[ 3.8.y.z extended stable ] Patch "xen-netback: don't disconnect frontend when seeing oversize packet" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.4.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 5c38697aec31e83ba53da34b15be921c2059fa8b Mon Sep 17 00:00:00 2001
From: Wei Liu <wei.liu2 at citrix.com>
Date: Mon, 22 Apr 2013 02:20:43 +0000
Subject: xen-netback: don't disconnect frontend when seeing oversize packet

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 at citrix.com>
Signed-off-by: Wei Liu <wei.liu2 at citrix.com>
Acked-by: Ian Campbell <ian.campbell at citrix.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 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 2b50c67..b74bc4f 100644
--- 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;
--
1.8.1.2