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

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Message-ID: <CAEP_g=84532Nh1wagsifOaBkCDk5eOUtG=RzWSv_Z+tPxzUOGg@mail.gmail.com>
Date:	Wed, 3 Jul 2013 09:32:55 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	Daniel Borkmann <dborkman@...hat.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 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.
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