From: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Date: Wed, 30 Dec 2015 08:51:12 -0500
> From: Eric Dumazet <edumazet@xxxxxxxxxx>
>
> Backport of this upstream commit into stable kernels :
> 89c22d8c3b27 ("net: Fix skb csum races when peeking")
> exposed a bug in udp stack vs MSG_PEEK support, when user provides
> a buffer smaller than skb payload.
>
> In this case,
> skb_copy_and_csum_datagram_iovec(skb, sizeof(struct udphdr),
> msg->msg_iov);
> returns -EFAULT.
>
> This bug does not happen in upstream kernels since Al Viro did a great
> job to replace this into :
> skb_copy_and_csum_datagram_msg(skb, sizeof(struct udphdr), msg);
> This variant is safe vs short buffers.
>
> For the time being, instead reverting Herbert Xu patch and add back
> skb->ip_summed invalid changes, simply store the result of
> udp_lib_checksum_complete() so that we avoid computing the checksum a
> second time, and avoid the problematic
> skb_copy_and_csum_datagram_iovec() call.
>
> This patch can be applied on recent kernels as it avoids a double
> checksumming, then backported to stable kernels as a bug fix.
>
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Applied, thanks Eric.
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