc_hw(udc); kfree(udc); diff --git a/drivers/usb/usbip/vudc_transfer.c b/drivers/usb/usbip/vudc_transfer.c index a4f02ea3e3ef..d4ce85c4c6a2 100644 --- a/drivers/usb/usbip/vudc_transfer.c +++ b/drivers/usb/usbip/vudc_transfer.c @@ -490,7 +490,8 @@ void v_stop_timer(struct vudc *udc) { struct transfer_timer *t = &udc->tr_timer; - /* timer itself will take care of stopping */ + /* Delete the timer synchronously before teardown frees udc. */ dev_dbg(&udc->pdev->dev, "timer stop"); + timer_delete_sync(&t->timer); t->state = VUDC_TR_STOPPED; }