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Maciej Żenczykowski ba05057bd0 net/ipv4: always honour route mtu during forwarding 
[ Upstream commit 02a1b175b0 ]

Documentation/networking/ip-sysctl.txt:46 says:
  ip_forward_use_pmtu - BOOLEAN
    By default we don't trust protocol path MTUs while forwarding
    because they could be easily forged and can lead to unwanted
    fragmentation by the router.
    You only need to enable this if you have user-space software
    which tries to discover path mtus by itself and depends on the
    kernel honoring this information. This is normally not the case.
    Default: 0 (disabled)
    Possible values:
    0 - disabled
    1 - enabled

Which makes it pretty clear that setting it to 1 is a potential
security/safety/DoS issue, and yet it is entirely reasonable to want
forwarded traffic to honour explicitly administrator configured
route mtus (instead of defaulting to device mtu).

Indeed, I can't think of a single reason why you wouldn't want to.
Since you configured a route mtu you probably know better...

It is pretty common to have a higher device mtu to allow receiving
large (jumbo) frames, while having some routes via that interface
(potentially including the default route to the internet) specify
a lower mtu.

Note that ipv6 forwarding uses device mtu unless the route is locked
(in which case it will use the route mtu).

This approach is not usable for IPv4 where an 'mtu lock' on a route
also has the side effect of disabling TCP path mtu discovery via
disabling the IPv4 DF (don't frag) bit on all outgoing frames.

I'm not aware of a way to lock a route from an IPv6 RA, so that also
potentially seems wrong.

Signed-off-by: Maciej Żenczykowski <maze@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Lorenzo Colitti <lorenzo@google.com>
Cc: Sunmeet Gill (Sunny) <sgill@quicinc.com>
Cc: Vinay Paradkar <vparadka@qti.qualcomm.com>
Cc: Tyler Wear <twear@quicinc.com>
Cc: David Ahern <dsahern@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2020-10-29 09:57:24 +01:00
..
9p treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 188 2019-05-30 11:29:21 -07:00
bluetooth Bluetooth: Disconnect if E0 is used for Level 4 2020-10-17 10:11:22 +02:00
caif treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 194 2019-05-30 11:29:22 -07:00
iucv net/af_iucv: locate IUCV header via skb_network_header() 2018-09-26 09:56:07 -07:00
netfilter netfilter: nf_tables: fix destination register zeroing 2020-09-09 19:12:24 +02:00
netns netfilter: nf_tables: autoload modules from the abort path 2020-01-29 16:45:33 +01:00
nfc treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 234 2019-06-19 17:09:07 +02:00
phonet treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 336 2019-06-05 17:37:07 +02:00
sctp net: sctp: Fix IPv6 ancestor_size calc in sctp_copy_descendant 2020-09-26 18:03:13 +02:00
tc_act net: sched: take reference to psample group in flow_action infra 2019-09-16 09:18:03 +02:00
6lowpan.h
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Space.h
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act_api.h net_sched: defer tcf_idr_insert() in tcf_action_init_1() 2020-10-14 10:33:06 +02:00
addrconf.h ipv6: fix memory leaks on IPV6_ADDRFORM path 2020-08-11 15:33:39 +02:00
af_ieee802154.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 174 2019-05-30 11:26:41 -07:00
af_rxrpc.h rxrpc: Make rxrpc_kernel_get_srtt() indicate validity 2020-09-09 19:12:23 +02:00
af_unix.h net: split out functions related to registering inflight socket files 2019-02-28 08:24:23 -07:00
af_vsock.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 321 2019-06-05 17:37:05 +02:00
ah.h
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arp.h net: avoid potential false sharing in neighbor related code 2019-12-31 16:45:03 +01:00
atmclip.h
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ax25.h ax25: fix possible use-after-free 2019-01-23 11:18:00 -08:00
ax88796.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
bond_3ad.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 90 2019-05-24 17:37:53 +02:00
bond_alb.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 5 2019-05-21 11:28:40 +02:00
bond_options.h bonding: add an option to specify a delay between peer notifications 2019-07-04 12:30:48 -07:00
bonding.h bonding: fix state transition issue in link monitoring 2019-11-05 17:40:16 -08:00
bpf_sk_storage.h bpf: support cloning sk storage on accept() 2019-08-17 23:18:54 +02:00
busy_poll.h net: annotate lockless accesses to sk->sk_napi_id 2019-10-30 17:34:35 -07:00
calipso.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 13 2019-05-21 11:28:45 +02:00
cfg80211-wext.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
cfg80211.h cfg80211: Fix radar event during another phy CAC 2020-02-05 21:22:46 +00:00
cfg802154.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 174 2019-05-30 11:26:41 -07:00
checksum.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
cipso_ipv4.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 13 2019-05-21 11:28:45 +02:00
cls_cgroup.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
codel.h
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codel_impl.h
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codel_qdisc.h
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compat.h net: rework SIOCGSTAMP ioctl handling 2019-04-19 14:07:40 -07:00
datalink.h
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dcbevent.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 201 2019-05-30 11:29:52 -07:00
dcbnl.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 201 2019-05-30 11:29:52 -07:00
devlink.h devlink: disallow reload operation during device cleanup 2019-11-09 19:38:36 -08:00
dn.h
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dn_dev.h
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dn_fib.h
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dn_neigh.h
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dn_nsp.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 24 2019-05-21 11:52:39 +02:00
dn_route.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 24 2019-05-21 11:52:39 +02:00
drop_monitor.h net: drop_monitor: use IS_REACHABLE() to guard net_dm_hw_report() 2020-05-27 17:46:24 +02:00
dsa.h net: dsa: Pass ndo_setup_tc slave callback to drivers 2019-09-16 21:32:57 +02:00
dsfield.h
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dst.h net: Added pointer check for dst->ops->neigh_lookup in dst_neigh_lookup_skb 2020-07-22 09:32:47 +02:00
dst_cache.h
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dst_metadata.h
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dst_ops.h net: add bool confirm_neigh parameter for dst_ops.update_pmtu 2020-01-04 19:18:58 +01:00
erspan.h erspan: set bso bit based on mirrored packet's len 2018-05-20 18:31:42 -04:00
esp.h
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ethoc.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
failover.h net: Introduce generic failover module 2018-05-28 22:59:54 -04:00
fib_notifier.h net: fib: drop include of module.h from fib_notifier.h 2019-04-22 21:50:53 -07:00
fib_rules.h fib: add missing attribute validation for tun_id 2020-03-18 07:17:44 +01:00
firewire.h
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flow.h ipv4: Initialize flowi4_multipath_hash in data path 2020-09-26 18:03:12 +02:00
flow_dissector.h net: sched: correct flower port blocking 2020-03-05 16:43:32 +01:00
flow_offload.h net: core: rename indirect block ingress cb function 2019-12-18 16:08:47 +01:00
fou.h
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fq.h net/flow_dissector: switch to siphash 2019-10-23 20:13:22 -07:00
fq_impl.h net/fq_impl: Switch to kvmalloc() for memory allocation 2019-11-08 09:11:49 +01:00
garp.h
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gen_stats.h net: align gnet_stats_basic_cpu struct 2018-11-17 21:37:29 -08:00
genetlink.h genetlink: remove genl_bind 2020-07-22 09:32:46 +02:00
geneve.h net: Move the definition of the default Geneve udp port to public header file 2019-03-22 12:09:31 -07:00
gre.h net: Add netif_is_gretap()/netif_is_ip6gretap() 2018-12-10 15:53:04 -08:00
gro_cells.h
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gtp.h
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gue.h net:gue.h:Fix shifting signed 32-bit value by 31 bits problem 2019-07-01 10:58:23 -07:00
hwbm.h net: hwbm: if CONFIG_NET_HWBM unset, make stub functions static 2019-10-25 16:24:32 -07:00
icmp.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
ieee80211_radiotap.h wireless-drivers-next patches for 5.1 2019-02-22 12:56:24 -08:00
ieee802154_netdev.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 174 2019-05-30 11:26:41 -07:00
if_inet6.h ipv6: shrink struct ipv6_mc_socklist 2019-08-28 14:43:03 -07:00
ife.h net: ife: drop include of module.h from net/ife.h 2019-04-22 21:50:53 -07:00
ila.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
inet6_connection_sock.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
inet6_hashtables.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
inet_common.h inet: factor out inet_send_prepare() 2019-07-03 13:51:54 -07:00
inet_connection_sock.h net: refactor bind_bucket fastreuse into helper 2020-08-19 08:16:23 +02:00
inet_ecn.h sched: consistently handle layer3 header accesses in the presence of VLANs 2020-07-22 09:32:48 +02:00
inet_frag.h inet: frags: re-introduce skb coalescing for local delivery 2019-08-08 15:55:10 -07:00
inet_hashtables.h dccp: Fix possible memleak in dccp_init and dccp_fini 2020-06-17 16:40:32 +02:00
inet_sock.h ip: support SO_MARK cmsg 2019-09-13 21:44:19 +02:00
inet_timewait_sock.h tcp: honor SO_PRIORITY in TIME_WAIT state 2019-09-27 12:05:02 +02:00
inetpeer.h net: ipv4: use a dedicated counter for icmp_v4 redirect packets 2019-02-08 21:50:15 -08:00
ip.h net/ipv4: always honour route mtu during forwarding 2020-10-29 09:57:24 +01:00
ip6_checksum.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
ip6_fib.h ipv6: Use global sernum for dst validation with nexthop objects 2020-05-14 07:58:20 +02:00
ip6_route.h net: ipv6: do not consider routes via gateways for anycast address check 2020-04-21 09:04:45 +02:00
ip6_tunnel.h ip6_tunnel: allow not to count pkts on tstats by passing dev as NULL 2019-06-18 20:48:45 -04:00
ip_fib.h ipv4: nexthop version of fib_info_nh_uses_dev 2020-06-03 08:21:37 +02:00
ip_tunnels.h route: Add multipath_hash in flowi_common to make user-define hash 2019-02-27 12:50:17 -08:00
ip_vs.h ipvs: allow connection reuse for unconfirmed conntrack 2020-08-19 08:16:10 +02:00
ipcomp.h
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ipconfig.h
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ipv6.h net: ipv6: add net argument to ip6_dst_lookup_flow 2019-12-18 16:08:40 +01:00
ipv6_frag.h inet: fix various use-after-free in defrags units 2019-06-19 11:37:47 -04:00
ipv6_stubs.h net: ipv6_stub: use ip6_dst_lookup_flow instead of ip6_dst_lookup 2019-12-18 16:08:42 +01:00
ipx.h bonding/alb: properly access headers in bond_alb_xmit() 2020-02-11 04:35:48 -08:00
iw_handler.h
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kcm.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
l3mdev.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
lag.h net: Add lag.h, net_lag_port_dev_txable() 2018-07-11 23:10:19 -07:00
lapb.h
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lib80211.h
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llc.h llc: avoid blocking in llc_sap_close() 2018-09-13 09:04:58 -07:00
llc_c_ac.h
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llc_c_ev.h
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llc_c_st.h
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llc_conn.h llc: fix sk_buff leak in llc_conn_service() 2019-10-08 13:23:05 -07:00
llc_if.h
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llc_pdu.h
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llc_s_ac.h
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llc_s_ev.h
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llc_s_st.h
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llc_sap.h
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lwtunnel.h lwtunnel: Pass encap and encap type attributes to lwtunnel_fill_encap 2019-04-23 19:42:29 -07:00
mac80211.h mac80211: populate debugfs only after cfg80211 init 2020-04-29 16:33:18 +02:00
mac802154.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 174 2019-05-30 11:26:41 -07:00
mip6.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 13 2019-05-21 11:28:45 +02:00
mld.h
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mpls.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 295 2019-06-05 17:36:38 +02:00
mpls_iptunnel.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 295 2019-06-05 17:36:38 +02:00
mrp.h
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ncsi.h
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ndisc.h net: avoid potential false sharing in neighbor related code 2019-12-31 16:45:03 +01:00
neighbour.h net: add annotations on hh->hh_len lockless accesses 2020-01-09 10:20:06 +01:00
net_failover.h net: Introduce net_failover driver 2018-05-28 22:59:54 -04:00
net_namespace.h ipv6: Use global sernum for dst validation with nexthop objects 2020-05-14 07:58:20 +02:00
net_ratelimit.h
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netevent.h net: ipv4: Notify about changes to ip_forward_update_priority 2018-08-01 09:52:30 -07:00
netlabel.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 13 2019-05-21 11:28:45 +02:00
netlink.h netlink: Fix nlmsg_parse as a wrapper for strict message parsing 2019-08-13 20:37:16 -07:00
netprio_cgroup.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
netrom.h net: netrom: Fix error cleanup path of nr_proto_init 2019-04-11 13:59:49 -07:00
nexthop.h ipv4: nexthop version of fib_info_nh_uses_dev 2020-06-03 08:21:37 +02:00
nl802154.h
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nsh.h
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p8022.h
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page_pool.h page_pool: do not release pool until inflight == 0. 2019-12-18 16:09:07 +01:00
ping.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
pkt_cls.h net_sched: fix ops->bind_class() implementations 2020-02-01 09:34:38 +00:00
pkt_sched.h sched: consistently handle layer3 header accesses in the presence of VLANs 2020-07-22 09:32:48 +02:00
pptp.h
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protocol.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
psample.h net: sched: take reference to psample group in flow_action infra 2019-09-16 09:18:03 +02:00
psnap.h
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raw.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
rawv6.h
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red.h
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regulatory.h cfg80211: make wmm_rule part of the reg_rule structure 2018-08-28 11:11:47 +02:00
request_sock.h net: add {READ|WRITE}_ONCE() annotations on ->rskq_accept_head 2019-10-09 21:34:31 -07:00
rose.h proc: introduce proc_create_seq{,_data} 2018-05-16 07:23:35 +02:00
route.h ipv4: Revert removal of rt_uses_gateway 2019-09-20 18:23:33 -07:00
rsi_91x.h
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rtnetlink.h net: Add extack argument to rtnl_create_link 2018-11-06 15:00:45 -08:00
rtnh.h net: Rename net/nexthop.h net/rtnh.h 2019-04-22 21:47:25 -07:00
sch_generic.h net_sched: fix tcm_parent in tc filter dump 2020-05-20 08:20:07 +02:00
scm.h pids: Compute task_tgid using signal->leader_pid 2018-07-21 10:43:12 -05:00
secure_seq.h
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seg6.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
seg6_hmac.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
seg6_local.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
slhc_vj.h slip: Check if rstate is initialized before uncompressing 2018-04-11 10:33:46 -04:00
smc.h net/smc: add smcd support to the pnet table 2019-02-21 10:34:37 -08:00
snmp.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
sock.h net: silence data-races on sk_backlog.tail 2020-10-01 13:17:15 +02:00
sock_reuseport.h udp: correct reuseport selection with connected sockets 2019-09-16 09:02:18 +02:00
stp.h
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strparser.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
switchdev.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
tcp.h tcp: correct read of TFO keys on big endian systems 2020-08-19 08:16:23 +02:00
tcp_states.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
timewait_sock.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
tipc.h flow_dissector: do not rely on implicit casts 2018-05-08 00:02:41 -04:00
tls.h bpf: Fix running sk_skb program types with ktls 2020-06-22 09:31:12 +02:00
transp_v6.h ipv6: fold sockcm_cookie into ipcm6_cookie 2018-07-07 10:58:49 +09:00
tso.h
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tun_proto.h
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udp.h udp: document udp_rcv_segment special case for looped packets 2020-05-10 10:31:33 +02:00
udp_tunnel.h ipv6: Move ipv6 stubs to a separate header file 2019-03-29 10:53:45 -07:00
udplite.h
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vsock_addr.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 321 2019-06-05 17:37:05 +02:00
vxlan.h vxlan: add adjacent link to limit depth level 2019-10-24 14:53:49 -07:00
wext.h
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wimax.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 268 2019-06-05 17:30:29 +02:00
x25.h
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x25device.h
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xdp.h xdp: page_pool related fix to cpumap 2019-06-19 11:23:13 -04:00
xdp_priv.h page_pool: do not release pool until inflight == 0. 2019-12-18 16:09:07 +01:00
xdp_sock.h xsk: add support to allow unaligned chunk placement 2019-08-31 01:08:26 +02:00
xfrm.h xfrm: clone XFRMA_REPLAY_ESN_VAL in xfrm_do_migrate 2020-10-14 10:33:02 +02:00