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SubjectKMSAN: kernel-infoleak in compat_drm_wait_vblank
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Hello,

syzbot found the following issue on:

HEAD commit: 29ad81a1 arch/x86: add missing include to sparsemem.h
git tree: https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=111e6312d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=c8e3b38ca92283e
dashboard link: https://syzkaller.appspot.com/bug?extid=620cf21140fc7e772a5d
compiler: Debian clang version 11.0.1-2
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+620cf21140fc7e772a5d@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: kernel-infoleak in kmsan_copy_to_user+0x9c/0xb0 mm/kmsan/kmsan_hooks.c:249
CPU: 1 PID: 26999 Comm: syz-executor.2 Not tainted 5.11.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x21c/0x280 lib/dump_stack.c:120
kmsan_report+0xfb/0x1e0 mm/kmsan/kmsan_report.c:118
kmsan_internal_check_memory+0x484/0x520 mm/kmsan/kmsan.c:437
kmsan_copy_to_user+0x9c/0xb0 mm/kmsan/kmsan_hooks.c:249
instrument_copy_to_user include/linux/instrumented.h:121 [inline]
_copy_to_user+0x1ac/0x270 lib/usercopy.c:33
copy_to_user include/linux/uaccess.h:209 [inline]
compat_drm_wait_vblank+0x36f/0x450 drivers/gpu/drm/drm_ioc32.c:866
drm_compat_ioctl+0x3f6/0x590 drivers/gpu/drm/drm_ioc32.c:995
__do_compat_sys_ioctl fs/ioctl.c:842 [inline]
__se_compat_sys_ioctl+0x53d/0x1100 fs/ioctl.c:793
__ia32_compat_sys_ioctl+0x4a/0x70 fs/ioctl.c:793
do_syscall_32_irqs_on arch/x86/entry/common.c:79 [inline]
__do_fast_syscall_32+0x102/0x160 arch/x86/entry/common.c:141
do_fast_syscall_32+0x6a/0xc0 arch/x86/entry/common.c:166
do_SYSENTER_32+0x73/0x90 arch/x86/entry/common.c:209
entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7f47549
Code: 03 74 c0 01 10 05 03 74 b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00
RSP: 002b:00000000f55415fc EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000c018643a
RDX: 0000000020000100 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:121 [inline]
kmsan_internal_chain_origin+0xad/0x130 mm/kmsan/kmsan.c:289
__msan_chain_origin+0x57/0xa0 mm/kmsan/kmsan_instr.c:147
compat_drm_wait_vblank+0x43c/0x450 drivers/gpu/drm/drm_ioc32.c:865
drm_compat_ioctl+0x3f6/0x590 drivers/gpu/drm/drm_ioc32.c:995
__do_compat_sys_ioctl fs/ioctl.c:842 [inline]
__se_compat_sys_ioctl+0x53d/0x1100 fs/ioctl.c:793
__ia32_compat_sys_ioctl+0x4a/0x70 fs/ioctl.c:793
do_syscall_32_irqs_on arch/x86/entry/common.c:79 [inline]
__do_fast_syscall_32+0x102/0x160 arch/x86/entry/common.c:141
do_fast_syscall_32+0x6a/0xc0 arch/x86/entry/common.c:166
do_SYSENTER_32+0x73/0x90 arch/x86/entry/common.c:209
entry_SYSENTER_compat_after_hwframe+0x4d/0x5c

Local variable ----req@compat_drm_wait_vblank created at:
compat_drm_wait_vblank+0x7b/0x450 drivers/gpu/drm/drm_ioc32.c:849
compat_drm_wait_vblank+0x7b/0x450 drivers/gpu/drm/drm_ioc32.c:849

Bytes 12-15 of 16 are uninitialized
Memory access of size 16 starts at ffff88814ffe3c98
Data copied to user address 0000000020000100
=====================================================


---
This report 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 syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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