[PATCH net] macsec: reject replays after non-XPN receive PN exhaustion

[Sung Byeongchan <tjdqudcks0424@naver.com>]

When a non-XPN RXSA accepts PN U32_MAX, advancing the receive PN cannot
represent the next value. The replay checks subsequently accept the same
authenticated terminal frame again.

Record receive-SA exhaustion after accepting the legitimate terminal frame
and reject subsequent frames until userspace explicitly resets the PN. Keep
XPN behavior unchanged. Preserve the exhaustion state if a hardware-offload
PN update fails and the old PN is restored.

The identical terminal-PN frame crossed the controlled port twice in all
three baseline runs. All three fixed runs rejected the replay. PN max-1,
fresh terminal-frame, and bad-ICV controls retained their expected
behavior.

The demonstrated impact is a replay and integrity-policy bypass. No memory
corruption or RCE/LPE primitive was observed.

This change was prepared with assistance from OpenAI Codex. I reviewed the
source change, test results, and this commit message.

Fixes: c09440f7dcb3 ("macsec: introduce IEEE 802.1AE driver")
Assisted-by: OpenAI Codex
Signed-off-by: Sung Byeongchan <tjdqudcks0424@naver.com>
---
 drivers/net/macsec.c | 18 ++++++++++++++----
 include/net/macsec.h |  1 +
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index 78a19b1346321..906108e10b32d 100644
--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c
@@ -750,8 +750,10 @@ static bool macsec_post_decrypt(struct sk_buff *skb, struct macsec_secy *secy, u
 	/* Now perform replay protection check again
 	 * (see IEEE 802.1AE-2006 figure 10-5)
 	 */
-	if (secy->replay_protect && pn < lowest_pn &&
-	    (!secy->xpn || pn_same_half(pn, lowest_pn))) {
+	if (secy->replay_protect &&
+	    (rx_sa->exhausted ||
+	     (pn < lowest_pn &&
+	      (!secy->xpn || pn_same_half(pn, lowest_pn))))) {
 		spin_unlock(&rx_sa->lock);
 		u64_stats_update_begin(&rxsc_stats->syncp);
 		rxsc_stats->stats.InPktsLate++;
@@ -813,6 +815,8 @@ static bool macsec_post_decrypt(struct sk_buff *skb, struct macsec_secy *secy, u
 			rx_sa->next_pn_halves.upper++;
 			rx_sa->next_pn_halves.lower = pn + 1;
 		}
+		if (secy->replay_protect && !secy->xpn && pn == U32_MAX)
+			rx_sa->exhausted = true;
 
 		spin_unlock(&rx_sa->lock);
 	}
@@ -1252,8 +1256,9 @@ static rx_handler_result_t macsec_handle_frame(struct sk_buff **pskb)
 		bool late;
 
 		spin_lock(&rx_sa->lock);
-		late = rx_sa->next_pn_halves.lower >= secy->replay_window &&
-		       hdr_pn < (rx_sa->next_pn_halves.lower - secy->replay_window);
+		late = rx_sa->exhausted ||
+		       (rx_sa->next_pn_halves.lower >= secy->replay_window &&
+			hdr_pn < (rx_sa->next_pn_halves.lower - secy->replay_window));
 
 		if (secy->xpn)
 			late = late && pn_same_half(rx_sa->next_pn_halves.lower, hdr_pn);
@@ -1409,6 +1414,7 @@ static int init_rx_sa(struct macsec_rx_sa *rx_sa, char *sak, int key_len,
 
 	rx_sa->ssci = MACSEC_UNDEF_SSCI;
 	rx_sa->active = false;
+	rx_sa->exhausted = false;
 	rx_sa->next_pn = 1;
 	refcount_set(&rx_sa->refcnt, 1);
 	spin_lock_init(&rx_sa->lock);
@@ -2388,6 +2394,7 @@ static int macsec_upd_rxsa(struct sk_buff *skb, struct genl_info *info)
 	struct nlattr *tb_rxsc[MACSEC_RXSC_ATTR_MAX + 1];
 	struct nlattr *tb_sa[MACSEC_SA_ATTR_MAX + 1];
 	bool was_active;
+	bool was_exhausted;
 	pn_t prev_pn;
 	int ret = 0;
 
@@ -2426,7 +2433,9 @@ static int macsec_upd_rxsa(struct sk_buff *skb, struct genl_info *info)
 
 		spin_lock_bh(&rx_sa->lock);
 		prev_pn = rx_sa->next_pn_halves;
+		was_exhausted = rx_sa->exhausted;
 		rx_sa->next_pn = nla_get_uint(tb_sa[MACSEC_SA_ATTR_PN]);
+		rx_sa->exhausted = false;
 		spin_unlock_bh(&rx_sa->lock);
 	}
 
@@ -2462,6 +2471,7 @@ static int macsec_upd_rxsa(struct sk_buff *skb, struct genl_info *info)
 	if (tb_sa[MACSEC_SA_ATTR_PN]) {
 		spin_lock_bh(&rx_sa->lock);
 		rx_sa->next_pn_halves = prev_pn;
+		rx_sa->exhausted = was_exhausted;
 		spin_unlock_bh(&rx_sa->lock);
 	}
 	rx_sa->active = was_active;
diff --git a/include/net/macsec.h b/include/net/macsec.h
index d962093ee9237..57e9789ac75ef 100644
--- a/include/net/macsec.h
+++ b/include/net/macsec.h
@@ -136,6 +136,7 @@ struct macsec_rx_sa {
 	};
 	refcount_t refcnt;
 	bool active;
+	bool exhausted;
 	struct macsec_rx_sa_stats __percpu *stats;
 	struct macsec_rx_sc *sc;
 	struct rcu_work destroy_work;
-- 
2.43.0