From: Florian Westphal <fw@strlen.de>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Praveen Chaudhary <praveen5582@gmail.com>,
fw@strlen.de, pablo@netfilter.org, davem@davemloft.net,
kadlec@netfilter.org, netfilter-devel@vger.kernel.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Zhenggen Xu <zxu@linkedin.com>,
Andy Stracner <astracner@linkedin.com>
Subject: Re: [PATCH v3] [net]: Fix skb->csum update in inet_proto_csum_replace16().
Date: Wed, 22 Jan 2020 12:43:33 +0100 [thread overview]
Message-ID: <20200122114333.GQ795@breakpoint.cc> (raw)
In-Reply-To: <16d56ee6-53bc-1124-3700-bc0a78f927d6@iogearbox.net>
Daniel Borkmann <daniel@iogearbox.net> wrote:
> > @@ -449,9 +464,6 @@ void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb,
> > if (skb->ip_summed != CHECKSUM_PARTIAL) {
> > *sum = csum_fold(csum_partial(diff, sizeof(diff),
> > ~csum_unfold(*sum)));
> > - if (skb->ip_summed == CHECKSUM_COMPLETE && pseudohdr)
> > - skb->csum = ~csum_partial(diff, sizeof(diff),
> > - ~skb->csum);
>
> What is the technical rationale in removing this here but not in any of the
> other inet_proto_csum_replace*() functions? You changelog has zero analysis
> on why here but not elsewhere this change would be needed?
Right, I think it could be dropped everywhere BUT there is a major caveat:
At least for the nf_nat case ipv4 header manipulation (which uses the other
helpers froum utils.c) will eventually also update iph->checksum field
to account for the changed ip addresses.
And that update doesn't touch skb->csum.
So in a way the update of skb->csum in the other helpers indirectly account
for later ip header checksum update.
At least that was my conclusion when reviewing the earlier incarnation
of the patch.
next prev parent reply other threads:[~2020-01-22 11:43 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-06 22:52 [PATCH v3] [net]: Fix skb->csum update in inet_proto_csum_replace16() Praveen Chaudhary
2019-11-06 22:52 ` Praveen Chaudhary
2020-01-22 10:17 ` Daniel Borkmann
2020-01-22 11:43 ` Florian Westphal [this message]
2020-01-22 16:22 ` Daniel Borkmann
2020-01-23 8:21 ` Florian Westphal
2020-01-23 14:20 ` Daniel Borkmann
2020-01-23 14:29 ` Florian Westphal
2020-01-23 20:33 ` [PATCH v4] " Praveen Chaudhary
2020-01-23 20:33 ` Praveen Chaudhary
2020-01-24 19:04 ` Pablo Neira Ayuso
2020-01-23 20:50 ` [PATCH v3] " Praveen Chaudhary
2020-01-22 5:51 ` Praveen Chaudhary
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