divide error in cdc_ncm_update_rxtx_max

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    f0df5c1b 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=14cd1459600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5c6633fa4ed00be5
dashboard link: https://syzkaller.appspot.com/bug?extid=ce366e2b8296e25d84f5
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12b4dd85600000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=179b7fc1600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+ce366e2b8296e25d84f5@xxxxxxxxxxxxxxxxxxxxxxxxx

cdc_ncm 1-1:1.0: dwNtbInMaxSize=0 is too small. Using 2048
cdc_ncm 1-1:1.0: setting rx_max = 2048
cdc_ncm 1-1:1.0: setting tx_max = 16384
divide error: 0000 [#1] SMP KASAN
CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.3.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: usb_hub_wq hub_event
RIP: 0010:cdc_ncm_update_rxtx_max+0xc6e/0xef0 drivers/net/usb/cdc_ncm.c:419
Code: e0 07 38 c2 0f 9e c1 84 d2 0f 95 c0 84 c1 0f 85 35 02 00 00 0f b7 5b  
04 81 e3 ff 07 00 00 e8 29 47 f7 fd 31 d2 44 89 e0 31 ff <f7> f3 41 89 d5  
89 d6 e8 86 48 f7 fd 45 85 ed 0f 85 17 f7 ff ff e8
RSP: 0018:ffff8881da20f030 EFLAGS: 00010246
RAX: 0000000000004000 RBX: 0000000000000000 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffffffff83469377 RDI: 0000000000000000
RBP: ffff8881c7ba0000 R08: ffff8881da1f9800 R09: ffffed103b645d58
R10: ffffed103b645d57 R11: ffff8881db22eabf R12: 0000000000004000
R13: 0000000000000000 R14: ffff8881d35f3dc0 R15: ffff8881d2a70f00
FS:  0000000000000000(0000) GS:ffff8881db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f1059879000 CR3: 00000001d49db000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 cdc_ncm_setup drivers/net/usb/cdc_ncm.c:667 [inline]
 cdc_ncm_bind_common+0x1005/0x2570 drivers/net/usb/cdc_ncm.c:924
 cdc_ncm_bind+0x7c/0x1c0 drivers/net/usb/cdc_ncm.c:1038
 usbnet_probe+0xb43/0x23cf drivers/net/usb/usbnet.c:1722
 usb_probe_interface+0x305/0x7a0 drivers/usb/core/driver.c:361
 really_probe+0x281/0x6d0 drivers/base/dd.c:548
 driver_probe_device+0x101/0x1b0 drivers/base/dd.c:721
 __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:828
 bus_for_each_drv+0x162/0x1e0 drivers/base/bus.c:454
 __device_attach+0x217/0x360 drivers/base/dd.c:894
 bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514
 device_add+0xae6/0x16f0 drivers/base/core.c:2165
 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+0x281/0x6d0 drivers/base/dd.c:548
 driver_probe_device+0x101/0x1b0 drivers/base/dd.c:721
 __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:828
 bus_for_each_drv+0x162/0x1e0 drivers/base/bus.c:454
 __device_attach+0x217/0x360 drivers/base/dd.c:894
 bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514
 device_add+0xae6/0x16f0 drivers/base/core.c:2165
 usb_new_device.cold+0x6a4/0xe79 drivers/usb/core/hub.c:2536
 hub_port_connect drivers/usb/core/hub.c:5098 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
 port_event drivers/usb/core/hub.c:5359 [inline]
 hub_event+0x1b5c/0x3640 drivers/usb/core/hub.c:5441
 process_one_work+0x92b/0x1530 kernel/workqueue.c:2269
 worker_thread+0x96/0xe20 kernel/workqueue.c:2415
 kthread+0x318/0x420 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Modules linked in:
---[ end trace ab75cc10e099d8e9 ]---
RIP:


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