wifi: ath10k: avoid NULL pointer error during sdio remove

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

wifi: ath10k: avoid NULL pointer error during sdio remove

When running 'rmmod ath10k', ath10k_sdio_remove() will free sdio

workqueue by destroy_workqueue(). But if CONFIG_INIT_ON_FREE_DEFAULT_ON

is set to yes, kernel panic will happen:

Call trace:

destroy_workqueue+0x1c/0x258

ath10k_sdio_remove+0x84/0x94

sdio_bus_remove+0x50/0x16c

device_release_driver_internal+0x188/0x25c

device_driver_detach+0x20/0x2c

This is because during 'rmmod ath10k', ath10k_sdio_remove() will call

ath10k_core_destroy() before destroy_workqueue(). wiphy_dev_release()

will finally be called in ath10k_core_destroy(). This function will free

struct cfg80211_registered_device *rdev and all its members, including

wiphy, dev and the pointer of sdio workqueue. Then the pointer of sdio

workqueue will be set to NULL due to CONFIG_INIT_ON_FREE_DEFAULT_ON.

After device release, destroy_workqueue() will use NULL pointer then the

kernel panic happen.

Call trace:

ath10k_sdio_remove

->ath10k_core_unregister

……

->ath10k_core_stop

->ath10k_hif_stop

->ath10k_sdio_irq_disable

->ath10k_hif_power_down

->del_timer_sync(&ar_sdio->sleep_timer)

->ath10k_core_destroy

->ath10k_mac_destroy

->ieee80211_free_hw

->wiphy_free

……

->wiphy_dev_release

->destroy_workqueue

Need to call destroy_workqueue() before ath10k_core_destroy(), free

the work queue buffer first and then free pointer of work queue by

ath10k_core_destroy(). This order matches the error path order in

ath10k_sdio_probe().

No work will be queued on sdio workqueue between it is destroyed and

ath10k_core_destroy() is called. Based on the call_stack above, the

reason is:

Only ath10k_sdio_sleep_timer_handler(), ath10k_sdio_hif_tx_sg() and

ath10k_sdio_irq_disable() will queue work on sdio workqueue.

Sleep timer will be deleted before ath10k_core_destroy() in

ath10k_hif_power_down().

ath10k_sdio_irq_disable() only be called in ath10k_hif_stop().

ath10k_core_unregister() will call ath10k_hif_power_down() to stop hif

bus, so ath10k_sdio_hif_tx_sg() won't be called anymore.

Tested-on: QCA6174 hw3.2 SDIO WLAN.RMH.4.4.1-00189