netdev - Re: [PATCH net v2] udp: fix skb_copy_and_csum

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Date:   Thu, 4 Feb 2021 16:04:54 +0100
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, oliver.graute@...il.com,
        sagi@...mberg.me, viro@...iv.linux.org.uk, hch@....de,
        alexander.duyck@...il.com, eric.dumazet@...il.com,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net v2] udp: fix skb_copy_and_csum_datagram with odd
 segment sizes



On 2/3/21 8:29 PM, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> When iteratively computing a checksum with csum_block_add, track the
> offset "pos" to correctly rotate in csum_block_add when offset is odd.
> 
> The open coded implementation of skb_copy_and_csum_datagram did this.
> With the switch to __skb_datagram_iter calling csum_and_copy_to_iter,
> pos was reinitialized to 0 on each call.
> 
> Bring back the pos by passing it along with the csum to the callback.
> 
> Changes v1->v2
>   - pass csum value, instead of csump pointer (Alexander Duyck)
> 
> Link: https://lore.kernel.org/netdev/20210128152353.GB27281@optiplex/
> Fixes: 950fcaecd5cc ("datagram: consolidate datagram copy to iter helpers")
> Reported-by: Oliver Graute <oliver.graute@...il.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> ---
>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>