[PATCH] can: j1939: fix missing CAN header initialization

[Oliver Hartkopp <socketcan@hartkopp.net>]

The read access to struct canxl_frame::len inside of a j1939 created skbuff
revealed a missing initialization of reserved and later filled elements in
struct can_frame.

This patch initializes the 8 byte CAN header with zero.

Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Cc: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/linux-can/20221104052235.GA6474@pengutronix.de/T/#t
Reported-by: syzbot+d168ec0caca4697e03b1@syzkaller.appspotmail.com
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 net/can/j1939/main.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/can/j1939/main.c b/net/can/j1939/main.c
index 144c86b0e3ff..821d4ff303b3 100644
--- a/net/can/j1939/main.c
+++ b/net/can/j1939/main.c
@@ -334,10 +334,13 @@ int j1939_send_one(struct j1939_priv *priv, struct sk_buff *skb)
 	dlc = skb->len;
 
 	/* re-claim the CAN_HDR from the SKB */
 	cf = skb_push(skb, J1939_CAN_HDR);
 
+	/* initialize header structure */
+	memset(cf, 0, J1939_CAN_HDR);
+
 	/* make it a full can frame again */
 	skb_put(skb, J1939_CAN_FTR + (8 - dlc));
 
 	canid = CAN_EFF_FLAG |
 		(skcb->priority << 26) |
-- 
2.30.2