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

[Al Viro]

On Wed, Jun 18, 2025 at 05:50:16AM +0100, Al Viro wrote:

> 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.

To elaborate a bit: if you look at the end of e.g. their attr_set_size(),
you'll see
out:
        if (is_bad) {
bad_inode:
		_ntfs_bad_inode(&ni->vfs_inode);
	}
	return err;
}

This is a bug.  So are similar places all over the place there.
You are not supposed to use make_bad_inode() as a general-purpose
"something went wrong, don't wanna see it anymore" tool.

And as long as it stays there, any fuzzing reports of ntfs are pretty
much worthless - any of those places (easily located by grepping for
_ntfs_bad_inode) can fuck the kernel up.  Once ntfs folks get around
to saner error recovery, it would make sense to start looking into
fuzzing that thing again.  Until then - nope.  Again, this is *NOT*
going to be papered over in a random set of places (pretty certain
to remain incomplete) in VFS.