linux-kernel - Re: [PATCH v4] [net]: Fix skb->csum update in inet_proto_csum

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Message-ID: <20200124190432.vxcnnds3ypqa4hzh@salvia>
Date:   Fri, 24 Jan 2020 20:04:32 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Praveen Chaudhary <praveen5582@...il.com>
Cc:     fw@...len.de, davem@...emloft.net, kadlec@...filter.org,
        netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Zhenggen Xu <zxu@...kedin.com>,
        Andy Stracner <astracner@...kedin.com>
Subject: Re: [PATCH v4] [net]: Fix skb->csum update in
 inet_proto_csum_replace16().

On Thu, Jan 23, 2020 at 12:33:28PM -0800, Praveen Chaudhary wrote:
> skb->csum is updated incorrectly, when manipulation for NF_NAT_MANIP_SRC\DST
> is done on IPV6 packet.
> 
> Fix:
> There is no need to update skb->csum in inet_proto_csum_replace16(), because
> update in two fields a.) IPv6 src/dst address and b.) L4 header checksum
> cancels each other for skb->csum calculation.
> Whereas inet_proto_csum_replace4 function needs to update skb->csum,
> because update in 3 fields a.) IPv4 src/dst address, b.) IPv4 Header checksum
> and c.) L4 header checksum results in same diff as L4 Header checksum for
> skb->csum calculation.

Applied, thanks.