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    Subject[064/141] xen-netfront: reduce gso_max_size to account for max TCP header
    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 9ecd1a75d977e2e8c48139c7d3efed183f898d94 ]

    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@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-netfront.c | 17 +++++++++++++++--
    include/xen/interface/io/netif.h | 1 +
    2 files changed, 16 insertions(+), 2 deletions(-)

    diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
    index 650f79a..ecac034 100644
    --- a/drivers/net/xen-netfront.c
    +++ b/drivers/net/xen-netfront.c
    @@ -36,7 +36,7 @@
    #include <linux/skbuff.h>
    #include <linux/ethtool.h>
    #include <linux/if_ether.h>
    -#include <linux/tcp.h>
    +#include <net/tcp.h>
    #include <linux/udp.h>
    #include <linux/moduleparam.h>
    #include <linux/mm.h>
    @@ -491,6 +491,16 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
    unsigned int len = skb_headlen(skb);
    unsigned long flags;

    + /* 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)) {
    + net_alert_ratelimited(
    + "xennet: skb->len = %u, too big for wire format\n",
    + skb->len);
    + goto drop;
    + }
    +
    frags += DIV_ROUND_UP(offset + len, PAGE_SIZE);
    if (unlikely(frags > MAX_SKB_FRAGS + 1)) {
    printk(KERN_ALERT "xennet: skb rides the rocket: %d frags\n",
    @@ -1026,7 +1036,8 @@ err:

    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;
    @@ -1330,6 +1341,8 @@ static struct net_device * __devinit xennet_create_dev(struct xenbus_device *dev
    SET_ETHTOOL_OPS(netdev, &xennet_ethtool_ops);
    SET_NETDEV_DEV(netdev, &dev->dev);

    + netif_set_gso_max_size(netdev, XEN_NETIF_MAX_TX_SIZE - MAX_TCP_HEADER);
    +
    np->netdev = netdev;

    netif_carrier_off(netdev);
    diff --git a/include/xen/interface/io/netif.h b/include/xen/interface/io/netif.h
    index a36c87a..d4635cd 100644
    --- a/include/xen/interface/io/netif.h
    +++ b/include/xen/interface/io/netif.h
    @@ -65,6 +65,7 @@
    #define _XEN_NETTXF_extra_info (3)
    #define XEN_NETTXF_extra_info (1U<<_XEN_NETTXF_extra_info)

    +#define XEN_NETIF_MAX_TX_SIZE 0xFFFF
    struct xen_netif_tx_request {
    grant_ref_t gref; /* Reference to buffer page */
    uint16_t offset; /* Offset within buffer page */
    --
    1.7.10.4



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