netdev - Re: [PATCH] net: Initialize entire flowi struct

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Date:	Thu, 1 Sep 2011 09:34:27 -0400
From:	"Ward, David - 0663 - MITLL" <david.ward@...mit.edu>
To:	Julian Anastasov <ja@....bg>
CC:	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: Initialize entire flowi struct

Hi Julian,

On 08/31/2011 04:51 PM, Julian Anastasov wrote:
> On Wed, 31 Aug 2011, David Ward wrote
>> The entire flowi struct needs to be initialized by afinfo->decode_session,
>> because flow_hash_code operates over the entire struct and may otherwise
>> return different hash values for what is intended to be the same key.
> 	Such change will cause problems for callers that
> use flowi4 in stack. Examples:
>
> ip_route_me_harder
> icmp_route_lookup

Thanks for pointing this out.

> 	Not sure if adding size as parameter to flow_hash_code
> is better approach. May be flow_cache_lookup needs to
> determine size from family that can be used for flow_hash_code,
> flow_key_compare and the memcpy(&fle->key, key, sizeof(*key))
> after fle = kmem_cache_alloc(flow_cachep, GFP_ATOMIC).

Makes sense to me.  However should we just replace flow_key_compare with 
memcmp then, since the assumptions about constant size and alignment 
will no longer apply?  Or should there be a separate flow_key_compare 
function for each family, and have all of the flowi* structures become 
__attribute__((__aligned__(BITS_PER_LONG/8))) ?

David

> The question is how to get size by family.
>
>> Signed-off-by: David Ward<david.ward@...mit.edu>
>> ---
>>   net/ipv4/xfrm4_policy.c |    2 +-
>>   net/ipv6/xfrm6_policy.c |    2 +-
>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/ipv4/xfrm4_policy.c b/net/ipv4/xfrm4_policy.c
>> index fc5368a..afce24d 100644
>> --- a/net/ipv4/xfrm4_policy.c
>> +++ b/net/ipv4/xfrm4_policy.c
>> @@ -114,7 +114,7 @@ _decode_session4(struct sk_buff *skb, struct flowi *fl, int reverse)
>>   	u8 *xprth = skb_network_header(skb) + iph->ihl * 4;
>>   	struct flowi4 *fl4 =&fl->u.ip4;
>>
>> -	memset(fl4, 0, sizeof(struct flowi4));
>> +	memset(fl, 0, sizeof(struct flowi));
>>   	fl4->flowi4_mark = skb->mark;
>>
>>   	if (!ip_is_fragment(iph)) {
>> diff --git a/net/ipv6/xfrm6_policy.c b/net/ipv6/xfrm6_policy.c
>> index d879f7e..9088d38 100644
>> --- a/net/ipv6/xfrm6_policy.c
>> +++ b/net/ipv6/xfrm6_policy.c
>> @@ -129,7 +129,7 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
>>   	const unsigned char *nh = skb_network_header(skb);
>>   	u8 nexthdr = nh[IP6CB(skb)->nhoff];
>>
>> -	memset(fl6, 0, sizeof(struct flowi6));
>> +	memset(fl, 0, sizeof(struct flowi));
>>   	fl6->flowi6_mark = skb->mark;
>>
>>   	ipv6_addr_copy(&fl6->daddr, reverse ?&hdr->saddr :&hdr->daddr);
>> -- 
>> 1.7.4.1


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