[PATCH net v3] 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 usually be set by MCTP core, but check for NULL in case a
packet is transmitted by a different protocol.

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 v3:
- Revert to simpler saddr check of v1, mention in commit message
- Revert whitespace change from v2
- Link to v2: https://lore.kernel.org/r/20241021-mctp-i2c-null-dest-v2-1-4503e478517c@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 | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/mctp/mctp-i2c.c b/drivers/net/mctp/mctp-i2c.c
index 4dc057c121f5d0fb9c9c48bf16b6933ae2f7b2ac..e70fb66879941f3937b7ffc5bc1e20a8a435a441 100644
--- a/drivers/net/mctp/mctp-i2c.c
+++ b/drivers/net/mctp/mctp-i2c.c
@@ -588,6 +588,9 @@ static int mctp_i2c_header_create(struct sk_buff *skb, struct net_device *dev,
 	if (len > MCTP_I2C_MAXMTU)
 		return -EMSGSIZE;
 
+	if (!daddr || !saddr)
+		return -EINVAL;
+
 	lldst = *((u8 *)daddr);
 	llsrc = *((u8 *)saddr);
 

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

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