can: dev: __can_get_echo_skb(): print error message, if trying to echo non existing skb

commit 7da11ba5c5066dadc2e96835a6233d56d7b7764a upstream.

Prior to echoing a successfully transmitted CAN frame (by calling
can_get_echo_skb()), CAN drivers have to put the CAN frame (by calling
can_put_echo_skb() in the transmit function). These put and get function
take an index as parameter, which is used to identify the CAN frame.

A driver calling can_get_echo_skb() with a index not pointing to a skb
is a BUG, so add an appropriate error message.

Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index 7d61d88..035daca 100644 (file)
--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c
@@ -479,6 +479,8 @@ EXPORT_SYMBOL_GPL(can_put_echo_skb);
 struct sk_buff *__can_get_echo_skb(struct net_device *dev, unsigned int idx, u8 *len_ptr)
 {
        struct can_priv *priv = netdev_priv(dev);
+       struct sk_buff *skb = priv->echo_skb[idx];
+       struct canfd_frame *cf;
 
        if (idx >= priv->echo_skb_max) {
                netdev_err(dev, "%s: BUG! Trying to access can_priv::echo_skb out of bounds (%u/max %u)\n",
@@ -486,21 +488,20 @@ struct sk_buff *__can_get_echo_skb(struct net_device *dev, unsigned int idx, u8
                return NULL;
        }
 
-       if (priv->echo_skb[idx]) {
-               /* Using "struct canfd_frame::len" for the frame
-                * length is supported on both CAN and CANFD frames.
-                */
-               struct sk_buff *skb = priv->echo_skb[idx];
-               struct canfd_frame *cf = (struct canfd_frame *)skb->data;
-               u8 len = cf->len;
-
-               *len_ptr = len;
-               priv->echo_skb[idx] = NULL;
-
-               return skb;
+       if (!skb) {
+               netdev_err(dev, "%s: BUG! Trying to echo non existing skb: can_priv::echo_skb[%u]\n",
+                          __func__, idx);
+               return NULL;
        }
 
-       return NULL;
+       /* Using "struct canfd_frame::len" for the frame
+        * length is supported on both CAN and CANFD frames.
+        */
+       cf = (struct canfd_frame *)skb->data;
+       *len_ptr = cf->len;
+       priv->echo_skb[idx] = NULL;
+
+       return skb;
 }
 
 /*