[061/141] xen-netback: dont disconnect frontend when seeing oversize packet

Steven Rostedt
2013-07-03T18:43:38Z

[-- Attachment #1: 0061-xen-netback-don-t-disconnect-frontend-when-seeing-ov.patch --]
[-- Type: text/plain, Size: 2158 bytes --]

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

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

From: Wei Liu <wei.liu2@citrix.com>

[ Upstream commit 03393fd5cc2b6cdeec32b704ecba64dbb0feae3c ]

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>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
drivers/net/xen-netback/netback.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index d5a4e74..89dd960 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -946,12 +946,22 @@ 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;
--
1.7.10.4