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Subject[PATCH 4.9 33/44] can: dev: __can_get_echo_skb(): fix bogous check for non-existing skb by removing it
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Manfred Schlaegl <manfred.schlaegl@ginzinger.com>

commit 7b12c8189a3dc50638e7d53714c88007268d47ef upstream.

This patch revert commit 7da11ba5c506
("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: 7da11ba5c506 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/net/can/dev.c | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)

--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c
@@ -456,8 +456,6 @@ 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",
@@ -465,20 +463,21 @@ struct sk_buff *__can_get_echo_skb(struc
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.
+ */
+ struct sk_buff *skb = priv->echo_skb[idx];
+ struct canfd_frame *cf = (struct canfd_frame *)skb->data;
+ u8 len = cf->len;

- /* 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;
+ *len_ptr = len;
+ priv->echo_skb[idx] = NULL;
+
+ return skb;
+ }

- return skb;
+ return NULL;
}

/*

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