linux-kernel - Re: [syzbot] [kernel?] KMSAN: kernel-infoleak in do_insn

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Message-ID: <687e8e18.a70a0220.693ce.00f4.GAE@google.com>
Date: Mon, 21 Jul 2025 11:59:36 -0700
From: syzbot <syzbot+a5e45f768aab5892da5d@...kaller.appspotmail.com>
To: abbotti@....co.uk, hsweeten@...ionengravers.com, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [kernel?] KMSAN: kernel-infoleak in do_insn_ioctl

syzbot has found a reproducer for the following issue on:

HEAD commit:    89be9a83ccf1 Linux 6.16-rc7
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=172b7722580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7753c32e11ff6a95
dashboard link: https://syzkaller.appspot.com/bug?extid=a5e45f768aab5892da5d
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13358fd4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=146fc4f0580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d81be8d18fda/disk-89be9a83.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/00dac9042245/vmlinux-89be9a83.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0d63e27252f4/bzImage-89be9a83.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a5e45f768aab5892da5d@...kaller.appspotmail.com

=====================================================
BUG: KMSAN: kernel-infoleak-after-free in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
BUG: KMSAN: kernel-infoleak-after-free in _inline_copy_to_user include/linux/uaccess.h:196 [inline]
BUG: KMSAN: kernel-infoleak-after-free 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]
 do_insn_ioctl+0x59c/0x6d0 drivers/comedi/comedi_fops.c:1661
 comedi_unlocked_ioctl+0x1432/0x1e80 drivers/comedi/comedi_fops.c:2286
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0x23c/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 created at:
 slab_free_hook mm/slub.c:2307 [inline]
 slab_free mm/slub.c:4643 [inline]
 kfree+0x252/0xec0 mm/slub.c:4842
 put_css_set_locked+0xf5c/0x1440 kernel/cgroup/cgroup.c:971
 cgroup_migrate_finish+0x1d0/0x7c0 kernel/cgroup/cgroup.c:2758
 cgroup_attach_task+0x6ec/0x970 kernel/cgroup/cgroup.c:2957
 __cgroup1_procs_write+0x4ba/0x670 kernel/cgroup/cgroup-v1.c:528
 cgroup1_procs_write+0x44/0x60 kernel/cgroup/cgroup-v1.c:541
 cgroup_file_write+0x38d/0x920 kernel/cgroup/cgroup.c:4183
 kernfs_fop_write_iter+0x545/0x9e0 fs/kernfs/file.c:334
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0xb4b/0x1580 fs/read_write.c:686
 ksys_write fs/read_write.c:738 [inline]
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x1fb/0x4d0 fs/read_write.c:746
 x64_sys_call+0x38c3/0x3db0 arch/x86/include/generated/asm/syscalls_64.h:2
 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

Bytes 4-59 of 60 are uninitialized
Memory access of size 60 starts at ffff88804acc6380
Data copied to user address 0000200000000080

CPU: 0 UID: 0 PID: 6052 Comm: syz.0.16 Not tainted 6.16.0-rc7-syzkaller #0 PREEMPT(none) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
=====================================================


---
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.