general protection fault in vmk80xx_write_packet

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    7829a896 usb-fuzzer: main usb gadget fuzzer driver
git tree:       https://github.com/google/kasan.git usb-fuzzer
console output: https://syzkaller.appspot.com/x/log.txt?x=126dd493a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f6d4561982f71f63
dashboard link: https://syzkaller.appspot.com/bug?extid=009f546aa1370056b1c2
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1684570ba00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=132c91f5a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+009f546aa1370056b1c2@xxxxxxxxxxxxxxxxxxxxxxxxx

usb 1-1: config 0 interface 160 has no altsetting 0
usb 1-1: New USB device found, idVendor=10cf, idProduct=5501,  
bcdDevice=eb.5b
usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
usb 1-1: config 0 descriptor??
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
CPU: 1 PID: 21 Comm: kworker/1:1 Not tainted 5.2.0-rc6+ #13
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: usb_hub_wq hub_event
RIP: 0010:vmk80xx_write_packet+0x75/0x260  
drivers/staging/comedi/drivers/vmk80xx.c:204
Code: 48 8d 7b 68 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 d3 01 00 00 48 b8  
00 00 00 00 00 fc ff df 4c 8b 6b 68 4c 89 ea 48 c1 ea 03 <0f> b6 04 02 4c  
89 ea 83 e2 07 38 d0 7f 08 84 c0 0f 85 84 01 00 00
RSP: 0018:ffff8881d9eff1b0 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffff8881d4f596c0 RCX: 0000000000000000
RDX: 0000000000000002 RSI: ffffffff847cda93 RDI: ffff8881d4f59728
RBP: ffff8881cfc79900 R08: ffff8881d9e36000 R09: 0000000000000010
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8881c5d84c80
R13: 0000000000000010 R14: 0000000000000000 R15: ffff8881d2690128
FS:  0000000000000000(0000) GS:ffff8881db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9c904c4000 CR3: 00000001d2b52000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 vmk80xx_reset_device drivers/staging/comedi/drivers/vmk80xx.c:226 [inline]
 vmk80xx_auto_attach+0x13b1/0x17c0  
drivers/staging/comedi/drivers/vmk80xx.c:814
 comedi_auto_config+0x16e/0x250 drivers/staging/comedi/drivers.c:1067
 usb_probe_interface+0x305/0x7a0 drivers/usb/core/driver.c:361
 really_probe+0x281/0x660 drivers/base/dd.c:509
 driver_probe_device+0x104/0x210 drivers/base/dd.c:670
 __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:777
 bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454
 __device_attach+0x217/0x360 drivers/base/dd.c:843
 bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514
 device_add+0xae6/0x16f0 drivers/base/core.c:2111
 usb_set_configuration+0xdf6/0x1670 drivers/usb/core/message.c:2023
 generic_probe+0x9d/0xd5 drivers/usb/core/generic.c:210
 usb_probe_device+0x99/0x100 drivers/usb/core/driver.c:266
 really_probe+0x281/0x660 drivers/base/dd.c:509
 driver_probe_device+0x104/0x210 drivers/base/dd.c:670
 __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:777
 bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454
 __device_attach+0x217/0x360 drivers/base/dd.c:843
 bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514
 device_add+0xae6/0x16f0 drivers/base/core.c:2111
 usb_new_device.cold+0x8c1/0x1016 drivers/usb/core/hub.c:2534
 hub_port_connect drivers/usb/core/hub.c:5089 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5204 [inline]
 port_event drivers/usb/core/hub.c:5350 [inline]
 hub_event+0x1ada/0x3590 drivers/usb/core/hub.c:5432
 process_one_work+0x905/0x1570 kernel/workqueue.c:2269
 worker_thread+0x96/0xe20 kernel/workqueue.c:2415
 kthread+0x30b/0x410 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Modules linked in:
---[ end trace 8425c817ce1da187 ]---


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches