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Re: [Xen-devel] [PATCH net v2] xen-netback: fix fragment detection in checksum setup

On 2013/11/29 17:10, Paul Durrant wrote:
-----Original Message-----
From: annie li [mailto:annie.li@xxxxxxxxxx]
Sent: 29 November 2013 05:36
To: Paul Durrant
Cc: xen-devel@xxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; Wei Liu; Ian Campbell;
David Vrabel
Subject: Re: [PATCH net v2] xen-netback: fix fragment detection in checksum

On 2013/11/28 21:23, Paul Durrant wrote:
The code to detect fragments in checksum_setup() was missing for IPv4
too eager for IPv6. (It transpires that Windows seems to send IPv6 packets
with a fragment header even if they are not a fragment - i.e. offset is zero,
and M bit is not set).

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>

- Added comments noting what fragment/offset masks mean

   drivers/net/xen-netback/netback.c |   33
   1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-
index 919b650..c7464d8 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1165,15 +1165,28 @@ static int checksum_setup_ip(struct xenvif *vif,
struct sk_buff *skb,
        struct iphdr *iph = (void *)skb->data;
        unsigned int header_size;
        unsigned int off;
+       bool fragment;
        int err = -EPROTO;

+       fragment = false;
Is it better to initialize fragment directly as following?
bool fragment = false;

I think that's a matter of personal taste. I tend to favour this style.

That is OK, I point this out because it is inconsistent with other variable initialization in netback.c.


        off = sizeof(struct iphdr);

        header_size = skb->network_header + off + MAX_IPOPTLEN;
        maybe_pull_tail(skb, header_size);

+       /* 3fff -> fragment offset != 0 OR more fragments */
+       if (ntohs(iph->frag_off) & 0x3fff)
+               fragment = true;
        off = iph->ihl * 4;

+       if (fragment) {
+               if (net_ratelimit())
+                       netdev_err(vif->dev, "Packet is a fragment!\n");
+               goto out;
+       }
        switch (iph->protocol) {
        case IPPROTO_TCP:
                if (!skb_partial_csum_set(skb, off,
@@ -1237,6 +1250,7 @@ static int checksum_setup_ipv6(struct xenvif *vif,
struct sk_buff *skb,
        bool fragment;
        bool done;

+       fragment = false;
        done = false;
Same as above for "done" and "fragment"...

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