netdev - Re: [PATCH] ovs: queue_userspace_packet: bail out if nla_nest

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Date:	Wed, 03 Jul 2013 19:13:55 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	Jesse Gross <jesse@...ira.com>
CC:	netdev <netdev@...r.kernel.org>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>
Subject: Re: [PATCH] ovs: queue_userspace_packet: bail out if nla_nest_start
 returns NULL

On 07/03/2013 06:32 PM, Jesse Gross wrote:
> On Wed, Jul 3, 2013 at 1:49 AM, Daniel Borkmann <dborkman@...hat.com> wrote:
>> The return value of nla_nest_start() is not checked, and can be NULL,
>> which is then being dereferenced in nla_nest_end(). Add a check to
>> prevent such situations.
>>
>> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
>> ---
>>   On top of "net-next" tree.
>>
>>   net/openvswitch/datapath.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
>> index d12d6b8..51a3c66 100644
>> --- a/net/openvswitch/datapath.c
>> +++ b/net/openvswitch/datapath.c
>> @@ -427,6 +427,10 @@ static int queue_userspace_packet(struct net *net, int dp_ifindex,
>>          upcall->dp_ifindex = dp_ifindex;
>>
>>          nla = nla_nest_start(user_skb, OVS_PACKET_ATTR_KEY);
>> +       if (unlikely(!nla)) {
>> +               err = -ENOMEM;
>> +               goto out;
>> +       }
>
> nla_nest_start() doesn't allocate any memory, it only fails if there
> isn't enough space, so the correct error code would be -EMSGSIZE.
> However, we just calculated the correct size a few lines earlier and
> we don't double check the size anywhere else, so this doesn't make a
> lot of sense to me.

Fair enough, please drop this then.
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