From ed3320cec279407a86bc4c72edc4a39eb49165ec Mon Sep 17 00:00:00 2001
From: Oliver Hartkopp <socketcan@hartkopp.net>
Date: Tue, 20 Oct 2020 08:44:43 +0200
Subject: [PATCH] can: dev: __can_get_echo_skb(): fix real payload length return value for RTR frames
Git-commit: ed3320cec279407a86bc4c72edc4a39eb49165ec
Patch-mainline: v5.10-rc3
References: git-fixes

The can_get_echo_skb() function returns the number of received bytes to
be used for netdev statistics. In the case of RTR frames we get a valid
(potential non-zero) data length value which has to be passed for further
operations. But on the wire RTR frames have no payload length. Therefore
the value to be used in the statistics has to be zero for RTR frames.

Reported-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/r/20201020064443.80164-1-socketcan@hartkopp.net
Fixes: cf5046b309b3 ("can: dev: let can_get_echo_skb() return dlc of CAN frame")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/net/can/dev.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index 73cfcd7e9517..6dee4f8f2024 100644
--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c
@@ -512,9 +512,13 @@ __can_get_echo_skb(struct net_device *dev, unsigned int idx, u8 *len_ptr)
 		 */
 		struct sk_buff *skb = priv->echo_skb[idx];
 		struct canfd_frame *cf = (struct canfd_frame *)skb->data;
-		u8 len = cf->len;
 
-		*len_ptr = len;
+		/* get the real payload length for netdev statistics */
+		if (cf->can_id & CAN_RTR_FLAG)
+			*len_ptr = 0;
+		else
+			*len_ptr = cf->len;
+
 		priv->echo_skb[idx] = NULL;
 
 		return skb;
-- 
2.16.4