[PATCH v2 net-next] ixgbe: Avoid unaligned access in ixgbe_atr() for LLC packets

[PATCH v2 net-next] ixgbe: Avoid unaligned access in ixgbe_atr() for LLC packets

[Sowmini Varadhan]

For LLC based protocols like lldp, stp etc., the ethernet header
is an 802.3 header with a h_proto that is not 0x800, 0x86dd, or
even 0x806.  In this world, the skb_network_header() points at
the DSAP/SSAP/..  and is not likely to be NET_IP_ALIGNed in
ixgbe_atr().

With LLC, drivers are not likely to correctly find IPVERSION,
or "6", at hdr.ipv4->version, but will instead just needlessly
trigger an unaligned access. (IPv4/IPv6 over LLC is almost never
implemented).

The unaligned access is thus avoidable: bail out quickly after
examining first->protocol.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
---
v2: Alexander Duyck comments.

 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 4d6223d..b25e603 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -7574,6 +7574,11 @@ static void ixgbe_atr(struct ixgbe_ring *ring,
 	if (!ring->atr_sample_rate)
 		return;
 
+	if (first->protocol != htons(ETH_P_IP) &&
+	    first->protocol != htons(ETH_P_IPV6) &&
+	    first->protocol != htons(ETH_P_ARP))
+		return;
+
 	ring->atr_count++;
 
 	/* snag network header to get L4 type and address */
-- 
1.7.1

Re: [PATCH v2 net-next] ixgbe: Avoid unaligned access in ixgbe_atr() for LLC packets

[Alexander Duyck]

On Mon, Mar 14, 2016 at 10:46 AM, Sowmini Varadhan
<sowmini.varadhan@oracle.com> wrote:
>
> For LLC based protocols like lldp, stp etc., the ethernet header
> is an 802.3 header with a h_proto that is not 0x800, 0x86dd, or
> even 0x806.  In this world, the skb_network_header() points at
> the DSAP/SSAP/..  and is not likely to be NET_IP_ALIGNed in
> ixgbe_atr().
>
> With LLC, drivers are not likely to correctly find IPVERSION,
> or "6", at hdr.ipv4->version, but will instead just needlessly
> trigger an unaligned access. (IPv4/IPv6 over LLC is almost never
> implemented).
>
> The unaligned access is thus avoidable: bail out quickly after
> examining first->protocol.
>
> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
> ---
> v2: Alexander Duyck comments.
>
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index 4d6223d..b25e603 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -7574,6 +7574,11 @@ static void ixgbe_atr(struct ixgbe_ring *ring,
>         if (!ring->atr_sample_rate)
>                 return;
>
> +       if (first->protocol != htons(ETH_P_IP) &&
> +           first->protocol != htons(ETH_P_IPV6) &&
> +           first->protocol != htons(ETH_P_ARP))
> +               return;
> +

One other thing I forgot to mention is that we don't support ARP so
that check could be dropped.  The ATR code only supports IPv4 or IPv6
with TCP.

- Alex

Re: [PATCH v2 net-next] ixgbe: Avoid unaligned access in ixgbe_atr() for LLC packets

[Sowmini Varadhan]

On (03/14/16 10:55), Alexander Duyck wrote:
> 
> One other thing I forgot to mention is that we don't support ARP so
> that check could be dropped.  The ATR code only supports IPv4 or IPv6
> with TCP.

I did notice that, but I left it in place because (a) it comes down
the stack with the NET_IP_ALIGNment and (b) ARP is only sent over
Ethernet II (there is no LLC SAP for ARP, which is a big reason
why ipv4 is not sent over llc, despite rfc 1042).

I figured it would not hurt to pass it down, in case we decide
to do something clever with it in the future.

--Sowmini

Re: [PATCH v2 net-next] ixgbe: Avoid unaligned access in ixgbe_atr() for LLC packets

[Alexander Duyck]

On Mon, Mar 14, 2016 at 10:59 AM, Sowmini Varadhan
<sowmini.varadhan@oracle.com> wrote:
> On (03/14/16 10:55), Alexander Duyck wrote:
>>
>> One other thing I forgot to mention is that we don't support ARP so
>> that check could be dropped.  The ATR code only supports IPv4 or IPv6
>> with TCP.
>
> I did notice that, but I left it in place because (a) it comes down
> the stack with the NET_IP_ALIGNment and (b) ARP is only sent over
> Ethernet II (there is no LLC SAP for ARP, which is a big reason
> why ipv4 is not sent over llc, despite rfc 1042).
>
> I figured it would not hurt to pass it down, in case we decide
> to do something clever with it in the future.

I figure it is better to just drop it since we don't need to be trying
to parse ARP packets anyway.

- Alex

Re: [PATCH v2 net-next] ixgbe: Avoid unaligned access in ixgbe_atr() for LLC packets

[Sowmini Varadhan]

On (03/14/16 12:20), Alexander Duyck wrote:
> I figure it is better to just drop it since we don't need to be trying
> to parse ARP packets anyway.

Ok, let me send out v3.