[ 064/102] asix: fix BUG in receive path when lowering MTU

From: Greg Kroah-Hartman
Date: Fri May 17 2013 - 18:12:23 EST

3.9-stable review patch. If anyone has any objections, please let me know.


From: "holger@xxxxxxxxxxxxxxxx" <holger@xxxxxxxxxxxxxxxx>

[ Upstream commit c5060cec6ba27ad3f0e7facfdf05d2f18e3e3010 ]

There is bug in the receive path of the asix driver at the time a
packet is received larger than MTU size and DF bit set:

BUG: unable to handle kernel paging request at 0000004000000001
IP: [<ffffffff8126f65b>] skb_release_head_state+0x2d/0xd2
Call Trace:
[<ffffffff8126f86d>] ? skb_release_all+0x9/0x1e
[<ffffffff8126f8ad>] ? __kfree_skb+0x9/0x6f
[<ffffffffa00b4200>] ? asix_rx_fixup_internal+0xff/0x1ae [asix]
[<ffffffffa00fb3dc>] ? usbnet_bh+0x4f/0x226 [usbnet]

It is easily reproducable by setting an MTU of 512 e. g. and sending
something like

ping -s 1472 -c 1 -M do $SELF

from another box.

And this is because the rx->ax_skb is freed on error, but rx->ax_skb
is not reset, and the size is not reset to zero in this case.

And since the skb is added again to the usbnet->done skb queue it is
accessing already freed memory, resulting in the BUG when freeing a
2nd time. I therefore think the value 0x0000004000000001 show in the
trace is more or less random data.

Signed-off-by: Holger Eitzenberger <holger@xxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
drivers/net/usb/asix_common.c | 3 +++
1 file changed, 3 insertions(+)

--- a/drivers/net/usb/asix_common.c
+++ b/drivers/net/usb/asix_common.c
@@ -100,6 +100,9 @@ int asix_rx_fixup_internal(struct usbnet
netdev_err(dev->net, "asix_rx_fixup() Bad RX Length %d\n",
+ rx->ax_skb = NULL;
+ rx->size = 0U;
return 0;

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/