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

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Date:	Thu, 31 Dec 2015 06:39:44 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Michal Kubecek <mkubecek@...e.cz>,
	David Miller <davem@...emloft.net>,
	Sabrina Dubroca <sd@...asysnail.net>, stable@...r.kernel.org,
	Jiri Slaby <jslaby@...e.cz>,
	Ben Hutchings <ben@...adent.org.uk>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] udp: properly support MSG_PEEK with truncated
 buffers

On Wed, Dec 30, 2015 at 08:51:12AM -0500, Eric Dumazet wrote:
> 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>

Acked-by: Herbert Xu <herbert@...dor.apana.org.au>
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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