[PATCH v2 1/4] can: kvaser_usb: Don't free packets when tight on URBs

From: Ahmed S. Darwish
Date: Wed Dec 24 2014 - 20:57:23 EST

From: Ahmed S. Darwish <ahmed.darwish@xxxxxxxxx>

Flooding the Kvaser CAN to USB dongle with multiple reads and
writes in high frequency caused seemingly-random panics in the

On further inspection, it seems the driver erroneously freed the
to-be-transmitted packet upon getting tight on URBs and returning
NETDEV_TX_BUSY, leading to invalid memory writes and double frees
at a later point in time.


Finding no more URBs/transmit-contexts and returning NETDEV_TX_BUSY
is a driver bug in and out of itself: it means that our start/stop
queue flow control is broken.

This patch only fixes the (buggy) error handling code; the root
cause shall be fixed in a later commit.

Signed-off-by: Ahmed S. Darwish <ahmed.darwish@xxxxxxxxx>
drivers/net/can/usb/kvaser_usb.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

(Marc, Greg, I believe this should also be added to -stable?)

diff --git a/drivers/net/can/usb/kvaser_usb.c b/drivers/net/can/usb/kvaser_usb.c
index 541fb7a..6479a2b 100644
--- a/drivers/net/can/usb/kvaser_usb.c
+++ b/drivers/net/can/usb/kvaser_usb.c
@@ -1294,12 +1294,14 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb,
if (!urb) {
netdev_err(netdev, "No memory left for URBs\n");
- goto nourbmem;
+ dev_kfree_skb(skb);
+ return NETDEV_TX_OK;

buf = kmalloc(sizeof(struct kvaser_msg), GFP_ATOMIC);
if (!buf) {
+ dev_kfree_skb(skb);
goto nobufmem;

@@ -1334,6 +1336,9 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb,

+ /*
+ * This should never happen; it implies a flow control bug.
+ */
if (!context) {
netdev_warn(netdev, "cannot find free context\n");
@@ -1364,9 +1369,6 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb,
if (unlikely(err)) {
can_free_echo_skb(netdev, context->echo_index);

- skb = NULL; /* set to NULL to avoid double free in
- * dev_kfree_skb(skb) */

@@ -1388,8 +1390,6 @@ releasebuf:
- dev_kfree_skb(skb);
return ret;

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