[PATCH linux dev-6.12 04/14] net: mctp: separate cb from direct-addressing routing

[Marc Olberding]

From: Jeremy Kerr <jk at codeconstruct.com.au>

Now that we have the dst->haddr populated by sendmsg (when extended
addressing is in use), we no longer need to stash the link-layer address
in the skb->cb.

Instead, only use skb->cb for incoming lladdr data.

While we're at it: remove cb->src, as was never used.

Signed-off-by: Jeremy Kerr <jk at codeconstruct.com.au>
Link: https://patch.msgid.link/20250702-dev-forwarding-v5-4-1468191da8a4@codeconstruct.com.au
Signed-off-by: Paolo Abeni <pabeni at redhat.com>

(cherry picked from commit 3007f90ec0385304ab5794e9585427b73f40e32f)
---
 include/net/mctp.h |  4 ++--
 net/mctp/route.c   | 21 +++++----------------
 2 files changed, 7 insertions(+), 18 deletions(-)

diff --git a/include/net/mctp.h b/include/net/mctp.h
index 5bae4664b4dcec3915bb8d032122c8a3819da2a5..5dccf0ab751a12d14c534af8ab8eaa6b495d9f24 100644
--- a/include/net/mctp.h
+++ b/include/net/mctp.h
@@ -183,8 +183,8 @@ struct mctp_sk_key {
 struct mctp_skb_cb {
 	unsigned int	magic;
 	unsigned int	net;
-	int		ifindex; /* extended/direct addressing if set */
-	mctp_eid_t	src;
+	/* fields below provide extended addressing for ingress to recvmsg() */
+	int		ifindex;
 	unsigned char	halen;
 	unsigned char	haddr[MAX_ADDR_LEN];
 };
diff --git a/net/mctp/route.c b/net/mctp/route.c
index 3985388a6035377c04c4e4f183c4fceca8111917..23f339b4364316817b90b4fb2952c9eac445dd24 100644
--- a/net/mctp/route.c
+++ b/net/mctp/route.c
@@ -561,35 +561,28 @@ static int mctp_dst_input(struct mctp_dst *dst, struct sk_buff *skb)
 
 static int mctp_dst_output(struct mctp_dst *dst, struct sk_buff *skb)
 {
-	struct mctp_skb_cb *cb = mctp_cb(skb);
 	struct mctp_hdr *hdr = mctp_hdr(skb);
 	char daddr_buf[MAX_ADDR_LEN];
 	char *daddr = NULL;
 	int rc;
 
 	skb->protocol = htons(ETH_P_MCTP);
+	skb->pkt_type = PACKET_OUTGOING;
 
 	if (skb->len > dst->mtu) {
 		kfree_skb(skb);
 		return -EMSGSIZE;
 	}
 
-	/* If we're forwarding, we don't want to use the input path's cb,
-	 * as it holds the *source* hardware addressing information.
-	 *
-	 * We will have a PACKET_HOST skb from the dev, or PACKET_OUTGOING
-	 * from a socket; only use cb in the latter case.
-	 */
-	if (skb->pkt_type == PACKET_OUTGOING && cb->ifindex) {
-		/* direct route; use the hwaddr we stashed in sendmsg */
-		if (cb->halen != skb->dev->addr_len) {
+	/* direct route; use the hwaddr we stashed in sendmsg */
+	if (dst->halen) {
+		if (dst->halen != skb->dev->addr_len) {
 			/* sanity check, sendmsg should have already caught this */
 			kfree_skb(skb);
 			return -EMSGSIZE;
 		}
-		daddr = cb->haddr;
+		daddr = dst->haddr;
 	} else {
-		skb->pkt_type = PACKET_OUTGOING;
 		/* If lookup fails let the device handle daddr==NULL */
 		if (mctp_neigh_lookup(dst->dev, hdr->dest, daddr_buf) == 0)
 			daddr = daddr_buf;
@@ -1009,7 +1002,6 @@ int mctp_local_output(struct sock *sk, struct mctp_dst *dst,
 		      struct sk_buff *skb, mctp_eid_t daddr, u8 req_tag)
 {
 	struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk);
-	struct mctp_skb_cb *cb = mctp_cb(skb);
 	struct mctp_sk_key *key;
 	struct mctp_hdr *hdr;
 	unsigned long flags;
@@ -1064,9 +1056,6 @@ int mctp_local_output(struct sock *sk, struct mctp_dst *dst,
 	skb_reset_network_header(skb);
 	skb->dev = dst->dev->dev;
 
-	/* cb->net will have been set on initial ingress */
-	cb->src = saddr;
-
 	/* set up common header fields */
 	hdr = mctp_hdr(skb);
 	hdr->ver = 1;

-- 
2.34.1