WARNING: bad usercopy in fanotify_read

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    12ad143e Merge branch 'perf-urgent-for-linus' of git://git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12776f57200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e9d91b7192a5e96e
dashboard link: https://syzkaller.appspot.com/bug?extid=2c49971e251e36216d1f
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: amd64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1287516f200000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2c49971e251e36216d1f@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
Bad or missing usercopy whitelist? Kernel memory exposure attempt detected  
from SLAB object 'fanotify_event' (offset 40, size 8)!
WARNING: CPU: 1 PID: 7649 at mm/usercopy.c:78 usercopy_warn+0xeb/0x110  
mm/usercopy.c:78
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 7649 Comm: syz-executor381 Not tainted 5.0.0+ #17
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+0x172/0x1f0 lib/dump_stack.c:113
 panic+0x2cb/0x65c kernel/panic.c:214
 __warn.cold+0x20/0x45 kernel/panic.c:571
 report_bug+0x263/0x2b0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:179 [inline]
 fixup_bug arch/x86/kernel/traps.c:174 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
 do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:usercopy_warn+0xeb/0x110 mm/usercopy.c:78
Code: c8 e8 d9 88 c0 ff 4c 8b 45 c0 4d 89 e9 4c 89 e1 48 8b 55 c8 41 57 48  
89 de 48 c7 c7 e0 dc 74 87 ff 75 d0 41 56 e8 03 4b 93 ff <0f> 0b 48 83 c4  
18 e9 46 ff ff ff 49 c7 c5 e0 da 74 87 4d 89 ee 4d
RSP: 0018:ffff8880a417fb18 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffffffff8774dca0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815ad7b6 RDI: ffffed101482ff55
RBP: ffff8880a417fb70 R08: ffff888088d78580 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff8859408d
R13: ffffffff8775d500 R14: ffffffff8774db20 R15: 0000000000000008
 __check_heap_object+0x88/0xb3 mm/slab.c:4453
 check_heap_object mm/usercopy.c:238 [inline]
 __check_object_size mm/usercopy.c:284 [inline]
 __check_object_size+0x342/0x42f mm/usercopy.c:254
 check_object_size include/linux/thread_info.h:119 [inline]
 check_copy_size include/linux/thread_info.h:150 [inline]
 copy_to_user include/linux/uaccess.h:151 [inline]
 copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
 copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
 fanotify_read+0xde0/0x1430 fs/notify/fanotify/fanotify_user.c:362
 __vfs_read+0x8d/0x110 fs/read_write.c:416
 vfs_read+0x194/0x3e0 fs/read_write.c:452
 ksys_read+0xea/0x1f0 fs/read_write.c:578
 __do_sys_read fs/read_write.c:588 [inline]
 __se_sys_read fs/read_write.c:586 [inline]
 __x64_sys_read+0x73/0xb0 fs/read_write.c:586
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4456b9
Code: e8 6c b6 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 2b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fb296f31db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00000000006dac28 RCX: 00000000004456b9
RDX: 000000000000006b RSI: 0000000020000000 RDI: 0000000000000004
RBP: 00000000006dac20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac2c
R13: 00007ffd8eb3d16f R14: 00007fb296f329c0 R15: 20c49ba5e353f7cf
Kernel Offset: disabled
Rebooting in 86400 seconds..


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