Commit 7b12c818 authored Dec 19, 2018 by Manfred Schlaegl Committed by Marc Kleine-Budde Jan 22, 2019

can: dev: __can_get_echo_skb(): fix bogous check for non-existing skb by removing it



This patch revert commit 7da11ba5
("can: dev: __can_get_echo_skb(): print error message, if trying to echo non existing skb")

After introduction of this change we encountered following new error
message on various i.MX plattforms (flexcan):

| flexcan 53fc8000.can can0: __can_get_echo_skb: BUG! Trying to echo non
| existing skb: can_priv::echo_skb[0]

The introduction of the message was a mistake because
priv->echo_skb[idx] = NULL is a perfectly valid in following case: If
CAN_RAW_LOOPBACK is disabled (setsockopt) in applications, the pkt_type
of the tx skb's given to can_put_echo_skb is set to PACKET_LOOPBACK. In
this case can_put_echo_skb will not set priv->echo_skb[idx]. It is
therefore kept NULL.

As additional argument for revert: The order of check and usage of idx
was changed. idx is used to access an array element before checking it's
boundaries.

Signed-off-by: Manfred Schlaegl <manfred.schlaegl@ginzinger.com>
Fixes: 7da11ba5 ("can: dev: __can_get_echo_skb(): print error message, if trying to echo non existing skb")
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

parent 49a57857

drivers/net/can/dev.c

+13 −14

Original line number	Diff line number	Diff line
		@@ -480,8 +480,6 @@ 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",
		@@ -489,22 +487,23 @@ struct sk_buff __can_get_echo_skb(struct net_device dev, unsigned int idx, u8
		return NULL;
		}

		if (!skb) {
		netdev_err(dev, "%s: BUG! Trying to echo non existing skb: can_priv::echo_skb[%u]\n",
		__func__, idx);
		return NULL;
		}

		if (priv->echo_skb[idx]) {
		/* 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;
		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;
		}

		return NULL;
		}

		/*
		* Get the skb from the stack and loop it back locally
		*

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