Re: [PATCH 1/2] debugfs: prevent access to possibly dead file_operations at file open

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Dec 01, 2015 at 12:21:31AM +0100, Nicolai Stange wrote:
> Nothing prevents a dentry found by path lookup before a return of
> __debugfs_remove() to actually get opened after that return. Now, after
> the return of __debugfs_remove(), there are no guarantees whatsoever
> regarding the memory the corresponding inode's file_operations object
> had been kept in.
> 
> Since __debugfs_remove() is seldomly invoked, usually from module exit
> handlers only, the race is hard to trigger and the impact is very low.
> 
> A discussion of the problem outlined above as well as a suggested
> solution can be found in the (sub-)thread rooted at
> 
>   http://lkml.kernel.org/g/20130401203445.GA20862@ZenIV.linux.org.uk
>   ("Yet another pipe related oops.")
> 
> Basically, Greg KH suggests to introduce an intermediate fops and
> Al Viro points out that a pointer to the original ones may be stored in
> ->d_fsdata.

Nice work, thanks for doing this.  I'll review it in a week or so when
I've caught up on my huge pending patch queue...

greg k-h