KMSAN: uninit-value in video_usercopy

KMSAN: uninit-value in video_usercopy

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    14525656 compiler.h: reinstate missing KMSAN_INIT
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=15be8380900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c534a9fad6323722
dashboard link: https://syzkaller.appspot.com/bug?extid=79d751604cb6f29fbf59
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17eb93d0900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=116da33b100000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+79d751604cb6f29fbf59@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in kmsan_check_memory+0xd/0x10 mm/kmsan/kmsan_hooks.c:428
CPU: 0 PID: 8471 Comm: syz-executor794 Not tainted 5.8.0-rc5-syzkaller #0
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+0x1df/0x240 lib/dump_stack.c:118
 kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:121
 kmsan_internal_check_memory+0x238/0x3d0 mm/kmsan/kmsan.c:423
 kmsan_check_memory+0xd/0x10 mm/kmsan/kmsan_hooks.c:428
 instrument_copy_to_user include/linux/instrumented.h:91 [inline]
 _copy_to_user+0x100/0x1d0 lib/usercopy.c:30
 copy_to_user include/linux/uaccess.h:161 [inline]
 video_put_user drivers/media/v4l2-core/v4l2-ioctl.c:3226 [inline]
 video_usercopy+0x248a/0x2c00 drivers/media/v4l2-core/v4l2-ioctl.c:3325
 video_ioctl2+0x9f/0xb0 drivers/media/v4l2-core/v4l2-ioctl.c:3335
 v4l2_ioctl+0x23f/0x270 drivers/media/v4l2-core/v4l2-dev.c:360
 vfs_ioctl fs/ioctl.c:48 [inline]
 ksys_ioctl fs/ioctl.c:753 [inline]
 __do_sys_ioctl fs/ioctl.c:762 [inline]
 __se_sys_ioctl+0x2e9/0x410 fs/ioctl.c:760
 __x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:760
 do_syscall_64+0xb0/0x150 arch/x86/entry/common.c:386
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x444009
Code: Bad RIP value.
RSP: 002b:00007ffd83706aa8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 0000000000444009
RDX: 0000000020000100 RSI: 00000000c0505611 RDI: 0000000000000003
RBP: 00000000006ce018 R08: 00000000004002e0 R09: 00000000004002e0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401c90
R13: 0000000000401d20 R14: 0000000000000000 R15: 0000000000000000

Local variable ----vb32.i@video_usercopy created at:
 video_put_user drivers/media/v4l2-core/v4l2-ioctl.c:3210 [inline]
 video_usercopy+0x20bd/0x2c00 drivers/media/v4l2-core/v4l2-ioctl.c:3325
 video_put_user drivers/media/v4l2-core/v4l2-ioctl.c:3210 [inline]
 video_usercopy+0x20bd/0x2c00 drivers/media/v4l2-core/v4l2-ioctl.c:3325

Bytes 52-55 of 80 are uninitialized
Memory access of size 80 starts at ffffa41d80dcfce0
=====================================================


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