general protection fault in gigaset_probe

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    6a3599ce 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=11865a5c600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=700ca426ab83faae
dashboard link: https://syzkaller.appspot.com/bug?extid=35b1c403a14f5c89eba7
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14004a7c600000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=139068cc600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+35b1c403a14f5c89eba7@xxxxxxxxxxxxxxxxxxxxxxxxx

usb 1-1: new high-speed USB device number 2 using dummy_hcd
usb 1-1: New USB device found, idVendor=0681, idProduct=0009,  
bcdDevice=ed.98
usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
usb 1-1: config 0 descriptor??
usb 1-1: gigaset_probe: Device matched ... !
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: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.2.0-rc6+ #15
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: usb_hub_wq hub_event
RIP: 0010:gigaset_probe.cold+0x25d/0xd31  
drivers/isdn/gigaset/usb-gigaset.c:707
Code: e0 2a 80 3c 02 00 74 0a 48 8b 7c 24 08 e8 26 e6 1c fd 4d 8b 6f 18 ba  
ff ff 37 00 48 c1 e2 2a 49 8d 7d 04 48 89 f8 48 c1 e8 03 <0f> b6 0c 10 49  
8d 45 05 48 89 c6 48 c1 ee 03 0f b6 14 16 48 89 fe
RSP: 0018:ffff8881d9e0f2e0 EFLAGS: 00010247
RAX: 0000000000000000 RBX: ffff8881c6820880 RCX: ffffffff81ddae1d
RDX: dffffc0000000000 RSI: ffffffff83456ce6 RDI: 0000000000000004
RBP: ffff8881c68200a0 R08: ffff8881d9df9800 R09: ffffed103b3c1e43
R10: ffffed103b3c1e42 R11: 0000000000000003 R12: ffff8881d0f4df00
R13: 0000000000000000 R14: ffff8881d41aa100 R15: ffff8881d244f488
FS:  0000000000000000(0000) GS:ffff8881db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f52a049b000 CR3: 00000001d342f000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 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+0x6a4/0xe61 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+0x1abd/0x3550 drivers/usb/core/hub.c:5441
 process_one_work+0x905/0x1570 kernel/workqueue.c:2269
 worker_thread+0x96/0xe20 kernel/workqueue.c:2415


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