linux-kernel - Re: [AppArmor 40/41] AppArmor: all the rest

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Message-ID: <20070412113217.GA21911@ftp.linux.org.uk>
Date:	Thu, 12 Apr 2007 12:32:17 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	jjohansen@...e.de
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, chrisw@...s-sol.org,
	Andreas Gruenbacher <agruen@...e.de>
Subject: Re: [AppArmor 40/41] AppArmor: all the rest

On Thu, Apr 12, 2007 at 11:32:00AM +0100, Al Viro wrote:
> On Thu, Apr 12, 2007 at 02:08:49AM -0700, jjohansen@...e.de wrote:
> > +	} else if (profile1 > profile2) {
> > +		/* profile1 cannot be NULL here. */
> > +		spin_lock_irqsave(&profile1->lock, profile1->int_flags);
> > +		if (profile2)
> > +			spin_lock(&profile2->lock);
> > +
> > +	} else {
> > +		/* profile2 cannot be NULL here. */
> > +		spin_lock_irqsave(&profile2->lock, profile2->int_flags);
> > +		spin_lock(&profile1->lock);
> > +	}
> 
> Ahem...
> 
> profile2 is locked individually.  profile1 > profile2.  profile1 is not
> locked.  We try to lock both.  profile1 is locked OK, flags (with interrupts
> disabled) are stored into it.  We spin trying to lock profile2.  Eventually,
> whoever had held profile2 unlocks it, restoring the flags from profile2.
> We happily grab the spinlock and move on.  When we unlock the pair, we
> restore flags from profile1.  I.e. we are left with interrupts disabled.

Please, ignore - shouldn't have posted without coffee...  Flags would be
for different CPUs in that case, obviously.
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