netdev - Re: [PATCH V2] ipv6 mcast: Fix incorrect use of pskb_may

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Date:	Wed, 26 Dec 2012 08:03:12 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
Cc:	"'netdev@...r.kernel.org'" <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH V2] ipv6 mcast: Fix incorrect use of pskb_may_pull().

On Wed, 2012-12-26 at 12:12 +0900, YOSHIFUJI Hideaki wrote:
> pskb_may_pull(skb, len) ensures that len bytes from skb->data
> are available in a linear array.  When pskb_may_pull() is
> being used multiple times for the same buffer without
> skb_pull(), the length is not accumulated.
> 
> For example, assuming that we have done:
>   pskb_may_pull(skb, sizeof(struct icmp6hdr))
> 
> Here, we have to do:
>   pskb_may_pull(skb, sizeof(struct mld2_query))
> instead of:
>   pskb_may_pull(skb, sizeof(struct mld2_query) -
>                 sizeof(struct icmp6hdr))
> 
> Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
> ---
>  net/ipv6/mcast.c |   13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
> index 28dfa5f..5d91832 100644
> --- a/net/ipv6/mcast.c
> +++ b/net/ipv6/mcast.c
> @@ -1124,7 +1124,7 @@ int igmp6_event_query(struct sk_buff *skb)
>  	int mark = 0;
>  	int len;
>  
> -	if (!pskb_may_pull(skb, sizeof(struct in6_addr)))
> +	if (!pskb_may_pull(skb, sizeof(struct icmp6hdr) + sizeof(struct in6_addr)))
>  		return -EINVAL;
>  

I am a bit confused by your patch.

igmp6_event_query() is called from icmpv6_rcv() _after_ 

pskb_pull(skb, sizeof(*hdr);

(hdr being struct icmp6hdr)

So this patch is wrong IMHO




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