netdev - Re: [PATCH 2/2] vti6: do not check for ignore

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Date:   Fri, 31 Aug 2018 08:42:32 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
CC:     <netdev@...r.kernel.org>, <yoshfuji@...ux-ipv6.org>,
        <kuznet@....inr.ac.ru>, <davem@...emloft.net>,
        <herbert@...dor.apana.org.au>, <eyal.birger@...il.com>
Subject: Re: [PATCH 2/2] vti6: do not check for ignore_df in order to update
 pmtu

On Thu, Aug 30, 2018 at 09:58:17AM -0300, Thadeu Lima de Souza Cascardo wrote:
> Before commit d6990976af7c5d8f55903bfb4289b6fb030bf754 ("vti6: fix PMTU caching
> and reporting on xmit"), skb was scrubbed before checking for ignore_df. The
> scrubbing meant ignore_df was false, making the check irrelevant. Now that the
> scrubbing happens after that, some packets might fail the checking and dst
> will not have its pmtu updated.
> 
> Not only that, but too big skb will be potentially passed down to
> __xfrm6_output, causing it to fail to transmit but not free the skb, causing a
> leak of skb, and consequentially a leak of dst references.
> 
> After running pmtu.sh, that shows as failure to unregister devices in a namespace:
> 
> [  311.397671] unregister_netdevice: waiting for veth_b to become free. Usage count = 1
> 
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
> ---
>  net/ipv6/ip6_vti.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
> index c72ae3a4fe09..fbd3752ea587 100644
> --- a/net/ipv6/ip6_vti.c
> +++ b/net/ipv6/ip6_vti.c
> @@ -481,7 +481,7 @@ vti6_xmit(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
>  	}
>  
>  	mtu = dst_mtu(dst);
> -	if (!skb->ignore_df && skb->len > mtu) {
> +	if (skb->len > mtu) {
>  		skb_dst_update_pmtu(skb, mtu);

The very same patch went already to the net tree two day ago:

commit 9f2895461439fda2801a7906fb4c5fb3dbb37a0a
vti6: remove !skb->ignore_df check from vti6_xmit()