[syzbot] [i2c?] KMSAN: kernel-infoleak in i2cdev_ioctl_smbus

[syzbot <syzbot+08b819a87faa6def6dfb@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    02ddfb981de8 Merge tag 'scsi-fixes' of git://git.kernel.or..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=166989b3980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9dc42c34a3f5c357
dashboard link: https://syzkaller.appspot.com/bug?extid=08b819a87faa6def6dfb
compiler:       Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1593b02f980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=154d41cc580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5ca57f5a3f77/disk-02ddfb98.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3f23cbc11e68/vmlinux-02ddfb98.xz
kernel image: https://storage.googleapis.com/syzbot-assets/73e63afac354/bzImage-02ddfb98.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+08b819a87faa6def6dfb@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
BUG: KMSAN: kernel-infoleak in _inline_copy_to_user include/linux/uaccess.h:196 [inline]
BUG: KMSAN: kernel-infoleak in _copy_to_user+0xcc/0x120 lib/usercopy.c:26
 instrument_copy_to_user include/linux/instrumented.h:114 [inline]
 _inline_copy_to_user include/linux/uaccess.h:196 [inline]
 _copy_to_user+0xcc/0x120 lib/usercopy.c:26
 copy_to_user include/linux/uaccess.h:225 [inline]
 i2cdev_ioctl_smbus+0x586/0x660 drivers/i2c/i2c-dev.c:394
 i2cdev_ioctl+0xa14/0xf40 drivers/i2c/i2c-dev.c:478
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0x239/0x400 fs/ioctl.c:892
 __x64_sys_ioctl+0x97/0xe0 fs/ioctl.c:892
 x64_sys_call+0x1ebe/0x3db0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0x1b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
 i2c_smbus_xfer_emulated drivers/i2c/i2c-core-smbus.c:495 [inline]
 __i2c_smbus_xfer+0x254d/0x2f60 drivers/i2c/i2c-core-smbus.c:607
 i2c_smbus_xfer+0x31d/0x4d0 drivers/i2c/i2c-core-smbus.c:545
 i2cdev_ioctl_smbus+0x4a1/0x660 drivers/i2c/i2c-dev.c:389
 i2cdev_ioctl+0xa14/0xf40 drivers/i2c/i2c-dev.c:478
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0x239/0x400 fs/ioctl.c:892
 __x64_sys_ioctl+0x97/0xe0 fs/ioctl.c:892
 x64_sys_call+0x1ebe/0x3db0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0x1b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable msgbuf1.i created at:
 i2c_smbus_xfer_emulated drivers/i2c/i2c-core-smbus.c:334 [inline]
 __i2c_smbus_xfer+0x86a/0x2f60 drivers/i2c/i2c-core-smbus.c:607
 i2c_smbus_xfer+0x31d/0x4d0 drivers/i2c/i2c-core-smbus.c:545

Bytes 0-1 of 2 are uninitialized
Memory access of size 2 starts at ffff88812e8b7d06
Data copied to user address 0000200000000080

CPU: 1 UID: 0 PID: 5885 Comm: syz-executor221 Not tainted 6.15.0-rc3-syzkaller-00094-g02ddfb981de8 #0 PREEMPT(undef) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
=====================================================


---
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.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup