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
> ---
> 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()
