Re: [syzbot] [kernel?] KMSAN: kernel-infoleak in vmci_host_unlocked_ioctl (3)

[syzbot <syzbot+9b9124ae9b12d5af5d95@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KMSAN: kernel-infoleak in vmci_host_unlocked_ioctl

=====================================================
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]
 vmci_host_do_receive_datagram drivers/misc/vmw_vmci/vmci_host.c:439 [inline]
 vmci_host_unlocked_ioctl+0x1ead/0x5240 drivers/misc/vmw_vmci/vmci_host.c:933
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0x239/0x400 fs/ioctl.c:893
 __x64_sys_ioctl+0x97/0xe0 fs/ioctl.c:893
 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+0xd9/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
 kmemdup_noprof+0xb0/0x100 mm/util.c:139
 kmemdup_noprof include/linux/fortify-string.h:765 [inline]
 dg_dispatch_as_host drivers/misc/vmw_vmci/vmci_datagram.c:272 [inline]
 vmci_datagram_dispatch+0x4eb/0x1560 drivers/misc/vmw_vmci/vmci_datagram.c:340
 ctx_fire_notification drivers/misc/vmw_vmci/vmci_context.c:257 [inline]
 ctx_free_ctx drivers/misc/vmw_vmci/vmci_context.c:435 [inline]
 kref_put include/linux/kref.h:65 [inline]
 vmci_ctx_put+0x88e/0x15d0 drivers/misc/vmw_vmci/vmci_context.c:497
 vmci_ctx_destroy+0x15d/0x250 drivers/misc/vmw_vmci/vmci_context.c:195
 vmci_host_do_init_context drivers/misc/vmw_vmci/vmci_host.c:341 [inline]
 vmci_host_unlocked_ioctl+0x45cd/0x5240 drivers/misc/vmw_vmci/vmci_host.c:929
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0x239/0x400 fs/ioctl.c:893
 __x64_sys_ioctl+0x97/0xe0 fs/ioctl.c:893
 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+0xd9/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable ev.i.i created at:
 ctx_fire_notification drivers/misc/vmw_vmci/vmci_context.c:248 [inline]
 ctx_free_ctx drivers/misc/vmw_vmci/vmci_context.c:435 [inline]
 kref_put include/linux/kref.h:65 [inline]
 vmci_ctx_put+0x76b/0x15d0 drivers/misc/vmw_vmci/vmci_context.c:497
 vmci_ctx_destroy+0x15d/0x250 drivers/misc/vmw_vmci/vmci_context.c:195

Byte 31 of 40 is uninitialized
Memory access of size 40 starts at ffff8880219a0880
Data copied to user address 000000000000a4bf

CPU: 0 UID: 0 PID: 6814 Comm: syz.0.16 Not tainted 6.16.0-rc2-syzkaller-00318-g739a6c93cc75-dirty #0 PREEMPT(undef) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
=====================================================


Tested on:

commit:         739a6c93 Merge tag 'nfsd-6.16-1' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12580ebc580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=db26f33438d76de9
dashboard link: https://syzkaller.appspot.com/bug?extid=9b9124ae9b12d5af5d95
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16fdf30c580000