[ 121/127] xen-netback: dont disconnect frontend when seeing oversize packet

From: Greg Kroah-Hartman
Date: Wed Jun 05 2013 - 17:39:43 EST


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

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

From: Wei Liu <wei.liu2@xxxxxxxxxx>

commit 03393fd5cc2b6cdeec32b704ecba64dbb0feae3c upstream.

Some frontend drivers are sending packets > 64 KiB in length. This length
overflows the length field in the first slot making the following slots have
an invalid length.

Turn this error back into a non-fatal error by dropping the packet. To avoid
having the following slots having fatal errors, consume all slots in the
packet.

This does not reopen the security hole in XSA-39 as if the packet as an
invalid number of slots it will still hit fatal error case.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
drivers/net/xen-netback/netback.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)

--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -975,12 +975,22 @@ static int netbk_count_requests(struct x

memcpy(txp, RING_GET_REQUEST(&vif->tx, cons + slots),
sizeof(*txp));
- if (txp->size > first->size) {
- netdev_err(vif->dev,
- "Invalid tx request, slot size %u > remaining size %u\n",
- txp->size, first->size);
- netbk_fatal_tx_err(vif);
- return -EIO;
+
+ /* If the guest submitted a frame >= 64 KiB then
+ * first->size overflowed and following slots will
+ * appear to be larger than the frame.
+ *
+ * This cannot be fatal error as there are buggy
+ * frontends that do this.
+ *
+ * Consume all slots and drop the packet.
+ */
+ if (!drop_err && txp->size > first->size) {
+ if (net_ratelimit())
+ netdev_dbg(vif->dev,
+ "Invalid tx request, slot size %u > remaining size %u\n",
+ txp->size, first->size);
+ drop_err = -EIO;
}

first->size -= txp->size;


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