xen-netback: don't disconnect frontend when seeing oversize packet

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@citrix.com>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index d9292c5..a2865f1 100644 (file)
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -975,12 +975,22 @@ static int netbk_count_requests(struct xenvif *vif,
 
                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;