Re: [PATCH 03/19] fs: release anon dev_t in deactivate_locked_super

[Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>]

On Wed, Sep 13, 2023 at 08:09:57AM -0300, Christoph Hellwig wrote:
> Releasing an anon dev_t is a very common thing when freeing a
> super_block, as that's done for basically any not block based file
> system (modulo the odd mtd special case).  So instead of requiring
> a special ->kill_sb helper and a lot of boilerplate in more complicated
> file systems, just release the anon dev_t in deactivate_locked_super if
> the super_block was using one.
> 
> As the freeing is done after the main call to kill_super_notify, this
> removes the need for having two slightly different call sites for it.

Huh?  At this stage in your series freeing is still in ->kill_sb()
instances, after the calls of kill_anon_super() you've turned into
the calls of generic_shutdown_super().

You do split it off into a separate method later in the series, but
at this point you are reopening the same UAF that had been dealt with
in dc3216b14160 "super: ensure valid info".

Either move the introduction of ->free_sb() before that one, or
split it into lifting put_anon_bdev() (left here) and getting rid
of kill_anon_super() (after ->free_sb() introduction).