netdev - [PATCH net] net: mctp: unconditionally set skb->dev on dst output

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Message-Id: <20251125-dev-forward-v1-1-54ecffcd0616@codeconstruct.com.au>
Date: Tue, 25 Nov 2025 14:48:54 +0800
From: Jeremy Kerr <jk@...econstruct.com.au>
To: Matt Johnston <matt@...econstruct.com.au>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org, Vince Chang <vince_chang@...eedtech.com>
Subject: [PATCH net] net: mctp: unconditionally set skb->dev on dst output

On transmit, we are currently relying on skb->dev being set by
mctp_local_output() when we first set up the skb destination fields.
However, forwarded skbs do not use the local_output path, so will retain
their incoming netdev as their ->dev on tx. This does not work when
we're forwarding between interfaces.

Set skb->dev unconditionally in the transmit path, to allow for proper
forwarding.

We keep the skb->dev initialisation in mctp_local_output(), as we use it
for fragmentation.

Fixes: 269936db5eb3 ("net: mctp: separate routing database from routing operations")
Suggested-by: Vince Chang <vince_chang@...eedtech.com>
Signed-off-by: Jeremy Kerr <jk@...econstruct.com.au>
---
 net/mctp/route.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/mctp/route.c b/net/mctp/route.c
index 4d314e062ba9c4137f196482880660be67a71b11..2ac4011a953fffe9e01f3bfe0f571b3727b3e903 100644
--- a/net/mctp/route.c
+++ b/net/mctp/route.c
@@ -623,6 +623,7 @@ static int mctp_dst_output(struct mctp_dst *dst, struct sk_buff *skb)

 	skb->protocol = htons(ETH_P_MCTP);
 	skb->pkt_type = PACKET_OUTGOING;
+	skb->dev = dst->dev->dev;

 	if (skb->len > dst->mtu) {
 		kfree_skb(skb);

---
base-commit: 4c19c4fa8dabb945a017c1910605ab2616725c6c
change-id: 20251125-dev-forward-932c006dec72

Best regards,
-- 
Jeremy Kerr <jk@...econstruct.com.au>