[syzbot] [tomoyo?] KMSAN: uninit-value in tomoyo_path_chown (3)

[syzbot] [tomoyo?] KMSAN: uninit-value in tomoyo_path_chown (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    2b414a95b8f7 Merge tag 's390-7.1-5' of git://git.kernel.or..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12cff156580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a0ca3b8cb3875012
dashboard link: https://syzkaller.appspot.com/bug?extid=eaae8fa60ce81f1e4eeb
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d7dcdf890eed/disk-2b414a95.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/214784598f3b/vmlinux-2b414a95.xz
kernel image: https://storage.googleapis.com/syzbot-assets/403c25c5a3db/bzImage-2b414a95.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+eaae8fa60ce81f1e4eeb@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in tomoyo_path_chown+0x128/0x270 security/tomoyo/tomoyo.c:380
 tomoyo_path_chown+0x128/0x270 security/tomoyo/tomoyo.c:380
 security_path_chown+0x1c0/0x710 security/security.c:1598
 chown_common+0x69f/0xcb0 fs/open.c:771
 do_fchownat+0x20f/0x490 fs/open.c:804
 __do_sys_chown fs/open.c:824 [inline]
 __se_sys_chown fs/open.c:822 [inline]
 __x64_sys_chown+0x9d/0x110 fs/open.c:822
 x64_sys_call+0x30cc/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:93
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15d/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable newattrs created at:
 chown_common+0xbc/0xcb0 fs/open.c:746
 do_fchownat+0x20f/0x490 fs/open.c:804

CPU: 1 UID: 0 PID: 4943 Comm: udevd Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
=====================================================


---
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Re: [syzbot] [tomoyo?] KMSAN: uninit-value in tomoyo_path_chown (3)

[Tetsuo Handa]

On 2026/06/17 17:41, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    2b414a95b8f7 Merge tag 's390-7.1-5' of git://git.kernel.or..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=12cff156580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a0ca3b8cb3875012
> dashboard link: https://syzkaller.appspot.com/bug?extid=eaae8fa60ce81f1e4eeb
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 

The AI's analysis

  In this case, `chown_common()` skips setting `newattrs.ia_vfsuid` and `newattrs.ia_vfsgid`.

at https://syzkaller.appspot.com/ai_job?id=abea5dd9-2a6e-4669-a927-d87ef7833666 is wrong.
We always set newattrs.ia_vfsuid and newattrs.ia_vfsgid before checking for -1.

  retry_deleg:
  	newattrs.ia_vfsuid = INVALID_VFSUID;
  	newattrs.ia_vfsgid = INVALID_VFSGID;
  	newattrs.ia_valid =  ATTR_CTIME;
  	if ((user != (uid_t)-1) && !setattr_vfsuid(&newattrs, uid))
  		return -EINVAL;
  	if ((group != (gid_t)-1) && !setattr_vfsgid(&newattrs, gid))
  		return -EINVAL;

Therefore, unless VFS people find something that can cause this problem,
this would be a random memory corruption which confused KMSAN.

#syz set subsystems: unclassified

#syz set no-reminders

Re: [syzbot] [tomoyo?] KMSAN: uninit-value in tomoyo_path_chown (3)

[syzbot]

> On 2026/06/17 17:41, syzbot wrote:
>> Hello,
>> 
>> syzbot found the following issue on:
>> 
>> HEAD commit:    2b414a95b8f7 Merge tag 's390-7.1-5' of git://git.kernel.or..
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=12cff156580000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=a0ca3b8cb3875012
>> dashboard link: https://syzkaller.appspot.com/bug?extid=eaae8fa60ce81f1e4eeb
>> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
>> 
>> Unfortunately, I don't have any reproducer for this issue yet.
>> 
>
> The AI's analysis
>
>   In this case, `chown_common()` skips setting `newattrs.ia_vfsuid` and `newattrs.ia_vfsgid`.
>
> at https://syzkaller.appspot.com/ai_job?id=abea5dd9-2a6e-4669-a927-d87ef7833666 is wrong.
> We always set newattrs.ia_vfsuid and newattrs.ia_vfsgid before checking for -1.
>
>   retry_deleg:
>   	newattrs.ia_vfsuid = INVALID_VFSUID;
>   	newattrs.ia_vfsgid = INVALID_VFSGID;
>   	newattrs.ia_valid =  ATTR_CTIME;
>   	if ((user != (uid_t)-1) && !setattr_vfsuid(&newattrs, uid))
>   		return -EINVAL;
>   	if ((group != (gid_t)-1) && !setattr_vfsgid(&newattrs, gid))
>   		return -EINVAL;
>
> Therefore, unless VFS people find something that can cause this problem,
> this would be a random memory corruption which confused KMSAN.
>
> #syz set subsystems: unclassified
>
> #syz set no-reminders
>

Command #1:
The specified label value is incorrect.
"unclassified" is not among the allowed values.
Please use one of the supported label values.

The following labels are suported:
actionable, missing-backport, no-reminders, prio: {low, normal, high}, subsystems: {..
see below ..}
The list of subsystems: https://syzkaller.appspot.com/upstream/subsystems?all=true