linux-kernel - Re: [PATCH] KVM: Prevent double-free on HPT resize commit path

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Message-ID: <20170228045927.GB25371@fergus.ozlabs.ibm.com>
Date:   Tue, 28 Feb 2017 15:59:27 +1100
From:   Paul Mackerras <paulus@...abs.org>
To:     David Gibson <david@...son.dropbear.id.au>
Cc:     dan.carpenter@...cle.com, linuxppc-dev@...ts.ozlabs.org,
        kvm-ppc@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: Prevent double-free on HPT resize commit path

On Tue, Feb 28, 2017 at 11:56:55AM +1100, David Gibson wrote:
> On Wed, Feb 15, 2017 at 02:40:04PM +1100, David Gibson wrote:
> > resize_hpt_release(), called once the HPT resize of a KVM guest is
> > completed (successfully or unsuccessfully) free()s the state structure for
> > the resize.  It is currently not safe to call with a NULL pointer.
> > 
> > However, one of the error paths in kvm_vm_ioctl_resize_hpt_commit() can
> > invoke it with a NULL pointer.  This will occur if userspace improperly
> > invokes KVM_PPC_RESIZE_HPT_COMMIT without previously calling
> > KVM_PPC_RESIZE_HPT_PREPARE, or if it calls COMMIT twice without an
> > intervening PREPARE.
> > 
> > To fix this potential crash bug - and maybe others like it, make it safe
> > (and a no-op) to call resize_hpt_release() with a NULL resize pointer.
> > 
> > Found by Dan Carpenter with a static checker.
> > 
> > Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> > Signed-off-by: David Gibson <david@...son.dropbear.id.au>
> 
> Ping,
> 
> Paul have you taken this one?

Yes, thanks, it's in Linus' tree now.

Paul.