[PATCH 3.16 174/305] can: raw: check for CAN FD capable netdev in raw_sendmsg()

[Ben Hutchings]

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>

commit a43608fa77213ad5ac5f75994254b9f65d57cfa0 upstream.

When the socket is CAN FD enabled it can handle CAN FD frame
transmissions.  Add an additional check in raw_sendmsg() as a CAN2.0 CAN
driver (non CAN FD) should never see a CAN FD frame. Due to the commonly
used can_dropped_invalid_skb() function the CAN 2.0 driver would drop
that CAN FD frame anyway - but with this patch the user gets a proper
-EINVAL return code.

Signed-off-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
[bwh: Backported to 3.16: Keep looking up devices in init_net]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/can/raw.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -686,18 +686,19 @@ static int raw_sendmsg(struct kiocb *ioc
 	} else
 		ifindex = ro->ifindex;
 
-	if (ro->fd_frames) {
+	dev = dev_get_by_index(&init_net, ifindex);
+	if (!dev)
+		return -ENXIO;
+
+	err = -EINVAL;
+	if (ro->fd_frames && dev->mtu == CANFD_MTU) {
 		if (unlikely(size != CANFD_MTU && size != CAN_MTU))
-			return -EINVAL;
+			goto put_dev;
 	} else {
 		if (unlikely(size != CAN_MTU))
-			return -EINVAL;
+			goto put_dev;
 	}
 
-	dev = dev_get_by_index(&init_net, ifindex);
-	if (!dev)
-		return -ENXIO;
-
 	skb = sock_alloc_send_skb(sk, size + sizeof(struct can_skb_priv),
 				  msg->msg_flags & MSG_DONTWAIT, &err);
 	if (!skb)