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net: lwtunnel: handle MTU calculation in forwading

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[ Upstream commit fade56410c22cacafb1be9f911a0afd3701d8366 ]

Commit 14972cbd34 ("net: lwtunnel: Handle fragmentation") moved
fragmentation logic away from lwtunnel by carry encap headroom and
use it in output MTU calculation. But the forwarding part was not
covered and created difference in MTU for output and forwarding and
further to silent drops on ipv4 forwarding path. Fix it by taking
into account lwtunnel encap headroom.

The same commit also introduced difference in how to treat RTAX_MTU
in IPv4 and IPv6 where latter explicitly removes lwtunnel encap
headroom from route MTU. Make IPv4 version do the same.

Fixes: 14972cbd34 ("net: lwtunnel: Handle fragmentation")
Suggested-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Vadim Fedorenko <vfedorenko@novek.ru>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Vadim Fedorenko
2021-06-25 19:21:39 +03:00
committed by Greg Kroah-Hartman
parent 6939c39a41
commit 4476568069
3 changed files with 22 additions and 9 deletions
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12
include/net/ip.h
View File

@@ -31,6 +31,7 @@
#include <net/flow.h>
#include <net/flow_dissector.h>
#include <net/netns/hash.h>
#include <net/lwtunnel.h>
#define IPV4_MAX_PMTU 65535U /* RFC 2675, Section 5.1 */
#define IPV4_MIN_MTU 68 /* RFC 791 */
@@ -445,22 +446,25 @@ static inline unsigned int ip_dst_mtu_maybe_forward(const struct dst_entry *dst,
/* 'forwarding = true' case should always honour route mtu */
mtu = dst_metric_raw(dst, RTAX_MTU);
if (mtu)
return mtu;
if (!mtu)
mtu = min(READ_ONCE(dst->dev->mtu), IP_MAX_MTU);
return min(READ_ONCE(dst->dev->mtu), IP_MAX_MTU);
return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
}
static inline unsigned int ip_skb_dst_mtu(struct sock *sk,
const struct sk_buff *skb)
{
unsigned int mtu;
if (!sk || !sk_fullsock(sk) || ip_sk_use_pmtu(sk)) {
bool forwarding = IPCB(skb)->flags & IPSKB_FORWARDED;
return ip_dst_mtu_maybe_forward(skb_dst(skb), forwarding);
}
return min(READ_ONCE(skb_dst(skb)->dev->mtu), IP_MAX_MTU);
mtu = min(READ_ONCE(skb_dst(skb)->dev->mtu), IP_MAX_MTU);
return mtu - lwtunnel_headroom(skb_dst(skb)->lwtstate, mtu);
}
struct dst_metrics *ip_fib_metrics_init(struct net *net, struct nlattr *fc_mx,