In ath9k_hif_usb_rx_cb interface number is assumed to be 0.
usb_ifnum_to_if(urb->dev, 0)
But it isn't always true.

The case reported by syzbot:
https://lore.kernel.org/linux-usb/000000000000666c9c05a1c05d12@google.com
usb 2-1: new high-speed USB device number 2 using dummy_hcd
usb 2-1: config 1 has an invalid interface number: 2 but max is 0
usb 2-1: config 1 has no interface number 0
usb 2-1: New USB device found, idVendor=0cf3, idProduct=9271, bcdDevice=
1.08
usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
general protection fault, probably for non-canonical address
0xdffffc0000000015: 0000 [#1] SMP KASAN
KASAN: null-ptr-deref in range [0x00000000000000a8-0x00000000000000af]
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.6.0-rc5-syzkaller #0

Call Trace
__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
invoke_softirq kernel/softirq.c:373 [inline]
irq_exit+0x178/0x1a0 kernel/softirq.c:413
exiting_irq arch/x86/include/asm/apic.h:546 [inline]
smp_apic_timer_interrupt+0x141/0x540 arch/x86/kernel/apic/apic.c:1146
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829

Reported-and-tested-by: syzbot+40d5d2e8a4680952f042@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/20200404041838.10426-6-hqjagain@gmail.com