[PATCH net-next v2] xfrm: introduce oseq-may-wrap flag

["Petr Vaněk" <pv@excello.cz>]

RFC 4303 in section 3.3.3 suggests to disable anti-replay for manually
distributed ICVs in which case the sender does not need to monitor or
reset the counter. However, the sender still increments the counter and
when it reaches the maximum value, the counter rolls over back to zero.

This patch introduces new extra_flag XFRM_SA_XFLAG_OSEQ_MAY_WRAP which
allows sequence number to cycle in outbound packets if set. This flag is
used only in legacy and bmp code, because esn should not be negotiated
if anti-replay is disabled (see note in 3.3.3 section).

Signed-off-by: Petr Vaněk <pv@excello.cz>
---
 include/uapi/linux/xfrm.h |  1 +
 net/xfrm/xfrm_replay.c    | 12 ++++++++----
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/xfrm.h b/include/uapi/linux/xfrm.h
index 5f3b9fec7b5f..b701244334b5 100644
--- a/include/uapi/linux/xfrm.h
+++ b/include/uapi/linux/xfrm.h
@@ -387,6 +387,7 @@ struct xfrm_usersa_info {
 };
 
 #define XFRM_SA_XFLAG_DONT_ENCAP_DSCP	1
+#define XFRM_SA_XFLAG_OSEQ_MAY_WRAP	2
 
 struct xfrm_usersa_id {
 	xfrm_address_t			daddr;
diff --git a/net/xfrm/xfrm_replay.c b/net/xfrm/xfrm_replay.c
index 98943f8d01aa..c6a4338a0d08 100644
--- a/net/xfrm/xfrm_replay.c
+++ b/net/xfrm/xfrm_replay.c
@@ -89,7 +89,8 @@ static int xfrm_replay_overflow(struct xfrm_state *x, struct sk_buff *skb)
 	if (x->type->flags & XFRM_TYPE_REPLAY_PROT) {
 		XFRM_SKB_CB(skb)->seq.output.low = ++x->replay.oseq;
 		XFRM_SKB_CB(skb)->seq.output.hi = 0;
-		if (unlikely(x->replay.oseq == 0)) {
+		if (unlikely(x->replay.oseq == 0) &&
+		    !(x->props.extra_flags & XFRM_SA_XFLAG_OSEQ_MAY_WRAP)) {
 			x->replay.oseq--;
 			xfrm_audit_state_replay_overflow(x, skb);
 			err = -EOVERFLOW;
@@ -168,7 +169,8 @@ static int xfrm_replay_overflow_bmp(struct xfrm_state *x, struct sk_buff *skb)
 	if (x->type->flags & XFRM_TYPE_REPLAY_PROT) {
 		XFRM_SKB_CB(skb)->seq.output.low = ++replay_esn->oseq;
 		XFRM_SKB_CB(skb)->seq.output.hi = 0;
-		if (unlikely(replay_esn->oseq == 0)) {
+		if (unlikely(replay_esn->oseq == 0) &&
+		    !(x->props.extra_flags & XFRM_SA_XFLAG_OSEQ_MAY_WRAP)) {
 			replay_esn->oseq--;
 			xfrm_audit_state_replay_overflow(x, skb);
 			err = -EOVERFLOW;
@@ -572,7 +574,8 @@ static int xfrm_replay_overflow_offload(struct xfrm_state *x, struct sk_buff *sk
 
 		XFRM_SKB_CB(skb)->seq.output.hi = 0;
 		xo->seq.hi = 0;
-		if (unlikely(oseq < x->replay.oseq)) {
+		if (unlikely(oseq < x->replay.oseq) &&
+		    !(x->props.extra_flags & XFRM_SA_XFLAG_OSEQ_MAY_WRAP)) {
 			xfrm_audit_state_replay_overflow(x, skb);
 			err = -EOVERFLOW;
 
@@ -611,7 +614,8 @@ static int xfrm_replay_overflow_offload_bmp(struct xfrm_state *x, struct sk_buff
 
 		XFRM_SKB_CB(skb)->seq.output.hi = 0;
 		xo->seq.hi = 0;
-		if (unlikely(oseq < replay_esn->oseq)) {
+		if (unlikely(oseq < replay_esn->oseq) &&
+		    !(x->props.extra_flags & XFRM_SA_XFLAG_OSEQ_MAY_WRAP)) {
 			xfrm_audit_state_replay_overflow(x, skb);
 			err = -EOVERFLOW;
 
-- 
2.26.2