netdev - [PATCH] net: mctp i2c: Copy headers if cloned

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Message-Id: <20250306-matt-mctp-i2c-cow-v1-1-293827212681@codeconstruct.com.au>
Date: Thu, 06 Mar 2025 10:33:20 +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>, 
 Wolfram Sang <wsa@...nel.org>
Cc: netdev@...r.kernel.org, Matt Johnston <matt@...econstruct.com.au>
Subject: [PATCH] net: mctp i2c: 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: f5b8abf9fc3d ("mctp i2c: MCTP I2C binding driver")
---
 drivers/net/mctp/mctp-i2c.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/mctp/mctp-i2c.c b/drivers/net/mctp/mctp-i2c.c
index e3dcdeacc12c590c0790c9425eb2d997937c1bb9..d74d47dd6e04dcf4163bb8cdc446dc3c649880d2 100644
--- a/drivers/net/mctp/mctp-i2c.c
+++ b/drivers/net/mctp/mctp-i2c.c
@@ -583,6 +583,7 @@ static int mctp_i2c_header_create(struct sk_buff *skb, struct net_device *dev,
 	struct mctp_i2c_hdr *hdr;
 	struct mctp_hdr *mhdr;
 	u8 lldst, llsrc;
+	int rc;

 	if (len > MCTP_I2C_MAXMTU)
 		return -EMSGSIZE;
@@ -593,6 +594,10 @@ static int mctp_i2c_header_create(struct sk_buff *skb, struct net_device *dev,
 	lldst = *((u8 *)daddr);
 	llsrc = *((u8 *)saddr);

+	rc = skb_cow_head(skb, sizeof(struct mctp_i2c_hdr));
+	if (rc)
+		return rc;
+
 	skb_push(skb, sizeof(struct mctp_i2c_hdr));
 	skb_reset_mac_header(skb);
 	hdr = (void *)skb_mac_header(skb);

---
base-commit: 3c9231ea6497dfc50ac0ef69fff484da27d0df66
change-id: 20250306-matt-mctp-i2c-cow-e9f028942734

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