netdev - [PATCH net] net: mctp i3c: Copy headers if cloned

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Message-Id: <20250306-matt-i3c-cow-head-v1-1-d5e6a5495227@codeconstruct.com.au>
Date: Thu, 06 Mar 2025 18:24:18 +0800
From: Matt Johnston <matt@...econstruct.com.au>
To: Jeremy Kerr <jk@...econstruct.com.au>, 
 Andrew Lunn <andrew+netdev@...n.ch>, 
 "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, Matt Johnston <matt@...econstruct.com.au>
Subject: [PATCH net] net: mctp i3c: Copy headers if cloned

Use skb_cow_head() prior to modifying the tx skb. This is necessary
when the skb has been cloned, to avoid modifying other shared clones.

Signed-off-by: Matt Johnston <matt@...econstruct.com.au>
Fixes: c8755b29b58e ("mctp i3c: MCTP I3C driver")
---
 drivers/net/mctp/mctp-i3c.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/mctp/mctp-i3c.c b/drivers/net/mctp/mctp-i3c.c
index c1e72253063b54a9c2ff9e45e6202347b8c962a7..c678f79aa35611272a4a410c14dcaeea290d265c 100644
--- a/drivers/net/mctp/mctp-i3c.c
+++ b/drivers/net/mctp/mctp-i3c.c
@@ -506,10 +506,15 @@ static int mctp_i3c_header_create(struct sk_buff *skb, struct net_device *dev,
 	   const void *saddr, unsigned int len)
 {
 	struct mctp_i3c_internal_hdr *ihdr;
+	int rc;

 	if (!daddr || !saddr)
 		return -EINVAL;

+	rc = skb_cow_head(skb, sizeof(struct mctp_i3c_internal_hdr));
+	if (rc)
+		return rc;
+
 	skb_push(skb, sizeof(struct mctp_i3c_internal_hdr));
 	skb_reset_mac_header(skb);
 	ihdr = (void *)skb_mac_header(skb);

---
base-commit: 0e7633d7b95b67f1758aea19f8e85621c5f506a3
change-id: 20250306-matt-i3c-cow-head-6a3df8aedf7e

Best regards,
-- 
Matt Johnston <matt@...econstruct.com.au>