kernel/linux.git/include/net/ip6_route.h, branch linux-7.2.y

net: advertise TCP MSS from the configured MTU, not the learned PMTU

2026-09-02T12:33:19+00:00

commit 2640e64195948a601430d230c9864f5426574cde upstream. The MSS a host puts in its SYN tells the peer how big a segment it may send us. Right now we can shrink it with a PMTU we learned on our own send path, which is the wrong direction entirely. On asymmetric paths this bites - think DSR load balancers, where the request side goes through a smaller-MTU overlay. We learn a small PMTU going out, then advertise a small MSS, and the peer stays capped for the whole connection even though its path back to us is wide. MSS only shows up in the SYN and never grows back. On symmetric paths we lose nothing by dropping it either: the peer runs its own PMTU discovery and usually already knows the real path MTU. So work out the advertised MSS from the configured route or device MTU and ignore the learned PMTU. Our send side is unchanged, still clamped by tcp_current_mss(). Add ip_dst_mtu_configured()/ip6_dst_mtu_configured() and use them from the two default_advmss() paths. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Fixes: 164a5e7ad531 ("ipv4: ipv4_default_advmss() should use route mtu") Cc: stable@vger.kernel.org Signed-off-by: Jiayuan Chen Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260815070413.294559-1-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman

ipv6: prepare headers for ipv6_stub removal

2026-03-29T18:21:23+00:00

In preparation for dropping ipv6_stub and converting its users to direct function calls, introduce static inline dummy functions and fallback macros in the IPv6 networking headers. In addition, introduce checks on fib6_nh_init(), ip6_dst_lookup_flow() and ip6_fragment() to avoid a crash due to ipv6.disable=1 set during booting. The other functions are safe as they cannot be called with ipv6.disable=1 set. These fallbacks ensure that when CONFIG_IPV6 is completely disabled, there are no compiling or linking errors due to code paths not guarded by preprocessor macro IS_ENABLED(CONFIG_IPV6). In addition, export ndisc_send_na(), ip6_route_input() and ip6_fragment(). Signed-off-by: Fernando Fernandez Mancera Tested-by: Ricardo B. Marlière Link: https://patch.msgid.link/20260325120928.15848-6-fmancera@suse.de Signed-off-by: Jakub Kicinski

ipv6: make ipv6_anycast_destination logic usable without dst_entry

2026-03-04T10:45:44+00:00

nft_fib_ipv6 uses ipv6_anycast_destination(), but upcoming patch removes the dst_entry usage in favor of fib6_result. Move the 'plen > 127' logic to a new helper and call it from the existing one. Signed-off-by: Florian Westphal

inet: add dst4_mtu() and dst6_mtu() helpers

2026-02-03T01:49:29+00:00

With CONFIG_MITIGATION_RETPOLINE=y dst_mtu() is a bit fat, because it is generic. Indeed, clang does not always inline it. Add dst4_mtu() and dst6_mtu() helpers for callers that expect either ipv4_mtu() or ip6_mtu() to be called. These helpers are always inlined. Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20260130210303.3888261-6-edumazet@google.com Signed-off-by: Jakub Kicinski

ipv6: make ipv6_pinfo.daddr_cache a boolean

2025-09-18T08:17:09+00:00

ipv6_pinfo.daddr_cache is either NULL or &sk->sk_v6_daddr We do not need 8 bytes, a boolean is enough. Signed-off-by: Eric Dumazet Reviewed-by: Willem de Bruijn Reviewed-by: David Ahern Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20250916160951.541279-3-edumazet@google.com Reviewed-by: Jakub Kicinski Signed-off-by: Paolo Abeni

ipv6: make ipv6_pinfo.saddr_cache a boolean

2025-09-18T08:17:09+00:00

ipv6_pinfo.saddr_cache is either NULL or &np->saddr. We do not need 8 bytes, a boolean is enough. Signed-off-by: Eric Dumazet Reviewed-by: Willem de Bruijn Reviewed-by: David Ahern Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20250916160951.541279-2-edumazet@google.com Reviewed-by: Jakub Kicinski Signed-off-by: Paolo Abeni

net: use dst_dev_rcu() in sk_setup_caps()

2025-08-30T02:36:32+00:00

Use RCU to protect accesses to dst->dev from sk_setup_caps() and sk_dst_gso_max_size(). Also use dst_dev_rcu() in ip6_dst_mtu_maybe_forward(), and ip_dst_mtu_maybe_forward(). ip4_dst_hoplimit() can use dst_dev_net_rcu(). Fixes: 4a6ce2b6f2ec ("net: introduce a new function dst_dev_put()") Signed-off-by: Eric Dumazet Reviewed-by: David Ahern Link: https://patch.msgid.link/20250828195823.3958522-6-edumazet@google.com Signed-off-by: Jakub Kicinski

ipv6: adopt dst_dev() helper

2025-07-02T21:32:30+00:00

Use the new helper as a step to deal with potential dst->dev races. Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20250630121934.3399505-9-edumazet@google.com Signed-off-by: Jakub Kicinski

ipv6: fix source address selection with route leak

2024-07-14T14:34:16+00:00

By default, an address assigned to the output interface is selected when the source address is not specified. This is problematic when a route, configured in a vrf, uses an interface from another vrf (aka route leak). The original vrf does not own the selected source address. Let's add a check against the output interface and call the appropriate function to select the source address. CC: stable@vger.kernel.org Fixes: 0d240e7811c4 ("net: vrf: Implement get_saddr for IPv6") Signed-off-by: Nicolas Dichtel Link: https://patch.msgid.link/20240710081521.3809742-3-nicolas.dichtel@6wind.com Signed-off-by: Jakub Kicinski

ipv6: introduce dst_rt6_info() helper

2024-04-29T12:32:01+00:00

Instead of (struct rt6_info *)dst casts, we can use : #define dst_rt6_info(_ptr) \ container_of_const(_ptr, struct rt6_info, dst) Some places needed missing const qualifiers : ip6_confirm_neigh(), ipv6_anycast_destination(), ipv6_unicast_destination(), has_gateway() v2: added missing parts (David Ahern) Signed-off-by: Eric Dumazet Reviewed-by: David Ahern Signed-off-by: David S. Miller