[PATCH net-next v4 06/10] ip6_gre: add drop reasons to the RX path

[Anton Danilov <littlesmilingcloud@gmail.com>]

Mirror the previous patch on the IPv6 side. So far gre_rcv() reported
the drops below as SKB_DROP_REASON_NOT_SPECIFIED, all from the same
kfree_skb_reason() call. Now it reports:

 - SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND when no tunnel matches,
 - SKB_DROP_REASON_HDR_TRUNC when a header is too short,
 - what __iptunnel_pull_header_reason() returns when the pull fails,
 - SKB_DROP_REASON_NOMEM when the metadata dst cannot be allocated.

Unlike ip_gre, gre_rcv() calls the helper before the tunnel lookup, so a
packet whose ETH_P_TEB inner Ethernet header or WCCPv2 extra word is cut
short is reported as SKB_DROP_REASON_PKT_TOO_SMALL whether a tunnel
matches or not.

Like their IPv4 counterparts, ip6gre_rcv() and ip6erspan_rcv() now
return SKB_NOT_DROPPED_YET where they returned PACKET_RCVD and a drop
reason where they returned PACKET_REJECT. That leaves PACKET_RCVD,
PACKET_REJECT and PACKET_NEXT without users, so remove them.
PACKET_REJECT has the value of SKB_CONSUMED, and a stray one in a
function that now returns a drop reason would build silently and be
traced as a consumed packet.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Anton Danilov <littlesmilingcloud@gmail.com>
---
 include/net/ip_tunnels.h |  4 ----
 net/ipv6/ip6_gre.c       | 46 +++++++++++++++++++++++-----------------
 2 files changed, 26 insertions(+), 24 deletions(-)

diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
index c68031d01c39..27a9e097996b 100644
--- a/include/net/ip_tunnels.h
+++ b/include/net/ip_tunnels.h
@@ -207,10 +207,6 @@ struct tnl_ptk_info {
 	int hdr_len;
 };
 
-#define PACKET_RCVD	0
-#define PACKET_REJECT	1
-#define PACKET_NEXT	2
-
 #define IP_TNL_HASH_BITS   7
 #define IP_TNL_HASH_SIZE   (1 << IP_TNL_HASH_BITS)
 
diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index d36949cbe9fa..ada48e23ca9d 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -451,7 +451,8 @@ 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 enum skb_drop_reason ip6gre_rcv(struct sk_buff *skb,
+				       const struct tnl_ptk_info *tpi)
 {
 	const struct ipv6hdr *ipv6h;
 	struct ip6_tnl *tunnel;
@@ -471,22 +472,22 @@ static int ip6gre_rcv(struct sk_buff *skb, const struct tnl_ptk_info *tpi)
 
 			tun_dst = ipv6_tun_rx_dst(skb, flags, tun_id, 0);
 			if (!tun_dst)
-				return PACKET_REJECT;
+				return SKB_DROP_REASON_NOMEM;
 
 			ip6_tnl_rcv(tunnel, skb, tpi, tun_dst, log_ecn_error);
 		} else {
 			ip6_tnl_rcv(tunnel, skb, tpi, NULL, log_ecn_error);
 		}
 
-		return PACKET_RCVD;
+		return SKB_NOT_DROPPED_YET;
 	}
 
-	return PACKET_REJECT;
+	return SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND;
 }
 
-static int ip6erspan_rcv(struct sk_buff *skb,
-			 struct tnl_ptk_info *tpi,
-			 int gre_hdr_len)
+static enum skb_drop_reason ip6erspan_rcv(struct sk_buff *skb,
+					  struct tnl_ptk_info *tpi,
+					  int gre_hdr_len)
 {
 	struct erspan_base_hdr *ershdr;
 	const struct ipv6hdr *ipv6h;
@@ -495,7 +496,7 @@ static int ip6erspan_rcv(struct sk_buff *skb,
 	u8 ver;
 
 	if (unlikely(!pskb_may_pull(skb, sizeof(*ershdr))))
-		return PACKET_REJECT;
+		return SKB_DROP_REASON_HDR_TRUNC;
 
 	ipv6h = ipv6_hdr(skb);
 	ershdr = (struct erspan_base_hdr *)skb->data;
@@ -506,14 +507,16 @@ static int ip6erspan_rcv(struct sk_buff *skb,
 				      tpi->proto);
 	if (tunnel) {
 		int len = erspan_hdr_len(ver);
+		enum skb_drop_reason reason;
 
 		if (unlikely(!pskb_may_pull(skb, len)))
-			return PACKET_REJECT;
+			return SKB_DROP_REASON_HDR_TRUNC;
 
-		if (__iptunnel_pull_header(skb, len,
-					   htons(ETH_P_TEB),
-					   false, false) < 0)
-			return PACKET_REJECT;
+		reason = __iptunnel_pull_header_reason(skb, len,
+						       htons(ETH_P_TEB),
+						       false, false);
+		if (reason)
+			return reason;
 
 		if (tunnel->parms.collect_md) {
 			struct erspan_metadata *pkt_md, *md;
@@ -530,7 +533,7 @@ static int ip6erspan_rcv(struct sk_buff *skb,
 			tun_dst = ipv6_tun_rx_dst(skb, flags, tun_id,
 						  sizeof(*md));
 			if (!tun_dst)
-				return PACKET_REJECT;
+				return SKB_DROP_REASON_NOMEM;
 
 			/* MUST set options_len before referencing options */
 			info = &tun_dst->u.tun_info;
@@ -558,10 +561,10 @@ static int ip6erspan_rcv(struct sk_buff *skb,
 			ip6_tnl_rcv(tunnel, skb, tpi, NULL, log_ecn_error);
 		}
 
-		return PACKET_RCVD;
+		return SKB_NOT_DROPPED_YET;
 	}
 
-	return PACKET_REJECT;
+	return SKB_DROP_REASON_GRE_TUNNEL_NOT_FOUND;
 }
 
 static int gre_rcv(struct sk_buff *skb)
@@ -572,19 +575,22 @@ static int gre_rcv(struct sk_buff *skb)
 	reason = gre_parse_header(skb, &tpi, false, htons(ETH_P_IPV6), 0);
 	if (reason)
 		goto drop;
-	reason = SKB_DROP_REASON_NOT_SPECIFIED;
 
-	if (iptunnel_pull_header(skb, tpi.hdr_len, tpi.proto, false))
+	reason = __iptunnel_pull_header_reason(skb, tpi.hdr_len, tpi.proto,
+					       false, false);
+	if (reason)
 		goto drop;
 
 	if (unlikely(tpi.proto == htons(ETH_P_ERSPAN) ||
 		     tpi.proto == htons(ETH_P_ERSPAN2))) {
-		if (ip6erspan_rcv(skb, &tpi, tpi.hdr_len) == PACKET_RCVD)
+		reason = ip6erspan_rcv(skb, &tpi, tpi.hdr_len);
+		if (!reason)
 			return 0;
 		goto out;
 	}
 
-	if (ip6gre_rcv(skb, &tpi) == PACKET_RCVD)
+	reason = ip6gre_rcv(skb, &tpi);
+	if (!reason)
 		return 0;
 
 out:
-- 
2.47.3