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