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

From: annie li <[email-masked]>
Date: Fri, 29 Nov 2013 17:57:03 +0800

On 2013/11/29 17:10, Paul Durrant wrote:
>> -----Original Message-----
>> From: annie li [mailto:[email-masked]]
>> Sent: 29 November 2013 05:36
>> To: Paul Durrant
>> Cc: [email-masked]; [email-masked]; Wei Liu; Ian Campbell;
>> David Vrabel
>> Subject: Re: [PATCH net v2] xen-netback: fix fragment detection in checksum
>> setup
>>
>>
>> On 2013/11/28 21:23, Paul Durrant wrote:
>>> The code to detect fragments in checksum_setup() was missing for IPv4
>> and
>>> 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 <[email-masked]>
>>> Cc: Wei Liu <[email-masked]>
>>> Cc: Ian Campbell <[email-masked]>
>>> Cc: David Vrabel <[email-masked]>
>>> ---
>>> v2
>>>
>>> - 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-
>> netback/netback.c
>>> 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.

Thanks
Annie
>
>>> +
>>>    	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"...
>>
>> Thanks
>> Annie
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