[PATCH net-next v2 5/8] ip6_gre: add drop reasons to the RX path

[Anton Danilov <littlesmilingcloud@gmail.com>]

Mirror the previous patch on the IPv6 side: report
SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND when no tunnel matches the packet,
and tell that apart from a header that cannot be pulled
(SKB_DROP_REASON_HDR_TRUNC) or a metadata allocation failure
(SKB_DROP_REASON_NOMEM), which so far all ended up in the same plain
kfree_skb() in gre_rcv().

ip6gre_rcv() and ip6erspan_rcv() get the same output parameter as their
IPv4 counterparts.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Anton Danilov <littlesmilingcloud@gmail.com>
---
 net/ipv6/ip6_gre.c | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 78854cc2dac9..047c4f57a828 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -454,7 +454,8 @@ static int ip6gre_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 	return 0;
 }
 
-static int ip6gre_rcv(struct sk_buff *skb, const struct tnl_ptk_info *tpi)
+static int ip6gre_rcv(struct sk_buff *skb, const struct tnl_ptk_info *tpi,
+		      enum skb_drop_reason *reason)
 {
 	const struct ipv6hdr *ipv6h;
 	struct ip6_tnl *tunnel;
@@ -473,8 +474,10 @@ static int ip6gre_rcv(struct sk_buff *skb, const struct tnl_ptk_info *tpi)
 			tun_id = key32_to_tunnel_id(tpi->key);
 
 			tun_dst = ipv6_tun_rx_dst(skb, flags, tun_id, 0);
-			if (!tun_dst)
+			if (!tun_dst) {
+				*reason = SKB_DROP_REASON_NOMEM;
 				return PACKET_REJECT;
+			}
 
 			ip6_tnl_rcv(tunnel, skb, tpi, tun_dst, log_ecn_error);
 		} else {
@@ -484,12 +487,14 @@ static int ip6gre_rcv(struct sk_buff *skb, const struct tnl_ptk_info *tpi)
 		return PACKET_RCVD;
 	}
 
+	*reason = SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND;
 	return PACKET_REJECT;
 }
 
 static int ip6erspan_rcv(struct sk_buff *skb,
 			 struct tnl_ptk_info *tpi,
-			 int gre_hdr_len)
+			 int gre_hdr_len,
+			 enum skb_drop_reason *reason)
 {
 	struct erspan_base_hdr *ershdr;
 	const struct ipv6hdr *ipv6h;
@@ -497,8 +502,10 @@ static int ip6erspan_rcv(struct sk_buff *skb,
 	struct ip6_tnl *tunnel;
 	u8 ver;
 
-	if (unlikely(!pskb_may_pull(skb, sizeof(*ershdr))))
+	if (unlikely(!pskb_may_pull(skb, sizeof(*ershdr)))) {
+		*reason = SKB_DROP_REASON_HDR_TRUNC;
 		return PACKET_REJECT;
+	}
 
 	ipv6h = ipv6_hdr(skb);
 	ershdr = (struct erspan_base_hdr *)skb->data;
@@ -510,13 +517,17 @@ static int ip6erspan_rcv(struct sk_buff *skb,
 	if (tunnel) {
 		int len = erspan_hdr_len(ver);
 
-		if (unlikely(!pskb_may_pull(skb, len)))
+		if (unlikely(!pskb_may_pull(skb, len))) {
+			*reason = SKB_DROP_REASON_HDR_TRUNC;
 			return PACKET_REJECT;
+		}
 
 		if (__iptunnel_pull_header(skb, len,
 					   htons(ETH_P_TEB),
-					   false, false) < 0)
+					   false, false) < 0) {
+			*reason = SKB_DROP_REASON_HDR_TRUNC;
 			return PACKET_REJECT;
+		}
 
 		if (tunnel->parms.collect_md) {
 			struct erspan_metadata *pkt_md, *md;
@@ -532,8 +543,10 @@ static int ip6erspan_rcv(struct sk_buff *skb,
 
 			tun_dst = ipv6_tun_rx_dst(skb, flags, tun_id,
 						  sizeof(*md));
-			if (!tun_dst)
+			if (!tun_dst) {
+				*reason = SKB_DROP_REASON_NOMEM;
 				return PACKET_REJECT;
+			}
 
 			/* MUST set options_len before referencing options */
 			info = &tun_dst->u.tun_info;
@@ -564,6 +577,7 @@ static int ip6erspan_rcv(struct sk_buff *skb,
 		return PACKET_RCVD;
 	}
 
+	*reason = SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND;
 	return PACKET_REJECT;
 }
 
@@ -577,17 +591,19 @@ static int gre_rcv(struct sk_buff *skb)
 	if (hdr_len < 0)
 		goto drop;
 
-	if (iptunnel_pull_header(skb, hdr_len, tpi.proto, false))
+	if (iptunnel_pull_header(skb, hdr_len, tpi.proto, false)) {
+		reason = SKB_DROP_REASON_HDR_TRUNC;
 		goto drop;
+	}
 
 	if (unlikely(tpi.proto == htons(ETH_P_ERSPAN) ||
 		     tpi.proto == htons(ETH_P_ERSPAN2))) {
-		if (ip6erspan_rcv(skb, &tpi, hdr_len) == PACKET_RCVD)
+		if (ip6erspan_rcv(skb, &tpi, hdr_len, &reason) == PACKET_RCVD)
 			return 0;
 		goto out;
 	}
 
-	if (ip6gre_rcv(skb, &tpi) == PACKET_RCVD)
+	if (ip6gre_rcv(skb, &tpi, &reason) == PACKET_RCVD)
 		return 0;
 
 out:
-- 
2.47.3