netdev - Re: [PATCH net] ipv6: no CHECKSUM_PARTIAL on skbs with extension headers and recalc checksum during fragmentation

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Date:	Fri, 23 Oct 2015 15:48:45 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
	Vlad Yasevich <vyasevich@...il.com>,
	Benjamin Coddington <bcodding@...hat.com>
Subject: Re: [PATCH net] ipv6: no CHECKSUM_PARTIAL on skbs with extension
 headers and recalc checksum during fragmentation

On Fri, 2015-10-23 at 15:13 +0200, Hannes Frederic Sowa wrote:
> CHECKSUM_PARTIAL should only be used on plain vanilla IPv6 + UDP packets
> in ip6_append_data. Some drivers don't correctly handle extension headers,
> especially not ipv6 fragmentation which could result in broken checksums.
> 
> 1) This patch improves the test for fragmentation and extension headers
> in ip6_append_data, so we set the ip_summed mode as early as possible
> to the correct value to compute the checksum during memory copy-in from
> user space.
> 
> 2) We always call skb_checksum_help on CHECKSUM_PARTIAL fragments in
> ip6_fragment, because we don't know if the underlying hardware can deal
> with ip6_fragments.
> 
> Fixes: commit 32dce968dd987 ("ipv6: Allow for partial checksums on non-ufo packets")
> See-also: commit 72e843bb09d45 ("ipv6: ip6_fragment() should check CHECKSUM_PARTIAL")
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Vlad Yasevich <vyasevich@...il.com>
> Cc: Benjamin Coddington <bcodding@...hat.com>
> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
> ---
>  net/ipv6/ip6_output.c | 78 ++++++++++++++++++++++++---------------------------
>  1 file changed, 37 insertions(+), 41 deletions(-)
> 
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 8dddb45..26d2911 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -593,6 +593,10 @@ int ip6_fragment(struct sock *sk, struct sk_buff *skb,
>  	frag_id = ipv6_select_ident(net, &ipv6_hdr(skb)->daddr,
>  				    &ipv6_hdr(skb)->saddr);
>  
> +	if ((skb->ip_summed == CHECKSUM_PARTIAL) &&
> +	    (err = skb_checksum_help(skb)))
> +		goto fail;
> +
>  	hroom = LL_RESERVED_SPACE(rt->dst.dev);
>  	if (skb_has_frag_list(skb)) {
>  		int first_len = skb_pagelen(skb);
> @@ -721,10 +725,6 @@ slow_path_clean:
>  	}
>  
>  slow_path:
> -	if ((skb->ip_summed == CHECKSUM_PARTIAL) &&
> -	    skb_checksum_help(skb))
> -		goto fail;
> -


It looks like this patch could be split in two, to ease future bisection
maybe ?



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