[PATCH net v2] mctp i2c: handle NULL header address

[Matt Johnston <matt@codeconstruct.com.au>]

daddr can be NULL if there is no neighbour table entry present,
in that case the tx packet should be dropped.

saddr will normally be set by MCTP core, but in case it is NULL it
should be set to the device address.

Incorrect indent of the function arguments is also fixed.

Fixes: f5b8abf9fc3d ("mctp i2c: MCTP I2C binding driver")
Cc: stable@vger.kernel.org
Reported-by: Dung Cao <dung@os.amperecomputing.com>
Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
---
Changes in v2:
- Set saddr to device address if NULL, mention in commit message
- Fix patch prefix formatting
- Link to v1: https://lore.kernel.org/r/20241018-mctp-i2c-null-dest-v1-1-ba1ab52966e9@codeconstruct.com.au
---
 drivers/net/mctp/mctp-i2c.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/net/mctp/mctp-i2c.c b/drivers/net/mctp/mctp-i2c.c
index 4dc057c121f5d0fb9c9c48bf16b6933ae2f7b2ac..c909254e03c21518c17daf8b813e610558e074c1 100644
--- a/drivers/net/mctp/mctp-i2c.c
+++ b/drivers/net/mctp/mctp-i2c.c
@@ -579,7 +579,7 @@ static void mctp_i2c_flow_release(struct mctp_i2c_dev *midev)
 
 static int mctp_i2c_header_create(struct sk_buff *skb, struct net_device *dev,
 				  unsigned short type, const void *daddr,
-	   const void *saddr, unsigned int len)
+				  const void *saddr, unsigned int len)
 {
 	struct mctp_i2c_hdr *hdr;
 	struct mctp_hdr *mhdr;
@@ -588,8 +588,15 @@ static int mctp_i2c_header_create(struct sk_buff *skb, struct net_device *dev,
 	if (len > MCTP_I2C_MAXMTU)
 		return -EMSGSIZE;
 
-	lldst = *((u8 *)daddr);
-	llsrc = *((u8 *)saddr);
+	if (daddr)
+		lldst = *((u8 *)daddr);
+	else
+		return -EINVAL;
+
+	if (saddr)
+		llsrc = *((u8 *)saddr);
+	else
+		llsrc = dev->dev_addr;
 
 	skb_push(skb, sizeof(struct mctp_i2c_hdr));
 	skb_reset_mac_header(skb);

---
base-commit: cb560795c8c2ceca1d36a95f0d1b2eafc4074e37
change-id: 20241018-mctp-i2c-null-dest-a0ba271e0c48

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