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Date:   Thu, 14 Sep 2023 00:27:12 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Christian Brauner <brauner@kernel.org>,
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Subject: Re: [PATCH 03/19] fs: release anon dev_t in deactivate_locked_super
Message-ID: <20230913232712.GC800259@ZenIV>
References: <20230913111013.77623-1-hch@lst.de>
 <20230913111013.77623-4-hch@lst.de>
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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).