Wei Liu
2013-Apr-12 14:24 UTC
[PATCH V4 5/7] xen-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@citrix.com>
---
drivers/net/xen-netfront.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 1bb2e20..9c2eca1 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -547,6 +547,16 @@ 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 > (typeof(tx->size))(~0))) {
+ net_alert_ratelimited(
+ "xennet: skb->len = %u, too big for wire format\n",
+ skb->len);
+ goto drop;
+ }
+
slots = DIV_ROUND_UP(offset + len, PAGE_SIZE) +
xennet_count_skb_frag_slots(skb);
if (unlikely(slots > MAX_SKB_FRAGS + 1)) {
@@ -1058,7 +1068,7 @@ 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) ? 65535 - MAX_TCP_HEADER : ETH_DATA_LEN;
if (mtu > max)
return -EINVAL;
@@ -1362,6 +1372,8 @@ static struct net_device *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, 65535 - MAX_TCP_HEADER);
+
np->netdev = netdev;
netif_carrier_off(netdev);
--
1.7.10.4
Ian Campbell
2013-Apr-12 14:44 UTC
Re: [PATCH V4 5/7] xen-netfront: reduce gso_max_size to account for max TCP header
On Fri, 2013-04-12 at 15:24 +0100, Wei Liu wrote:> 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> > --- > drivers/net/xen-netfront.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c > index 1bb2e20..9c2eca1 100644 > --- a/drivers/net/xen-netfront.c > +++ b/drivers/net/xen-netfront.c > @@ -547,6 +547,16 @@ 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 > (typeof(tx->size))(~0))) {This seems rather a complicated way of saying... er, something! Perhaps we could have a #define in netif.h to compare against? I''m not 100% convinced that the case and the ~ are in the right order to have the behaviour you want unless perhaps sizeof(tx->size) < sizeof(int). In any case it''s too obfuscated for me ;-)> + net_alert_ratelimited( > + "xennet: skb->len = %u, too big for wire format\n", > + skb->len); > + goto drop; > + } > + > slots = DIV_ROUND_UP(offset + len, PAGE_SIZE) + > xennet_count_skb_frag_slots(skb); > if (unlikely(slots > MAX_SKB_FRAGS + 1)) { > @@ -1058,7 +1068,7 @@ 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) ? 65535 - MAX_TCP_HEADER : ETH_DATA_LEN; > > if (mtu > max) > return -EINVAL; > @@ -1362,6 +1372,8 @@ static struct net_device *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, 65535 - MAX_TCP_HEADER); > + > np->netdev = netdev; > > netif_carrier_off(netdev);
Jan Beulich
2013-Apr-12 15:07 UTC
Re: [PATCH V4 5/7] xen-netfront: reduce gso_max_size to account for max TCP header
>>> On 12.04.13 at 16:44, Ian Campbell <Ian.Campbell@citrix.com> wrote: > On Fri, 2013-04-12 at 15:24 +0100, Wei Liu wrote: >> 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> >> --- >> drivers/net/xen-netfront.c | 14 +++++++++++++- >> 1 file changed, 13 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c >> index 1bb2e20..9c2eca1 100644 >> --- a/drivers/net/xen-netfront.c >> +++ b/drivers/net/xen-netfront.c >> @@ -547,6 +547,16 @@ 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 > (typeof(tx->size))(~0))) { > > This seems rather a complicated way of saying... er, something! > > Perhaps we could have a #define in netif.h to compare against? > > I''m not 100% convinced that the case and the ~ are in the right order to > have the behaviour you want unless perhaps sizeof(tx->size) < > sizeof(int). In any case it''s too obfuscated for me ;-)Previously this was (u16)~0, which I complained to have no correlation to where the restriction actually comes from. Hence the request to use typeof() on the very field that doesn''t permit a larger value. Jan