KMSAN: kernel-infoleak in tty_compat_ioctl

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    8bbbc5cf kmsan: don't compile memmove
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=1280ea7ee00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cd0e9a6b0e555cc3
dashboard link: https://syzkaller.appspot.com/bug?extid=8da9175e28eadcb203ce
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1722a3d9e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1071e265e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8da9175e28eadcb203ce@xxxxxxxxxxxxxxxxxxxxxxxxx

=====================================================
BUG: KMSAN: kernel-infoleak in kmsan_copy_to_user+0x81/0x90 mm/kmsan/kmsan_hooks.c:253
CPU: 1 PID: 11476 Comm: syz-executor814 Not tainted 5.6.0-rc2-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+0x1c9/0x220 lib/dump_stack.c:118
 kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:118
 kmsan_internal_check_memory+0x238/0x3d0 mm/kmsan/kmsan.c:423
 kmsan_copy_to_user+0x81/0x90 mm/kmsan/kmsan_hooks.c:253
 _copy_to_user+0x15a/0x1f0 lib/usercopy.c:33
 copy_to_user include/linux/uaccess.h:174 [inline]
 compat_tty_tiocgserial drivers/tty/tty_io.c:2748 [inline]
 tty_compat_ioctl+0x1482/0x1850 drivers/tty/tty_io.c:2846
 __do_compat_sys_ioctl fs/ioctl.c:857 [inline]
 __se_compat_sys_ioctl+0x57c/0xed0 fs/ioctl.c:808
 __ia32_compat_sys_ioctl+0xd9/0x110 fs/ioctl.c:808
 do_syscall_32_irqs_on arch/x86/entry/common.c:339 [inline]
 do_fast_syscall_32+0x3c7/0x6e0 arch/x86/entry/common.c:410
 entry_SYSENTER_compat+0x68/0x77 arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7ff7d99
Code: 90 e8 0b 00 00 00 f3 90 0f ae e8 eb f9 8d 74 26 00 89 3c 24 c3 90 90 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000ff97b20c EFLAGS: 00000213 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000000541e
RDX: 0000000020000300 RSI: 00000000080ea078 RDI: 00000000ff97b260
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Local variable ----v32.i105@tty_compat_ioctl created at:
 compat_tty_tiocgserial drivers/tty/tty_io.c:2735 [inline]
 tty_compat_ioctl+0xf12/0x1850 drivers/tty/tty_io.c:2846
 compat_tty_tiocgserial drivers/tty/tty_io.c:2735 [inline]
 tty_compat_ioctl+0xf12/0x1850 drivers/tty/tty_io.c:2846

Bytes 50-51 of 60 are uninitialized
Memory access of size 60 starts at ffffb50b0158fce0
Data copied to user address 0000000020000300
=====================================================


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