linux-hardening - Re: [PATCH 03/19] fs: release anon dev_t in deactivate_locked

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Message-ID: <20230914023705.GH800259@ZenIV>
Date:   Thu, 14 Sep 2023 03:37:05 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Christoph Hellwig <hch@....de>
Cc:     Christian Brauner <brauner@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Tejun Heo <tj@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Damien Le Moal <dlemoal@...nel.org>,
        Naohiro Aota <naohiro.aota@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-hardening@...r.kernel.org,
        cgroups@...r.kernel.org
Subject: Re: [PATCH 03/19] fs: release anon dev_t in deactivate_locked_super

On Thu, Sep 14, 2023 at 12:27:12AM +0100, Al Viro wrote:
> 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).

Actually, looking at the final stage in the series, you still have
kill_super_notify() done *AFTER* ->free_sb() call.  So the problem
persists until the very end...