On 6/24/20 4:48 AM, Oliver Herms wrote:
> The calculation of the effective tunnel mtu, that is used to create
> mtu exceptions if necessary, is currently not done correctly. This
> leads to unnecessary entries in the IPv6 route cache for any packet
> to be sent through the tunnel.
>
> The root cause is, that "dev->hard_header_len" is subtracted from the
> tunnel destinations path mtu. Thus subtracting too much, if
> dev->hard_header_len is filled in. This is that case for SIT tunnels
> where hard_header_len is the underlyings dev's hard_header_len (e.g. 14
> for ethernet) + 20 bytes IP header (see net/ipv6/sit.c:1091).
>
> However, the MTU of the path is exclusive of the ethernet header
> and the 20 bytes for the IP header are being subtracted separately
> already. Thus hard_header_len is removed from this calculation.
>
> For IPIP and GRE tunnels this doesn't change anything as hard_header_len
> is zero in those cases anyways.
>
> Signed-off-by: Oliver Herms <oliver.peter.he...@gmail.com>
> ---
> net/ipv4/ip_tunnel.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
> index f4f1d11eab50..871d28bd29fa 100644
> --- a/net/ipv4/ip_tunnel.c
> +++ b/net/ipv4/ip_tunnel.c
> @@ -495,8 +495,7 @@ static int tnl_update_pmtu(struct net_device *dev, struct
> sk_buff *skb,
> pkt_size = skb->len - tunnel_hlen - dev->hard_header_len;
>
> if (df)
> - mtu = dst_mtu(&rt->dst) - dev->hard_header_len
> - - sizeof(struct iphdr) - tunnel_hlen;
> + mtu = dst_mtu(&rt->dst) - sizeof(struct iphdr) - tunnel_hlen;
> else
> mtu = skb_valid_dst(skb) ? dst_mtu(skb_dst(skb)) : dev->mtu;
>
>
Can you add a Fixes: tag, to help stable teams work ?
Thanks.
