4.14-stable review patch. If anyone has any objections, please let me know.
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From: Stefano Brivio sbrivio@redhat.com
[ Upstream commit dd1df24737727e119c263acf1be2a92763938297 ]
This re-introduces the effect of commit a32452366b72 ("vti4: Don't count header length twice.") which was accidentally reverted by merge commit f895f0cfbb77 ("Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec").
The commit message from Steffen Klassert said:
We currently count the size of LL_MAX_HEADER and struct iphdr twice for vti4 devices, this leads to a wrong device mtu. The size of LL_MAX_HEADER and struct iphdr is already counted in ip_tunnel_bind_dev(), so don't do it again in vti_tunnel_init().
And this is still the case now: ip_tunnel_bind_dev() already accounts for the header length of the link layer (not necessarily LL_MAX_HEADER, if the output device is found), plus one IP header.
For example, with a vti device on top of veth, with MTU of 1500, the existing implementation would set the initial vti MTU to 1332, accounting once for LL_MAX_HEADER (128, included in hard_header_len by vti) and twice for the same IP header (once from hard_header_len, once from ip_tunnel_bind_dev()).
It should instead be 1480, because ip_tunnel_bind_dev() is able to figure out that the output device is veth, so no additional link layer header is attached, and will properly count one single IP header.
The existing issue had the side effect of avoiding PMTUD for most xfrm policies, by arbitrarily lowering the initial MTU. However, the only way to get a consistent PMTU value is to let the xfrm PMTU discovery do its course, and commit d6af1a31cc72 ("vti: Add pmtu handling to vti_xmit.") now takes care of local delivery cases where the application ignores local socket notifications.
Fixes: b9959fd3b0fa ("vti: switch to new ip tunnel code") Fixes: f895f0cfbb77 ("Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec") Signed-off-by: Stefano Brivio sbrivio@redhat.com Acked-by: Sabrina Dubroca sd@queasysnail.net Signed-off-by: Steffen Klassert steffen.klassert@secunet.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/ip_vti.c | 1 - 1 file changed, 1 deletion(-)
--- a/net/ipv4/ip_vti.c +++ b/net/ipv4/ip_vti.c @@ -396,7 +396,6 @@ static int vti_tunnel_init(struct net_de memcpy(dev->dev_addr, &iph->saddr, 4); memcpy(dev->broadcast, &iph->daddr, 4);
- dev->hard_header_len = LL_MAX_HEADER + sizeof(struct iphdr); dev->mtu = ETH_DATA_LEN; dev->flags = IFF_NOARP; dev->addr_len = 4;