On Mon, 2015-07-13 at 20:01 +0800, Herbert Xu wrote:
> ---8<---
> When we calculate the checksum on the recv path, we store the
> result in the skb as an optimisation in case we need the checksum
> again down the line.
>
> This is in fact bogus for the MSG_PEEK case as this is done without
> any locking. So multiple threads can peek and then store the result
> to the same skb, potentially resulting in bogus skb states.
>
> This patch fixes this by only storing the result if the skb is not
> shared. This preserves the optimisations for the few cases where
> it can be done safely due to locking or other reasons, e.g., SIOCINQ.
>
> Signed-off-by: Herbert Xu <herb...@gondor.apana.org.au>
>
> diff --git a/net/core/datagram.c b/net/core/datagram.c
> index b80fb91..4967262 100644
> --- a/net/core/datagram.c
> +++ b/net/core/datagram.c
> @@ -622,7 +657,8 @@ __sum16 __skb_checksum_complete_head(struct sk_buff *skb,
> int len)
> !skb->csum_complete_sw)
> netdev_rx_csum_fault(skb->dev);
> }
> - skb->csum_valid = !sum;
> + if (!skb_shared(skb))
> + skb->csum_valid = !sum;
> return sum;
> }
> EXPORT_SYMBOL(__skb_checksum_complete_head);
> @@ -642,11 +678,13 @@ __sum16 __skb_checksum_complete(struct sk_buff *skb)
> netdev_rx_csum_fault(skb->dev);
> }
>
> - /* Save full packet checksum */
> - skb->csum = csum;
> - skb->ip_summed = CHECKSUM_COMPLETE;
> - skb->csum_complete_sw = 1;
> - skb->csum_valid = !sum;
> + if (!skb_shared(skb)) {
> + /* Save full packet checksum */
> + skb->csum = csum;
> + skb->ip_summed = CHECKSUM_COMPLETE;
> + skb->csum_complete_sw = 1;
> + skb->csum_valid = !sum;
> + }
>
> return sum;
> }
Acked-by: Eric Dumazet <eduma...@google.com>
Thanks !
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