Re: [PATCH 4.3 34/71] vrf: fix double free and memory corruption on register_netdevice failure

[David Ahern]

On 12/14/15 10:45 AM, Ben Hutchings wrote:
> On Sat, 2015-12-12 at 12:05 -0800, Greg Kroah-Hartman wrote:
> > 4.3-stable review patch.  If anyone has any objections, please let me
> > know.
> >
> > ------------------
> >
> > From: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx>
> >
> > [ Upstream commit 7f109f7cc37108cba7243bc832988525b0d85909 ]
> [...]
> > --- a/drivers/net/vrf.c
> > +++ b/drivers/net/vrf.c
> > @@ -581,7 +581,6 @@ static int vrf_newlink(struct net *src_n
> >   {
> >   	struct net_vrf *vrf = netdev_priv(dev);
> >   	struct net_vrf_dev *vrf_ptr;
> > -	int err;
> >
> >   	if (!data || !data[IFLA_VRF_TABLE])
> >   		return -EINVAL;
> > @@ -590,26 +589,16 @@ static int vrf_newlink(struct net *src_n
> >
> >   	dev->priv_flags |= IFF_VRF_MASTER;
> >
> > -	err = -ENOMEM;
> >   	vrf_ptr = kmalloc(sizeof(*dev->vrf_ptr), GFP_KERNEL);
> >   	if (!vrf_ptr)
> > -		goto out_fail;
> > +		return -ENOMEM;
> >
> >   	vrf_ptr->ifindex = dev->ifindex;
> >   	vrf_ptr->tb_id = vrf->tb_id;
> >
> > -	err = register_netdevice(dev);
> > -	if (err < 0)
> > -		goto out_fail;
> > -
> >   	rcu_assign_pointer(dev->vrf_ptr, vrf_ptr);
> >
> > -	return 0;
> > -
> > -out_fail:
> > -	kfree(vrf_ptr);
> > -	free_netdev(dev);
> > -	return err;
> > +	return register_netdev(dev);
> >   }
> >
> >   static size_t vrf_nl_getsize(const struct net_device *dev)
>
> This leaks *dev->vrf_ptr if register_netdevice() fails.  (This bug does
> not exist in the mainline version, as net_device::vrf_ptr no longer
> exists there.)

Good catch. The backport just needs to drop the free_netdev call:

diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
index 488c6f50df73..374feba02565 100644
--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -608,7 +608,6 @@ static int vrf_newlink(struct net *src_net, struct 
net_device *dev,

 out_fail:
        kfree(vrf_ptr);
-       free_netdev(dev);
        return err;
 }



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