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Re: [PATCH] xfs: Correctly lock inode when removing suid and security ma

To: Jan Kara <jack@xxxxxxx>
Subject: Re: [PATCH] xfs: Correctly lock inode when removing suid and security marks
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 3 Dec 2014 08:59:47 +1100
Cc: Brian Foster <bfoster@xxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20141202204756.GA944@xxxxxxxxxxxxx>
References: <1417532489-26580-1-git-send-email-jack@xxxxxxx> <20141202163548.GB2113@xxxxxxxxxxxxxx> <20141202204756.GA944@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Dec 02, 2014 at 09:47:56PM +0100, Jan Kara wrote:
> On Tue 02-12-14 11:35:48, Brian Foster wrote:
> > On Tue, Dec 02, 2014 at 04:01:29PM +0100, Jan Kara wrote:
> > > Currently XFS calls file_remove_suid() without holding i_mutex. This is
> > > wrong because that function can end up messing with file permissions and
> > > security xattrs for which we need i_mutex held.
> > > 
> > > Fix the problem by grabbing iolock exclusively when we will need to
> > > change anything in permissions / xattrs.
> > > 
> > > Signed-off-by: Jan Kara <jack@xxxxxxx>
> > > ---
> > 
> > Hi Jan,
> > 
> > This doesn't compile... it looks like we need to include the security.h
> > header. FWIW, even then I get an undefined symbol error when compiling
> > as a module (security_inode_need_killpriv() does not appear to be
> > exported).
>   Sorry, forgot to amend the include in the commit. Regarding export of
> security_inode_need_killpriv() - right, I had security XFS compiled in so I
> didn't notice. Before I go and fix this up in the obvious way, does anyone
> have better idea how to fix this than to second guess what
> file_remove_suid() does? Maybe a VFS helper like file_needs_remove_suid()
> will be cleaner than what I did?

Helper seems like a sane idea - that way the filesystems can use
them as a matched pair if need be...

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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