Re: [syzbot] Test for 5681e40d297b30f5b513

[syzbot <syzbot+5681e40d297b30f5b513@syzkaller.appspotmail.com>]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: Test for 5681e40d297b30f5b513
Author: syoshida@redhat.com

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 71b1543c83d65af8215d7558d70fc2ecbee77dcf

diff --git a/net/can/j1939/main.c b/net/can/j1939/main.c
index a6fb89fa6278..7e8a20f2fc42 100644
--- a/net/can/j1939/main.c
+++ b/net/can/j1939/main.c
@@ -30,10 +30,6 @@ MODULE_ALIAS("can-proto-" __stringify(CAN_J1939));
 /* CAN_HDR: #bytes before can_frame data part */
 #define J1939_CAN_HDR (offsetof(struct can_frame, data))
 
-/* CAN_FTR: #bytes beyond data part */
-#define J1939_CAN_FTR (sizeof(struct can_frame) - J1939_CAN_HDR - \
-		 sizeof(((struct can_frame *)0)->data))
-
 /* lowest layer */
 static void j1939_can_recv(struct sk_buff *iskb, void *data)
 {
@@ -342,7 +338,7 @@ int j1939_send_one(struct j1939_priv *priv, struct sk_buff *skb)
 	memset(cf, 0, J1939_CAN_HDR);
 
 	/* make it a full can frame again */
-	skb_put(skb, J1939_CAN_FTR + (8 - dlc));
+	skb_put_zero(skb, 8 - dlc);
 
 	canid = CAN_EFF_FLAG |
 		(skcb->priority << 26) |