can: isotp: tx-path: zero initialize outgoing CAN frames

Commit d4eb538e1f48 ("can: isotp: TX-path: ensure that CAN frame flags are
initialized") ensured the TX flags to be properly set for outgoing CAN
frames.

In fact the root cause of the issue results from a missing initialization
of outgoing CAN frames created by isotp. This is no problem on the CAN bus
as the CAN driver only picks the correctly defined content from the struct
can(fd)_frame. But when the outgoing frames are monitored (e.g. with
candump) we potentially leak some bytes in the unused content of
struct can(fd)_frame.

Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
Cc: Marc Kleine-Budde <[email protected]>
Signed-off-by: Oliver Hartkopp <[email protected]>

Author: hartkopp

net/can/isotp.c

@@ -231,6 +231,7 @@ static int isotp_send_fc(struct sock *sk, int ae, u8 flowstatus)
 	isotp_skb_set_owner(nskb, sk);
 	ncf = (struct canfd_frame *) nskb->data;
 	skb_put(nskb, so->ll.mtu);
+	memset(ncf, 0, so->ll.mtu);
 
 	/* create & send flow control reply */
 	ncf->can_id = so->txid;
@@ -789,6 +790,7 @@ static void isotp_tx_timer_tsklet(unsigned long data)
 		isotp_skb_reserve(skb, dev);
 		cf = (struct canfd_frame *)skb->data;
 		skb_put(skb, so->ll.mtu);
+		memset(cf, 0, so->ll.mtu);
 
 		/* create consecutive frame */
 		isotp_fill_dataframe(cf, so, ae, 0);
@@ -921,6 +923,7 @@ static int isotp_sendmsg(struct kiocb *iocb, struct socket *sock,
 
 	cf = (struct canfd_frame *)skb->data;
 	skb_put(skb, so->ll.mtu);
+	memset(cf, 0, so->ll.mtu);
 
 	/* check for single frame transmission depending on TX_DL */
 	if (size <= so->tx.ll_dl - SF_PCI_SZ4 - ae - off) {