KASAN: null-ptr-deref Read in zr364xx_vidioc_querycap

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    43151d6c usb-fuzzer: main usb gadget fuzzer driver
git tree:       https://github.com/google/kasan/tree/usb-fuzzer
console output: https://syzkaller.appspot.com/x/log.txt?x=139fc338a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4183eeef650d1234
dashboard link: https://syzkaller.appspot.com/bug?extid=66010012fd4c531a1a96
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1661d17ca00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=177d7262a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+66010012fd4c531a1a96@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: null-ptr-deref in read_word_at_a_time+0xe/0x20  
include/linux/compiler.h:274
Read of size 1 at addr 0000000000000000 by task v4l_id/5287

CPU: 1 PID: 5287 Comm: v4l_id Not tainted 5.1.0-rc3-319004-g43151d6 #6
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0xe8/0x16e lib/dump_stack.c:113
 kasan_report.cold+0x5/0x3c mm/kasan/report.c:321
 read_word_at_a_time+0xe/0x20 include/linux/compiler.h:274
 strscpy+0x8a/0x280 lib/string.c:207
 zr364xx_vidioc_querycap+0xb5/0x210 drivers/media/usb/zr364xx/zr364xx.c:706
 v4l_querycap+0x12b/0x340 drivers/media/v4l2-core/v4l2-ioctl.c:1062
 __video_do_ioctl+0x5bb/0xb40 drivers/media/v4l2-core/v4l2-ioctl.c:2874
 video_usercopy+0x44e/0xf00 drivers/media/v4l2-core/v4l2-ioctl.c:3056
 v4l2_ioctl+0x14e/0x1a0 drivers/media/v4l2-core/v4l2-dev.c:364
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0xced/0x12f0 fs/ioctl.c:696
 ksys_ioctl+0xa0/0xc0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x74/0xb0 fs/ioctl.c:718
 do_syscall_64+0xcf/0x4f0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f3b56d8b347
Code: 90 90 90 48 8b 05 f1 fa 2a 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff  
ff c3 90 90 90 90 90 90 90 90 90 90 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff  
ff 73 01 c3 48 8b 0d c1 fa 2a 00 31 d2 48 29 c2 64
RSP: 002b:00007ffe005d5d68 EFLAGS: 00000202 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f3b56d8b347
RDX: 00007ffe005d5d70 RSI: 0000000080685600 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000400884
R13: 00007ffe005d5ec0 R14: 0000000000000000 R15: 0000000000000000
==================================================================


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