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

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Date: Tue, 26 Sep 2023 11:31:29 +0200
From: Christoph Hellwig <hch@....de>
To: Christian Brauner <brauner@...nel.org>
Cc: Al Viro <viro@...iv.linux.org.uk>, Christoph Hellwig <hch@....de>,
	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 09:56:57AM +0200, Christian Brauner wrote:
> > BTW, this part of commit message in 2c18a63b760a is rather confused:
> >     Recent rework moved block device closing out of sb->put_super() and into
> >     sb->kill_sb() to avoid deadlocks as s_umount is held in put_super() and
> >     blkdev_put() can end up taking s_umount again.
> > 
> > That was *NOT* what a recent rework had done.  Block device closing had never
> > been inside ->put_super() - at no point since that (closing, that is) had been
> > introduced back in 0.97 ;-)  ->put_super() predates it (0.95c+).
> 
> I think the commit message probably just isn't clear enough. The main
> block device of a superblock isn't closed in sb->put_super(). That's
> always been closed in kill_block_super() after generic_shutdown_super().

Yes.

> But afaict filesystem like ext4 and xfs may have additional block
> devices open exclusively and closed them in sb->put_super():
> 
> xfs_fs_put_super()
> -> xfs_close_devices()
>    -> xfs_blkdev_put()
>       -> blkdev_put()
> 
> ext4_put_super()
> -> ext4_blkdev_remove()
>    -> blkdev_put()

Yes.