KASAN: stack-out-of-bounds Write in ath9k_hif_usb_rx_cb

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    0fa84af8 Merge tag 'usb-serial-5.7-rc1' of https://git.ker..
git tree:       https://github.com/google/kasan.git usb-fuzzer
console output: https://syzkaller.appspot.com/x/log.txt?x=159a0583e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a782c087b1f425c6
dashboard link: https://syzkaller.appspot.com/bug?extid=d403396d4df67ad0bd5f
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=177a266de00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1579f947e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+d403396d4df67ad0bd5f@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: stack-out-of-bounds in ath9k_hif_usb_rx_stream drivers/net/wireless/ath/ath9k/hif_usb.c:626 [inline]
BUG: KASAN: stack-out-of-bounds in ath9k_hif_usb_rx_cb+0xdf6/0xf70 drivers/net/wireless/ath/ath9k/hif_usb.c:666
Write of size 8 at addr ffff8881db309a28 by task swapper/1/0

CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.6.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0xef/0x16e lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xd3/0x314 mm/kasan/report.c:374
 __kasan_report.cold+0x37/0x77 mm/kasan/report.c:506
 kasan_report+0xe/0x20 mm/kasan/common.c:641
 ath9k_hif_usb_rx_stream drivers/net/wireless/ath/ath9k/hif_usb.c:626 [inline]
 ath9k_hif_usb_rx_cb+0xdf6/0xf70 drivers/net/wireless/ath/ath9k/hif_usb.c:666
 __usb_hcd_giveback_urb+0x1f2/0x470 drivers/usb/core/hcd.c:1648
 usb_hcd_giveback_urb+0x368/0x420 drivers/usb/core/hcd.c:1713
 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


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