netdev - Re: [PATCH net] skbuff: Fix skb checksum partial check.

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Date:	Mon, 28 Sep 2015 17:46:50 -0700
From:	Tom Herbert <tom@...bertland.com>
To:	Pravin B Shelar <pshelar@...ira.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net] skbuff: Fix skb checksum partial check.

On Mon, Sep 28, 2015 at 5:24 PM, Pravin B Shelar <pshelar@...ira.com> wrote:
> Earlier patch 6ae459bda tried to detect void ckecksum partial
> skb by comparing pull length to checksum offset. But it does
> not work for all cases since checksum-offset depends on
> updates to skb->data.
>
> Following patch fixes it by validating checksum start offset
> after skb-data pointer is updated. Negative value of checksum
> offset start means there is no need to checksum.
>
> Fixes: 6ae459bda ("skbuff: Fix skb checksum flag on skb pull")
> Reported-by: Andrew Vagin <avagin@...n.com>
> Signed-off-by: Pravin B Shelar <pshelar@...ira.com>
> ---
> This and 6ae459bda patches needs to be backported to stable.
> ---
>  include/linux/skbuff.h |    2 +-
>  net/core/skbuff.c      |    9 +++++----
>  2 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 2b0a30a..4398411 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -2708,7 +2708,7 @@ static inline void skb_postpull_rcsum(struct sk_buff *skb,
>         if (skb->ip_summed == CHECKSUM_COMPLETE)
>                 skb->csum = csum_sub(skb->csum, csum_partial(start, len, 0));
>         else if (skb->ip_summed == CHECKSUM_PARTIAL &&
> -                skb_checksum_start_offset(skb) <= len)
> +                skb_checksum_start_offset(skb) < 0)
>                 skb->ip_summed = CHECKSUM_NONE;
>  }
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index dad4dd3..fab4599 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -2958,11 +2958,12 @@ EXPORT_SYMBOL_GPL(skb_append_pagefrags);
>   */
>  unsigned char * skb_pull_rcsum(struct sk_buff *skb, unsigned int len)
>  {
> +       unsigned char *data = skb->data;
> +
>         BUG_ON(len > skb->len);
> -       skb->len -= len;
> -       BUG_ON(skb->len < skb->data_len);
> -       skb_postpull_rcsum(skb, skb->data, len);
> -       return skb->data += len;
> +       __skb_pull(skb, len);
> +       skb_postpull_rcsum(skb, data, len);
> +       return skb->data;
>  }

Nice cleanup in skb_pull_rcsum, but does this affect other calls to
skb_postpull_rcsum?

>  EXPORT_SYMBOL_GPL(skb_pull_rcsum);
>
> --
> 1.7.1
>
> --
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