KMSAN: kernel-infoleak in video_usercopy

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 0a602458c72c kmsan: random: another take at unpoisoning CR..
git tree: kmsan
console output: https://syzkaller.appspot.com/x/log.txt?x=12f2cd5d400000
kernel config: https://syzkaller.appspot.com/x/.config?x=9b071100dcf8e641
dashboard link: https://syzkaller.appspot.com/bug?extid=4f021cf3697781dbd9fb
compiler: clang version 8.0.0 (trunk 348261)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15d6b21b400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17f15885400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4f021c...@syzkaller.appspotmail.com

==================================================================
BUG: KMSAN: kernel-infoleak in _copy_to_user+0x1a4/0x250 lib/usercopy.c:32
CPU: 0 PID: 6254 Comm: syz-executor456 Not tainted 4.20.0-rc5+ #2
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+0x1c9/0x220 lib/dump_stack.c:113
kmsan_report+0x12d/0x290 mm/kmsan/kmsan.c:682
kmsan_internal_check_memory+0x334/0xa60 mm/kmsan/kmsan.c:742
kmsan_copy_to_user+0x8d/0xa0 mm/kmsan/kmsan_hooks.c:604
_copy_to_user+0x1a4/0x250 lib/usercopy.c:32
copy_to_user include/linux/uaccess.h:177 [inline]
video_usercopy+0x16c9/0x17d0 drivers/media/v4l2-core/v4l2-ioctl.c:3066
video_ioctl2+0x9f/0xb0 drivers/media/v4l2-core/v4l2-ioctl.c:3079
v4l2_ioctl+0x23f/0x270 drivers/media/v4l2-core/v4l2-dev.c:364
do_vfs_ioctl+0xf36/0x2d30 fs/ioctl.c:46
ksys_ioctl fs/ioctl.c:713 [inline]
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl+0x1da/0x270 fs/ioctl.c:718
__x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:718
do_syscall_64+0xcd/0x110 arch/x86/entry/common.c:291
entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x445659
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:00007ff7a472ada8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dac28 RCX: 0000000000445659
RDX: 0000000020000000 RSI: 0000000080885659 RDI: 0000000000000003
RBP: 00000000006dac20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac2c
R13: 6469762f7665642f R14: 00007ff7a472b9c0 R15: 00000000006dad2c

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:247 [inline]
kmsan_save_stack mm/kmsan/kmsan.c:262 [inline]
kmsan_internal_chain_origin+0x162/0x260 mm/kmsan/kmsan.c:470
kmsan_memcpy_memmove_metadata+0x1a9/0xf30 mm/kmsan/kmsan.c:345
kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:363
__msan_memcpy+0x61/0x70 mm/kmsan/kmsan_instr.c:148
__v4l2_event_dequeue+0x2f8/0x730 drivers/media/v4l2-core/v4l2-event.c:54
v4l2_event_dequeue+0x41c/0x560 drivers/media/v4l2-core/v4l2-event.c:81
v4l_dqevent+0xba/0xe0 drivers/media/v4l2-core/v4l2-ioctl.c:2427
__video_do_ioctl+0x1975/0x1fc0 drivers/media/v4l2-core/v4l2-ioctl.c:2853
video_usercopy+0x8ae/0x17d0 drivers/media/v4l2-core/v4l2-ioctl.c:3035
video_ioctl2+0x9f/0xb0 drivers/media/v4l2-core/v4l2-ioctl.c:3079
v4l2_ioctl+0x23f/0x270 drivers/media/v4l2-core/v4l2-dev.c:364
do_vfs_ioctl+0xf36/0x2d30 fs/ioctl.c:46
ksys_ioctl fs/ioctl.c:713 [inline]
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl+0x1da/0x270 fs/ioctl.c:718
__x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:718
do_syscall_64+0xcd/0x110 arch/x86/entry/common.c:291
entry_SYSCALL_64_after_hwframe+0x63/0xe7

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:247 [inline]
kmsan_save_stack mm/kmsan/kmsan.c:262 [inline]
kmsan_internal_chain_origin+0x162/0x260 mm/kmsan/kmsan.c:470
kmsan_memcpy_memmove_metadata+0x1a9/0xf30 mm/kmsan/kmsan.c:345
kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:363
__msan_memcpy+0x61/0x70 mm/kmsan/kmsan_instr.c:148
__v4l2_event_queue_fh+0xd2d/0x1260 drivers/media/v4l2-core/v4l2-event.c:145
v4l2_event_queue_fh+0x1a1/0x270 drivers/media/v4l2-core/v4l2-event.c:185
v4l2_ctrl_add_event+0x952/0xc20 drivers/media/v4l2-core/v4l2-ctrls.c:4099
v4l2_event_subscribe+0xf75/0x1240 drivers/media/v4l2-core/v4l2-event.c:251
v4l2_ctrl_subscribe_event+0xb6/0x110
drivers/media/v4l2-core/v4l2-ctrls.c:4156
v4l_subscribe_event+0x9e/0xc0 drivers/media/v4l2-core/v4l2-ioctl.c:2433
__video_do_ioctl+0x1975/0x1fc0 drivers/media/v4l2-core/v4l2-ioctl.c:2853
video_usercopy+0x8ae/0x17d0 drivers/media/v4l2-core/v4l2-ioctl.c:3035
video_ioctl2+0x9f/0xb0 drivers/media/v4l2-core/v4l2-ioctl.c:3079
v4l2_ioctl+0x23f/0x270 drivers/media/v4l2-core/v4l2-dev.c:364
do_vfs_ioctl+0xf36/0x2d30 fs/ioctl.c:46
ksys_ioctl fs/ioctl.c:713 [inline]
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl+0x1da/0x270 fs/ioctl.c:718
__x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:718
do_syscall_64+0xcd/0x110 arch/x86/entry/common.c:291
entry_SYSCALL_64_after_hwframe+0x63/0xe7

Local variable description: ----ev@v4l2_ctrl_add_event
Variable was created at:
v4l2_ctrl_add_event+0x6e/0xc20 drivers/media/v4l2-core/v4l2-ctrls.c:4080
v4l2_event_subscribe+0xf75/0x1240 drivers/media/v4l2-core/v4l2-event.c:251

Bytes 44-71 of 136 are uninitialized
Memory access of size 136 starts at ffff8881bcc903c0
Data copied to user address 0000000020000000
==================================================================


---
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 syzk...@googlegroups.com.

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