[PATCH] can: kvaser_usb: Don't free packets when tight on URBs

Ahmed S. Darwish
2014-12-23T15:46:54Z

From: Ahmed S. Darwish <ahmed.darwish@valeo.com>

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

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.

Signed-off-by: Ahmed S. Darwish <ahmed.darwish@valeo.com>
---
drivers/net/can/usb/kvaser_usb.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

(Generated over 3.19.0-rc1)

diff --git a/drivers/net/can/usb/kvaser_usb.c b/drivers/net/can/usb/kvaser_usb.c
index 541fb7a..34c35d8 100644
--- a/drivers/net/can/usb/kvaser_usb.c
+++ b/drivers/net/can/usb/kvaser_usb.c
@@ -1286,6 +1286,7 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb,
struct kvaser_msg *msg;
int i, err;
int ret = NETDEV_TX_OK;
+ bool kfree_skb_on_error = true;

if (can_dropped_invalid_skb(netdev, skb))
return NETDEV_TX_OK;
@@ -1336,6 +1337,7 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb,

if (!context) {
netdev_warn(netdev, "cannot find free context\n");
+ kfree_skb_on_error = false;
ret = NETDEV_TX_BUSY;
goto releasebuf;
}
@@ -1364,8 +1366,7 @@ 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) */
+ kfree_skb_on_error = false;

atomic_dec(&priv->active_tx_urbs);
usb_unanchor_urb(urb);
@@ -1389,7 +1390,8 @@ releasebuf:
nobufmem:
usb_free_urb(urb);
nourbmem:
- dev_kfree_skb(skb);
+ if (kfree_skb_on_error)
+ dev_kfree_skb(skb);
return ret;
}