Re: [PATCH 3/3] XFRM: Drop packets when replay counter would overflow

James Morris
2007-12-20T22:29:16Z

On Thu, 20 Dec 2007, Paul Moore wrote:

> According to RFC4303, section 3.3.3 we need to drop outgoing packets which
> cause the replay counter to overflow:
>
> 3.3.3. Sequence Number Generation
>
> The sender's counter is initialized to 0 when an SA is established.
> The sender increments the sequence number (or ESN) counter for this
> SA and inserts the low-order 32 bits of the value into the Sequence
> Number field. Thus, the first packet sent using a given SA will
> contain a sequence number of 1.
>
> If anti-replay is enabled (the default), the sender checks to ensure
> that the counter has not cycled before inserting the new value in the
> Sequence Number field. In other words, the sender MUST NOT send a
> packet on an SA if doing so would cause the sequence number to cycle.
> An attempt to transmit a packet that would result in sequence number
> overflow is an auditable event. The audit log entry for this event
> SHOULD include the SPI value, current date/time, Source Address,
> Destination Address, and (in IPv6) the cleartext Flow ID.
>
> Signed-off-by: Paul Moore <paul.moore@hp.com>

Acked-by: James Morris <jmorris@namei.org>

> ---
>
> net/xfrm/xfrm_output.c | 5 ++++-
> 1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
> index eb3333b..284eeef 100644
> --- a/net/xfrm/xfrm_output.c
> +++ b/net/xfrm/xfrm_output.c
> @@ -57,8 +57,11 @@ static int xfrm_output_one(struct sk_buff *skb, int err)
>
> if (x->type->flags & XFRM_TYPE_REPLAY_PROT) {
> XFRM_SKB_CB(skb)->seq = ++x->replay.oseq;
> - if (unlikely(x->replay.oseq == 0))
> + if (unlikely(x->replay.oseq == 0)) {
> + x->replay.oseq--;
> xfrm_audit_state_replay_overflow(x, skb);
> + goto error;
> + }
> if (xfrm_aevent_is_on())
> xfrm_replay_notify(x, XFRM_REPLAY_UPDATE);
> }
>
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>

--
James Morris
<jmorris@namei.org>