wifi: ath9k: hif_usb: don't dereference hif_dev after re-arming firmware request

Overview

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

wifi: ath9k: hif_usb: don't dereference hif_dev after re-arming firmware request

ath9k_hif_request_firmware() re-arms an asynchronous firmware load via request_firmware_nowait(), passing hif_dev as the completion context, and then still dereferences hif_dev:

dev_info(&hif_dev->udev->dev, "ath9k_htc: Firmware %s requested\n",
	 hif_dev->fw_name);

The re-armed callback ath9k_hif_usb_firmware_cb() runs on the "events" workqueue and, when the firmware is missing, walks the retry chain into ath9k_hif_usb_firmware_fail() -> complete_all(&hif_dev->fw_done). That releases the wait_for_completion(&hif_dev->fw_done) in a concurrent ath9k_hif_usb_disconnect(), which then kfree()s hif_dev. The trailing dev_info() in the frame that re-armed the request can therefore read freed memory (hif_dev->udev, the first field of struct hif_device_usb):

BUG: KASAN: slab-use-after-free in ath9k_hif_request_firmware Read of size 8 ... by task kworker/... ath9k_hif_request_firmware ath9k_hif_usb_firmware_cb drivers/net/wireless/ath/ath9k/hif_usb.c:1247 request_firmware_work_func Allocated by ...: ath9k_hif_usb_probe drivers/net/wireless/ath/ath9k/hif_usb.c Freed by ...: ath9k_hif_usb_disconnect -> kfree drivers/net/wireless/ath/ath9k/hif_usb.c

The fw_done barrier only makes disconnect wait for the firmware chain to terminate; it does not protect the outer ath9k_hif_request_firmware() frame that re-armed the request and keeps touching hif_dev afterwards.

Drop the post-request dev_info(): it is the only use of hif_dev after the async request is armed, and it is purely informational (the dev_err() on the failure path runs only when request_firmware_nowait() did not arm a callback, so hif_dev is still alive there).

This was first reported by syzbot as a single, non-reproduced crash that was later auto-obsoleted, and was independently rediscovered by the reFuzz fuzzer, which produced a C reproducer (USB-gadget connect/disconnect of an ath9k_htc device whose firmware download fails). The vulnerable code is unchanged and still present in v7.1-rc6, where the slab-use-after-free reproduces under KASAN once the (sub-microsecond) race window is widened.

Affected

• Linux >= e904cf6fe23022cde4e0ea9d41601411a315a3dc < 47ed81aaa7f94d9808f4719e78a760c2ec1e6c86
• Linux >= e904cf6fe23022cde4e0ea9d41601411a315a3dc < 48de0c6952192b0771fca468df4364d11ec74ad9
• Linux >= e904cf6fe23022cde4e0ea9d41601411a315a3dc < 063497cc9f320ab71a7a937c3bc0a23e630aefe2
• Linux >= e904cf6fe23022cde4e0ea9d41601411a315a3dc < 7f184ca38a90889f3f6665ff96748b95da39dbee
• Linux >= e904cf6fe23022cde4e0ea9d41601411a315a3dc < 10b0ce629123a3737b4eda50188f73bb7be7b68b
• Linux >= e904cf6fe23022cde4e0ea9d41601411a315a3dc < 48a69cedde7388294e4ea6fd804156cd62bc04fc
• Linux >= e904cf6fe23022cde4e0ea9d41601411a315a3dc < 7c9046d92c4b9789c9d9d775e4fd5f34be64cb0a
• Linux >= e904cf6fe23022cde4e0ea9d41601411a315a3dc < dad9f96945d77ecd4708f730c06ef54dcd8cc057
• Linux 4.4

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.