kernel/linux.git/include/net/ipv6.h, branch v7.2-rc1

tcp: rehash onto different local ECMP path on retransmit timeout

2026-06-15T22:57:31+00:00

Currently sk_rethink_txhash() re-rolls the socket's txhash on RTO, PLB, and spurious-retransmission events, but the cached route is reused and the new hash is not propagated into the ECMP path selection logic. Two changes are needed to make rehash select a different local ECMP path: 1. Add __sk_dst_reset() alongside sk_rethink_txhash() in tcp_write_timeout(), tcp_rcv_spurious_retrans(), and tcp_plb_check_rehash() so the cached dst is invalidated and the next transmit triggers a fresh route lookup. 2. Set fl6->mp_hash from sk_txhash (or tcp_rsk(req)->txhash for SYN/ACK retransmits and syncookies) in tcp_v6_connect(), inet6_sk_rebuild_header(), inet6_csk_route_req(), inet6_csk_route_socket(), tcp_v6_send_response(), and cookie_v6_check() so fib6_select_path() picks a path based on the new hash. The mp_hash override only applies to fib_multipath_hash_policy 0 (the default L3 policy). Its hash includes the flow label, but that is 0 by default -- np->flow_label is unset, and auto_flowlabels only computes the on-wire label later, per packet -- so flows to the same peer share one local path. Keying the hash on sk_txhash makes the local path per-connection and lets a rehash re-select it. Policies 1-3 are left unchanged. The mp_hash assignment is factored into a small helper, ip6_ecmp_set_mp_hash(), shared by inet6_csk_route_req(), inet6_csk_route_socket(), tcp_v6_connect(), inet6_sk_rebuild_header(), tcp_v6_send_response(), and cookie_v6_check(). It applies (txhash >> 1) ?: 1 for policy 0 (the >> 1 keeps mp_hash in the 31-bit range; ?: 1 keeps it non-zero, since 0 would fall back to rt6_multipath_hash()). inet6_csk_route_socket() calls it only for sk_protocol == IPPROTO_TCP so that non-TCP callers (e.g., L2TP via inet6_csk_xmit) fall through to rt6_multipath_hash() and retain their existing flow-key-based ECMP behavior. tcp_v6_send_response() also sets mp_hash from the response txhash so that a control packet (a RST from the full socket, or an ACK from a time-wait socket) selects the same local ECMP nexthop as the connection's txhash rather than falling back to the flow hash. The time-wait socket's tw_txhash is copied from sk_txhash when the connection enters TIME_WAIT, so it reflects any rehash that occurred. Setting mp_hash explicitly is necessary because the default ECMP hash derives from fl6->flowlabel via np->flow_label, which is not updated from sk_txhash (REPFLOW is off by default). ip6_make_flowlabel() cannot help either, as it runs after the route lookup. As a consequence, for policy 0 the local ECMP path of an IPv6 TCP flow follows sk_txhash even when fl6->flowlabel is non-zero, e.g. a reflected (REPFLOW) or explicitly set (IPV6_FLOWLABEL_MGR) flow label. This is intentional: only local path selection changes, so rehash can recover from a failed path; the on-wire flow label is unchanged. sk_set_txhash() is moved before ip6_dst_lookup_flow() in tcp_v6_connect() so the initial ECMP path is selected by the same txhash that subsequent route rebuilds will use. This avoids unintended path changes when the cached dst is naturally invalidated (e.g., by PMTU discovery or route changes). The rehash sites (tcp_write_timeout(), tcp_plb_check_rehash(), and tcp_rcv_spurious_retrans()) call __sk_rethink_txhash_reset_dst(), which re-rolls the txhash and, when it changed, drops the cached dst so the next transmit re-runs route selection. The dst reset is guarded by sk->sk_family == AF_INET6 since IPv4 ECMP does not currently use sk_txhash for path selection. For IPv4-mapped IPv6 sockets this produces a redundant dst reset on a cold path (RTO/PLB); the subsequent IPv4 route lookup returns the same result. The helper is deliberately separate from sk_rethink_txhash() itself: dst_negative_advice() calls sk_rethink_txhash() before its own dst op, so resetting the dst inside sk_rethink_txhash() would skip that op (e.g. rt6_remove_exception_rt()). For syncookies, cookie_init_sequence() computes the cookie value before route_req() and sets txhash so the SYN-ACK selects the same ECMP path that cookie_v6_check() will use when the full socket is created. cookie_tcp_reqsk_init() derives txhash from the cookie so the full socket's ECMP path matches the SYN-ACK. Both the SYN-ACK assignment in tcp_conn_request() and the full-socket assignment in cookie_tcp_reqsk_init() set txhash from the cookie for IPv4 and IPv6 alike. On IPv6 this drives ECMP path selection; on IPv4, which does not use sk_txhash for ECMP, it only affects TX-queue selection. That selection scales the hash by its high bits (reciprocal_scale()), which are uniform in the keyed secure_tcp_syn_cookie() output -- the MSS index only perturbs the low bits -- so the queue distribution matches net_tx_rndhash(). cookie_init_sequence() is split from the former version that also called tcp_synq_overflow() and incremented SYNCOOKIESSENT; those side effects are now in cookie_record_sent(), called after route_req() succeeds so they are not bumped when route_req() fails. cookie_record_sent() is guarded by CONFIG_SYN_COOKIES to match the guard on tcp_synq_overflow(). route_req() receives 0 as tw_isn for the syncookie path so that tcp_v6_init_req() still saves ireq->pktopts for REPFLOW flowlabel reflection and IPv6 cmsg options. The ecn_ok clear for syncookies without timestamps stays after tcp_ecn_create_request() so it takes precedence. Signed-off-by: Neil Spring Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260615042158.1600746-2-ntspring@meta.com Signed-off-by: Jakub Kicinski

ipv6: Implement limits on extension header parsing

2026-05-01T00:21:45+00:00

ipv6_{skip_exthdr,find_hdr}() and ip6_{tnl_parse_tlv_enc_lim, protocol_deliver_rcu}() iterate over IPv6 extension headers until they find a non-extension-header protocol or run out of packet data. The loops have no iteration counter, relying solely on the packet length to bound them. For a crafted packet with 8-byte extension headers filling a 64KB jumbogram, this means a worst case of up to ~8k iterations with a skb_header_pointer call each. ipv6_skip_exthdr(), for example, is used where it parses the inner quoted packet inside an incoming ICMPv6 error: - icmpv6_rcv - checksum validation - case ICMPV6_DEST_UNREACH - icmpv6_notify - pskb_may_pull() <- pull inner IPv6 header - ipv6_skip_exthdr() <- iterates here - pskb_may_pull() - ipprot->err_handler() <- sk lookup The per-iteration cost of ipv6_skip_exthdr itself is generally light, but skb_header_pointer becomes more costly on reassembled packets: the first ~1232 bytes of the inner packet are in the skb's linear area, but the remaining ~63KB are in the frag_list where skb_copy_bits is needed to read data. Initially, the idea was to add a configurable limit via a new sysctl knob with default 8, in line with knobs from commit 47d3d7ac656a ("ipv6: Implement limits on Hop-by-Hop and Destination options"), but two reasons eventually argued against it: - It adds to UAPI that needs to be maintained forever, and upcoming work is restricting extension header ordering anyway, leaving little reason for another sysctl knob - exthdrs_core.c is always built-in even when CONFIG_IPV6=n, where struct net has no .ipv6 member, so the read site would need an ifdef'd fallback to a constant anyway Therefore, just use a constant (IP6_MAX_EXT_HDRS_CNT). All four extension header walking functions are now bound by this limit. Note that the check in ip6_protocol_deliver_rcu() happens right before the goto resubmit, such that we don't have to have a test for ipv6_ext_hdr() in the fast-path. There's an ongoing IETF draft-iurman-6man-eh-occurrences to enforce IPv6 extension headers ordering and occurrence. The latter also discusses security implications. As per RFC8200 section 4.1, the occurrence rules for extension headers provide a practical upper bound which is 8. In order to be conservative, let's define IP6_MAX_EXT_HDRS_CNT as 12 to leave enough room for quirky setups. In the unlikely event that this is still not enough, then we might need to reconsider a sysctl. Signed-off-by: Daniel Borkmann Reviewed-by: Ido Schimmel Reviewed-by: Eric Dumazet Reviewed-by: Justin Iurman Link: https://patch.msgid.link/20260429154648.809751-1-daniel@iogearbox.net Signed-off-by: Jakub Kicinski

bpf: remove ipv6_bpf_stub completely and use direct function calls

2026-03-29T18:21:24+00:00

As IPv6 is built-in only, the ipv6_bpf_stub can be removed completely. Convert all ipv6_bpf_stub usage to direct function calls instead. The fallback functions introduced previously will prevent linkage errors when CONFIG_IPV6 is disabled. Signed-off-by: Fernando Fernandez Mancera Tested-by: Ricardo B. Marlière Acked-by: Daniel Borkmann Reviewed-by: Martin KaFai Lau Link: https://patch.msgid.link/20260325120928.15848-10-fmancera@suse.de Signed-off-by: Jakub Kicinski

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: Retire UDP-Lite.

2026-03-14T01:57:44+00:00

As announced in commit be28c14ac8bb ("udplite: Print deprecation notice."), it's time to deprecate UDP-Lite. As a first step, let's drop support for IPv6 UDP-Lite sockets. We will remove the remaining dead code gradually. Along with the removal of udplite.c, most of the functions exposed via udp_impl.h are made static. The prototypes of udpv6_sendmsg() and udpv6_recvmsg() are moved to udp.h, but only udpv6_recvmsg() has INDIRECT_CALLABLE_DECLARE() because udpv6_sendmsg() is exported for rxrpc since commit ed472b0c8783 ("rxrpc: Call udp_sendmsg() directly"). Also, udpv6_recvmsg() needs INDIRECT_CALLABLE_SCOPE for CONFIG_MITIGATION_RETPOLINE=n. Note that udplite.h is included temporarily for udplite_csum(). Signed-off-by: Kuniyuki Iwashima Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260311052020.1213705-3-kuniyu@google.com Signed-off-by: Jakub Kicinski

net: remove addr_len argument of recvmsg() handlers

2026-03-03T02:17:17+00:00

Use msg->msg_namelen as a place holder instead of a temporary variable, notably in inet[6]_recvmsg(). This removes stack canaries and allows tail-calls. $ scripts/bloat-o-meter -t vmlinux.old vmlinux add/remove: 0/0 grow/shrink: 2/19 up/down: 26/-532 (-506) Function old new delta rawv6_recvmsg 744 767 +23 vsock_dgram_recvmsg 55 58 +3 vsock_connectible_recvmsg 50 47 -3 unix_stream_recvmsg 161 158 -3 unix_seqpacket_recvmsg 62 59 -3 unix_dgram_recvmsg 42 39 -3 tcp_recvmsg 546 543 -3 mptcp_recvmsg 1568 1565 -3 ping_recvmsg 806 800 -6 tcp_bpf_recvmsg_parser 983 974 -9 ip_recv_error 588 576 -12 ipv6_recv_rxpmtu 442 428 -14 udp_recvmsg 1243 1224 -19 ipv6_recv_error 1046 1024 -22 udpv6_recvmsg 1487 1461 -26 raw_recvmsg 465 437 -28 udp_bpf_recvmsg 1027 984 -43 sock_common_recvmsg 103 27 -76 inet_recvmsg 257 175 -82 inet6_recvmsg 257 175 -82 tcp_bpf_recvmsg 663 568 -95 Total: Before=25143834, After=25143328, chg -0.00% Signed-off-by: Eric Dumazet Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260227151120.1346573-1-edumazet@google.com Signed-off-by: Jakub Kicinski

ipv6: fix a race in ip6_sock_set_v6only()

2026-02-18T00:45:29+00:00

It is unlikely that this function will be ever called with isk->inet_num being not zero. Perform the check on isk->inet_num inside the locked section for complete safety. Fixes: 9b115749acb24 ("ipv6: add ip6_sock_set_v6only") Signed-off-by: Eric Dumazet Reviewed-by: Simon Horman Reviewed-by: Fernando Fernandez Mancera Link: https://patch.msgid.link/20260216102202.3343588-1-edumazet@google.com Signed-off-by: Jakub Kicinski

net/ipv6: Remove HBH helpers

2026-02-07T04:50:13+00:00

Now that the HBH jumbo helpers are not used by any driver or GSO, remove them altogether. Signed-off-by: Alice Mikityanska Acked-by: Paolo Abeni Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260205133925.526371-13-alice.kernel@fastmail.im Signed-off-by: Jakub Kicinski

net/ipv6: Introduce payload_len helpers

2026-02-07T04:50:03+00:00

The next commits will transition away from using the hop-by-hop extension header to encode packet length for BIG TCP. Add wrappers around ip6->payload_len that return the actual value if it's non-zero, and calculate it from skb->len if payload_len is set to zero (and a symmetrical setter). The new helpers are used wherever the surrounding code supports the hop-by-hop jumbo header for BIG TCP IPv6, or the corresponding IPv4 code uses skb_ip_totlen (e.g., in include/net/netfilter/nf_tables_ipv6.h). No behavioral change in this commit. Signed-off-by: Alice Mikityanska Acked-by: Paolo Abeni Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260205133925.526371-2-alice.kernel@fastmail.im Signed-off-by: Jakub Kicinski

ipv6: colocate inet6_cork in inet_cork_full

2026-02-03T01:49:30+00:00

All inet6_cork users also use one inet_cork_full. Reduce number of parameters and increase data locality. This saves ~275 bytes of code on x86_64. Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20260130210303.3888261-9-edumazet@google.com Signed-off-by: Jakub Kicinski