[PATCH ipsec v2 7/7] xfrm: leave the sequence counter unchanged on ESN overflow

[Jérémy Jean]

When the 64-bit ESN counter overflows, xfrm_replay_overflow_offload_esn()
rejects the packet and rolls back the stored counter. It decrements
replay_esn->oseq even though only the local oseq has advanced, which
can later induce a reuse of the last sequence number and the
corresponding AES-GCM nonce. Both IPv4 and IPv6 are affected, yet,
processing about 2^64 packets under a single key is required to
trigger this bug, which is highly unlikely in regular use cases.

Leave replay_esn->oseq unchanged on overflow. Keep the decrement of
replay_esn->oseq_hi to undo its earlier increment.

Fixes: d7dbefc45cf5 ("xfrm: Add xfrm_replay_overflow functions for offloading")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jérémy Jean <Jeremy.Jean@xxxxxxxxxxxxxxxxx>
---
 net/xfrm/xfrm_replay.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/xfrm/xfrm_replay.c b/net/xfrm/xfrm_replay.c
index 9394953247ab9..01504e5b1ad41 100644
--- a/net/xfrm/xfrm_replay.c
+++ b/net/xfrm/xfrm_replay.c
@@ -721,7 +721,6 @@ static int xfrm_replay_overflow_offload_esn(struct xfrm_state *x, struct sk_buff
 				xo->seq.hi = oseq_hi;
 			}
 			if (replay_esn->oseq_hi == 0) {
-				replay_esn->oseq--;
 				replay_esn->oseq_hi--;
 				xfrm_audit_state_replay_overflow(x, skb);
 				err = -EOVERFLOW;
-- 
2.47.3