linux-kernel - [PATCH 4.9 12/78] can: dev: __can_get_echo_skb(): fix real payload length return value for RTR frames

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Message-Id: <20201117122109.705386592@linuxfoundation.org>
Date:   Tue, 17 Nov 2020 14:04:38 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 12/78] can: dev: __can_get_echo_skb(): fix real payload length return value for RTR frames

From: Oliver Hartkopp <socketcan@...tkopp.net>

[ Upstream commit ed3320cec279407a86bc4c72edc4a39eb49165ec ]

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@...adoo.fr>
Signed-off-by: Oliver Hartkopp <socketcan@...tkopp.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@...gutronix.de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 aa2158fabf2ac..617eb75c7c0ce 100644
--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c
@@ -469,9 +469,13 @@ struct sk_buff *__can_get_echo_skb(struct net_device *dev, unsigned int idx, u8
 		 */
 		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;
-- 
2.27.0