netdev - Re: [PATCH net-next] udp: properly support MSG

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Message-Id: <20160104.172513.383473031591056204.davem@davemloft.net>
Date:	Mon, 04 Jan 2016 17:25:13 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	mkubecek@...e.cz, sd@...asysnail.net, stable@...r.kernel.org,
	jslaby@...e.cz, ben@...adent.org.uk, netdev@...r.kernel.org,
	herbert@...dor.apana.org.au
Subject: Re: [PATCH net-next] udp: properly support MSG_PEEK with truncated
 buffers

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 30 Dec 2015 08:51:12 -0500

> From: Eric Dumazet <edumazet@...gle.com>
> 
> 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@...gle.com>

Applied, thanks Eric.
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