bpf: Add MTU check to fib lookup helper

From: David Ahern <[email protected]>

Packets that exceed the egress MTU can not be forwarded in the fast path. Add IPv4 and IPv6 MTU helpers that take a FIB lookup result (versus the typical dst path) and add the calls to bpf_ipv{4,6}_fib_lookup.

v2
- add ip6_mtu_from_fib6 to ipv6_stub
- only call the new MTU helpers for fib lookups in XDP path; skb path uses is_skb_forwardable to determine if the packet can be sent via the egress device from the FIB lookup

David Ahern (3):
net/ipv4: Add helper to return path MTU based on fib result net/ipv6: Add helper to return path MTU based on fib result
bpf: Add mtu checking to FIB forwarding helper

 include/net/addrconf.h   |  2 ++
 include/net/ip6_fib.h    |  6 ++++++
 include/net/ip6_route.h  |  3 +++
 include/net/ip_fib.h     |  2 ++
 net/core/filter.c        | 42 +++++++++++++++++++++++++++++++++++-------
 net/ipv4/route.c         | 31 +++++++++++++++++++++++++++++++
 net/ipv6/addrconf_core.c |  8 ++++++++
 net/ipv6/af_inet6.c      |  1 +
 net/ipv6/route.c         | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 9 files changed, 136 insertions(+), 7 deletions(-)

2.11.0