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Re: [Xen-devel] [PATCH 2/4] xen-netfront: drop skb when skb->len > 65535
On 09.04.13 16:45, Ben Hutchings wrote:
On Tue, 2013-04-09 at 15:30 +0100, Ian Campbell wrote:
On Tue, 2013-03-19 at 21:28 +0000, Ben Hutchings wrote:
On Tue, 2013-03-19 at 21:24 +0000, Ben Hutchings wrote:
On Mon, 2013-03-18 at 15:07 +0000, Ian Campbell wrote:
On Mon, 2013-03-18 at 15:04 +0000, Wei Liu wrote:
On Mon, 2013-03-18 at 14:54 +0000, Ian Campbell wrote:
On Mon, 2013-03-18 at 14:40 +0000, Wei Liu wrote:
On Mon, 2013-03-18 at 11:42 +0000, Ian Campbell wrote:
On Mon, 2013-03-18 at 10:35 +0000, Wei Liu wrote:
The `size' field of Xen network wire format is uint16_t, anything bigger than
65535 will cause overflow.
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
drivers/net/xen-netfront.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 5527663..8c3d065 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -547,6 +547,18 @@ static int xennet_start_xmit(struct sk_buff *skb, struct
net_device *dev)
unsigned int len = skb_headlen(skb);
unsigned long flags;
+ /*
+ * wire format of xen_netif_tx_request only supports skb->len
+ * < 64K, because size field in xen_netif_tx_request is
+ * uint16_t.
Is there some field we can set e.g. in struct ethernet_device which
would stop this from happening?
struct ethernet_device? I could not find it.
And for struct net_device,
I meant struct net_device.
there is no field for this AFAICT.
Interesting. Are hardware devices expected to cope with arbitrary sized
GSO skbs then I wonder.
No idea. But there is a macro called GSO_MAX_SIZE (65536) in struct
net_device. :-)
But aren't we seeing skb's bigger than that?
Maybe this is just a historical bug in some older guests?
GSO_MAX_SIZE is the maximum payload length, not the maximum total length
of an skb.
...and it's actually just the default value assigned to
dev->gso_max_size. You'll want to change it to your actual maximum
(65535 - maximum length of headers) before registering your net devices.
Thanks.
"maximum length of headers" might be a bit tricky to determine
generically :-(.
Well you don't need to be generic, you need to know the maximum length
of headers that might appear in a TSO skb.
Ethernet + VLAN tag + IPv6 + TCP + timestamp option = 90 bytes, but I'm
not sure whether there can be other IP or TCP options in a TSO skb. I'd
really like to get the TSO requirements clearly documented somewhere.
What about encapsulated IPSEC, IP-in-IP-tunnels, etc. ?
Christoph
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