Re: [PATCH] fs: Prevent non-symlinks from entering pick link

[Al Viro]

On Wed, Jun 18, 2025 at 11:30:48AM +0800, Edward Adam Davis wrote:
> The reproducer uses a file0 on a ntfs3 file system with a corrupted i_link.
> When renaming, the file0's inode is marked as a bad inode because the file
> name cannot be deleted. However, before renaming, file0 is a directory.
> After the renaming fails, it is marked as a bad inode, which makes it a
> regular file. In any case, when opening it after creating a hard link,
> pick_link() should not be entered because it is not a symbolic link from
> beginning to end.
> 
> Add a check on the symbolic link before entering pick_link() to avoid
> triggering unknown exceptions when performing the i_link acquisition
> operation on other types of files.
> 
> Reported-by: syzbot+1aa90f0eb1fc3e77d969@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=1aa90f0eb1fc3e77d969
> Tested-by: syzbot+1aa90f0eb1fc3e77d969@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>

NAK.  This is not the first time that garbage is suggested and no,
we are not going to paper over that shite in fs/namei.c.

Not going to happen.

You ARE NOT ALLOWED to call make_bad_inode() on a live inode, period.
Never, ever to be done.

There's a lot of assertions it violates and there's no chance in
hell to plaster each with that kind of checks.

Fix NTFS.  End of story.