Re: [PATCH 1/4] proc: fix NULL ->i_fop oops

[Christoph Hellwig <hch@infradead.org>]

On Fri, Nov 16, 2007 at 06:06:51PM +0300, Alexey Dobriyan wrote:
> proc_kill_inodes() can clear ->i_fop in the middle of vfs_readdir resulting in
> NULL dereference during "file->f_op->readdir(file, buf, filler)".
> 
> The solution is to remove proc_kill_inodes() completely:
> a) we don't have tricky modules implementing their tricky readdir hooks which
>    could keeping this revoke from hell.
> b) In a situation when module is gone but PDE still alive, standard readdir
>    will return only "." and "..", because pde->next was cleared by
>    remove_proc_entry().
> c) the race proc_kill_inode() destined to prevent is not completely fixed, just
>    race window made smaller, because vfs_readdir() is run without sb_lock held and
>    without file_list_lock held. Effectively, ->i_fop is cleared at random moment,
>    which can't fix properly anything.

Nice, getting rid of this is a very good step formwards.  Unfortunately
we have another copy of this junk in
security/selinux/selinuxfs.c:sel_remove_entries() which would need the
same treatment.