The skb is consumed by htc_send_epid, so it needn't release again.

The case reported by syzbot:

https://lore.kernel.org/linux-usb/000000000000590f6b05a1c05d15@google.com
usb 1-1: ath9k_htc: Firmware ath9k_htc/htc_9271-1.4.0.fw requested
usb 1-1: ath9k_htc: Transferred FW: ath9k_htc/htc_9271-1.4.0.fw, size:
51008
usb 1-1: Service connection timeout for: 256
==================================================================
BUG: KASAN: use-after-free in atomic_read
include/asm-generic/atomic-instrumented.h:26 [inline]
BUG: KASAN: use-after-free in refcount_read include/linux/refcount.h:134
[inline]
BUG: KASAN: use-after-free in skb_unref include/linux/skbuff.h:1042
[inline]
BUG: KASAN: use-after-free in kfree_skb+0x32/0x3d0 net/core/skbuff.c:692
Read of size 4 at addr ffff8881d0957994 by task kworker/1:2/83

Call Trace:
kfree_skb+0x32/0x3d0 net/core/skbuff.c:692
htc_connect_service.cold+0xa9/0x109
drivers/net/wireless/ath/ath9k/htc_hst.c:282
ath9k_wmi_connect+0xd2/0x1a0 drivers/net/wireless/ath/ath9k/wmi.c:265
ath9k_init_htc_services.constprop.0+0xb4/0x650
drivers/net/wireless/ath/ath9k/htc_drv_init.c:146
ath9k_htc_probe_device+0x25a/0x1d80
drivers/net/wireless/ath/ath9k/htc_drv_init.c:959
ath9k_htc_hw_init+0x31/0x60
drivers/net/wireless/ath/ath9k/htc_hst.c:501
ath9k_hif_usb_firmware_cb+0x26b/0x500
drivers/net/wireless/ath/ath9k/hif_usb.c:1187
request_firmware_work_func+0x126/0x242
drivers/base/firmware_loader/main.c:976
process_one_work+0x94b/0x1620 kernel/workqueue.c:2264
worker_thread+0x96/0xe20 kernel/workqueue.c:2410
kthread+0x318/0x420 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 83:
kmem_cache_alloc_node+0xdc/0x330 mm/slub.c:2814
__alloc_skb+0xba/0x5a0 net/core/skbuff.c:198
alloc_skb include/linux/skbuff.h:1081 [inline]
htc_connect_service+0x2cc/0x840
drivers/net/wireless/ath/ath9k/htc_hst.c:257
ath9k_wmi_connect+0xd2/0x1a0 drivers/net/wireless/ath/ath9k/wmi.c:265
ath9k_init_htc_services.constprop.0+0xb4/0x650
drivers/net/wireless/ath/ath9k/htc_drv_init.c:146
ath9k_htc_probe_device+0x25a/0x1d80
drivers/net/wireless/ath/ath9k/htc_drv_init.c:959
ath9k_htc_hw_init+0x31/0x60
drivers/net/wireless/ath/ath9k/htc_hst.c:501
ath9k_hif_usb_firmware_cb+0x26b/0x500
drivers/net/wireless/ath/ath9k/hif_usb.c:1187
request_firmware_work_func+0x126/0x242
drivers/base/firmware_loader/main.c:976
process_one_work+0x94b/0x1620 kernel/workqueue.c:2264
worker_thread+0x96/0xe20 kernel/workqueue.c:2410
kthread+0x318/0x420 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Freed by task 0:
kfree_skb+0x102/0x3d0 net/core/skbuff.c:690
ath9k_htc_txcompletion_cb+0x1f8/0x2b0
drivers/net/wireless/ath/ath9k/htc_hst.c:356
hif_usb_regout_cb+0x10b/0x1b0
drivers/net/wireless/ath/ath9k/hif_usb.c:90
__usb_hcd_giveback_urb+0x29a/0x550 drivers/usb/core/hcd.c:1650
usb_hcd_giveback_urb+0x368/0x420 drivers/usb/core/hcd.c:1716
dummy_timer+0x1258/0x32ae drivers/usb/gadget/udc/dummy_hcd.c:1966
call_timer_fn+0x195/0x6f0 kernel/time/timer.c:1404
expire_timers kernel/time/timer.c:1449 [inline]
__run_timers kernel/time/timer.c:1773 [inline]
__run_timers kernel/time/timer.c:1740 [inline]
run_timer_softirq+0x5f9/0x1500 kernel/time/timer.c:1786
__do_softirq+0x21e/0x950 kernel/softirq.c:292

Reported-and-tested-by: syzbot+9505af1ae303dabdc646@syzkaller.appspotmail.com
Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200404041838.10426-2-hqjagain@gmail.com