linux-kernel - Re: [PATCH 4.4 017/268] do d_instantiate/unlock_new

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Date:   Fri, 08 Jun 2018 14:17:49 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     stable@...r.kernel.org, Mike Marshall <hubcap@...ibond.com>,
        Andreas Dilger <adilger@...ger.ca>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4.4 017/268] do d_instantiate/unlock_new_inode
 combinations safely

On Mon, 2018-05-28 at 11:59 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Al Viro <viro@...iv.linux.org.uk>
> 
> commit 1e2e547a93a00ebc21582c06ca3c6cfea2a309ee upstream.
> 
> For anything NFS-exported we do _not_ want to unlock new inode
> before it has grown an alias; original set of fixes got the
> ordering right, but missed the nasty complication in case of
> lockdep being enabled - unlock_new_inode() does
> 	lockdep_annotate_inode_mutex_key(inode)
> which can only be done before anyone gets a chance to touch
> ->i_mutex.  Unfortunately, flipping the order and doing
> unlock_new_inode() before d_instantiate() opens a window when
> mkdir can race with open-by-fhandle on a guessed fhandle, leading
> to multiple aliases for a directory inode and all the breakage
> that follows from that.
> 
> 	Correct solution: a new primitive (d_instantiate_new())
> combining these two in the right order - lockdep annotate, then
> d_instantiate(), then the rest of unlock_new_inode().  All
> combinations of d_instantiate() with unlock_new_inode() should
> be converted to that.
[...]

I think you missed xfs, which has a wrapper around unlock_new_inode()
called xfs_finish_inode_setup().  It looks like xfs_generic_create()
and xfs_vn_symlink() still need this conversion.

Ben.

-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom