linux-kernel - Re: [PATCH 4.3 34/71] vrf: fix double free and memory corruption on register

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Date:	Mon, 14 Dec 2015 11:59:15 -0700
From:	David Ahern <dsa@...ulusnetworks.com>
To:	Ben Hutchings <ben@...adent.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Cc:	stable@...r.kernel.org,
	Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 4.3 34/71] vrf: fix double free and memory corruption on
 register_netdevice failure

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@...ulusnetworks.com>
>>
>> [ 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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