[Xen-changelog] [linux-2.6.18-xen] netfront: reduce gso_max_size to account for max TCP header

[Xen patchbot-linux-2.6.18-xen <patchbot@xxxxxxx>]

# HG changeset patch
# User Wei Liu <wei.liu2@xxxxxxxxxx>
# Date 1367332425 -7200
# Node ID 5e80033562fa444531ba87e51c7d8cc45c93715b
# Parent  03152e80954136f7eb4ea37c7dc358024a45888f
netfront: reduce gso_max_size to account for max TCP header

The maximum packet including header that can be handled by netfront / netback
wire format is 65535. Reduce gso_max_size accordingly.

Drop skb and print warning when skb->len > 65535. This can 1) save the effort
to send malformed packet to netback, 2) help spotting misconfiguration of
netfront in the future.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Committed-by: Jan Beulich <jbeulich@xxxxxxxx>
---


diff -r 03152e809541 -r 5e80033562fa drivers/xen/netfront/netfront.c
--- a/drivers/xen/netfront/netfront.c   Tue Apr 30 16:30:31 2013 +0200
+++ b/drivers/xen/netfront/netfront.c   Tue Apr 30 16:33:45 2013 +0200
@@ -52,6 +52,7 @@
 #include <net/pkt_sched.h>
 #include <net/arp.h>
 #include <net/route.h>
+#include <net/tcp.h>
 #include <asm/uaccess.h>
 #include <xen/evtchn.h>
 #include <xen/xenbus.h>
@@ -960,6 +961,16 @@ static int network_start_xmit(struct sk_
                return 0; 
        } 
 
+       /*
+        * If skb->len is too big for wire format, drop skb and alert
+        * user about misconfiguration.
+        */
+       if (unlikely(skb->len > XEN_NETIF_MAX_TX_SIZE)) {
+               printk(KERN_ALERT "xennet: length %u too big for interface\n",
+                      skb->len);
+               goto drop;
+       }
+
        frags += (offset + len + PAGE_SIZE - 1) / PAGE_SIZE;
        if (unlikely(frags > MAX_SKB_FRAGS + 1)) {
                printk(KERN_ALERT "xennet: skb rides the rocket: %d frags\n",
@@ -1709,7 +1720,8 @@ static int xennet_set_mac_address(struct
 
 static int xennet_change_mtu(struct net_device *dev, int mtu)
 {
-       int max = xennet_can_sg(dev) ? 65535 - ETH_HLEN : ETH_DATA_LEN;
+       int max = xennet_can_sg(dev) ? XEN_NETIF_MAX_TX_SIZE - MAX_TCP_HEADER
+                                    : ETH_DATA_LEN;
 
        if (mtu > max)
                return -EINVAL;
@@ -2111,6 +2123,10 @@ static struct net_device * __devinit cre
        SET_MODULE_OWNER(netdev);
        SET_NETDEV_DEV(netdev, &dev->dev);
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,26)
+       netif_set_gso_max_size(netdev, XEN_NETIF_MAX_TX_SIZE - MAX_TCP_HEADER);
+#endif
+
        np->netdev = netdev;
 
        netfront_carrier_off(np);
diff -r 03152e809541 -r 5e80033562fa include/xen/interface/io/netif.h
--- a/include/xen/interface/io/netif.h  Tue Apr 30 16:30:31 2013 +0200
+++ b/include/xen/interface/io/netif.h  Tue Apr 30 16:33:45 2013 +0200
@@ -71,6 +71,7 @@ struct netif_tx_request {
     uint16_t flags;        /* NETTXF_* */
     uint16_t id;           /* Echoed in response message. */
     uint16_t size;         /* Packet size in bytes.       */
+#define XEN_NETIF_MAX_TX_SIZE 0xFFFF
 };
 typedef struct netif_tx_request netif_tx_request_t;
 

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