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