linux-kernel - Re: [PATCH 03/11] VFS: Add security label support to *notify

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Message-ID: <20080228213932.GH32351@josefsipek.net>
Date:	Thu, 28 Feb 2008 16:39:32 -0500
From:	"Josef 'Jeff' Sipek" <jeffpc@...efsipek.net>
To:	Dave Quigley <dpquigl@...ho.nsa.gov>
Cc:	hch@...radead.org, viro@....linux.org.uk,
	trond.myklebust@....uio.no, bfields@...ldses.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 03/11] VFS: Add security label support to *notify

On Thu, Feb 28, 2008 at 04:05:11PM -0500, Dave Quigley wrote:
> 
> On Thu, 2008-02-28 at 16:15 -0500, Josef 'Jeff' Sipek wrote:
> > On Thu, Feb 28, 2008 at 03:39:30PM -0500, Dave Quigley wrote:
> > ...
> > > > Alright...so, few things...
> > > > 
> > > > 1) why do you need the locked/unlocked versions?
> > > > 
> > > > 2) instead of passing a flag to a common function, why not have:
> > > > 
> > > > vfs_setxattr_locked(....)
> > > > {
> > > > 	// original code minus the lock/unlock calls
> > > > }
> > > > 
> > > > vfs_setxattr(....)
> > > > {
> > > > 	mutex_lock(...);
> > > > 	vfs_setxattr_locked(...);
> > > > 	mutex_unlock(...);
> > > > }
> > > 
> > > What we do and what you propose aren't logically equivalent. There is a
> > > permission check inside vfs_setxattr before the mutex lock.
> > 
> > Ah, right. I didn't notice the @@ line...
> > 
> > Josef 'Jeff' Sipek.
> > 
> 
> I'm compiling a test kernel with your proposed change to make sure it
> doesn't deadlock. If it works then I'll go with your solution since its
> less messy.

I glanced at the call chain, and this one is making me uneasy:

vfs_setxattr => xattr_permission => permission => inode_op->permission

But Documentation/filesystems/Locking says that the inode permission op
doesn't need an i_mutex, so things should be ok.

Josef 'Jeff' Sipek.

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