Re: [Question] Unlinking original file of bind mounted file.

[Yun Levi <ppbuk5246@gmail.com>]

> No, it doesn't change the refcount of the dentry.  The unlink does temporarily
> increment, and then decrement, the refcount.  However, there is still another
> reference that's held by the bind mount.  For that reason, the dentry's inode is
> not released yet; instead, the dentry is just made unavailable to lookups.
>

>You can't actually do that, because the unlink fails with EBUSY.  And even if
> you could, it would be a different dentry (b instead of a).

Thanks for the correction!. I've said wrong sorry!


> If you have a reproducer for an actual crash, please provide it.  (And if you do
> indeed have an actual crash, please consider that its root cause may be
> completely unrelated to the theory that you've described...)

What I describe doesn't cause any panic. but I've traced with crash in
live below situation.:

======================================================
/**
 * NOT directory bind, file bind.
 */
1. mount --bind {original file} {bind file}

  // original's inode->i_count = 1, inode->i_nlink =0, and ext4_inode
becomes orphaned,
  // inode->i_no which managed by ext4 is freed and become reusable.
2. rm -f {original file}
=======================================================

It's not issued remove of bind itself. after step (2)
In the view of VFS, inode seems live, but in the view of EXT4, it
becomes "orphaned" and
its inode->i_no which managed by ext4. was removed and reuse by other
created file.

In that situation, if inode->i_no is reused, via bind fil,
It seems "arbitrary access" the data of new created one with same i_no.
(write, and read...)

What I wonder is that it's intended action or not.
IMHO, should it prohibit to unlink of original to prevent above
arbitrary access?

Thanks.

--
Sincerely,
Levi