linux-stable.git/include/net/ip.h, branch v7.2.3 Linux kernel stable tree net: advertise TCP MSS from the configured MTU, not the learned PMTU 2026-09-02T12:33:19+00:00 Jiayuan Chen jiayuan.chen@linux.dev 2026-08-15T07:03:36+00:00 713ed6ce111e8f5162454bae12df4e7b27d35708 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 <jiayuan.chen@linux.dev> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260815070413.294559-1-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
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 <jiayuan.chen@linux.dev>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260815070413.294559-1-jiayuan.chen@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
net: remove EXPORT_IPV6_MOD() and EXPORT_IPV6_MOD_GPL() macros 2026-03-29T18:21:22+00:00 Fernando Fernandez Mancera fmancera@suse.de 2026-03-25T12:08:43+00:00 0557a34487b10f3e600a3a20b98ea164f36a3ad2 As IPv6 is built-in only, the macro is always evaluating to an empty one. Remove it completely from the code. Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de> Link: https://patch.msgid.link/20260325120928.15848-3-fmancera@suse.de Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
As IPv6 is built-in only, the macro is always evaluating to an empty
one. Remove it completely from the code.

Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Link: https://patch.msgid.link/20260325120928.15848-3-fmancera@suse.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2026-03-05T20:11:05+00:00 Jakub Kicinski kuba@kernel.org 2026-02-26T18:20:47+00:00 0b1324cdd8de9f54f9daf689a4ae59783c333510 Cross-merge networking fixes after downstream PR (net-7.0-rc3). No conflicts. Adjacent changes: net/netfilter/nft_set_rbtree.c fb7fb4016300 ("netfilter: nf_tables: clone set on flush only") 3aea466a4399 ("netfilter: nft_set_rbtree: don't disable bh when acquiring tree lock") Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
Cross-merge networking fixes after downstream PR (net-7.0-rc3).

No conflicts.

Adjacent changes:

net/netfilter/nft_set_rbtree.c
  fb7fb4016300 ("netfilter: nf_tables: clone set on flush only")
  3aea466a4399 ("netfilter: nft_set_rbtree: don't disable bh when acquiring tree lock")

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
net: remove addr_len argument of recvmsg() handlers 2026-03-03T02:17:17+00:00 Eric Dumazet edumazet@google.com 2026-02-27T15:11:20+00:00 8341c989ac77d712c7d6e2bce29e8a4bcb2eeae4 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 <edumazet@google.com> Reviewed-by: Willem de Bruijn <willemb@google.com> Link: https://patch.msgid.link/20260227151120.1346573-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
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 <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260227151120.1346573-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
inet: annotate data-races around isk->inet_num 2026-02-28T01:16:59+00:00 Eric Dumazet edumazet@google.com 2026-02-25T20:35:45+00:00 29252397bcc1e0a1f85e5c3bee59c325f5c26341 UDP/TCP lookups are using RCU, thus isk->inet_num accesses should use READ_ONCE() and WRITE_ONCE() where needed. Fixes: 3ab5aee7fe84 ("net: Convert TCP & DCCP hash tables to use RCU / hlist_nulls") Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com> Link: https://patch.msgid.link/20260225203545.1512417-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
UDP/TCP lookups are using RCU, thus isk->inet_num accesses
should use READ_ONCE() and WRITE_ONCE() where needed.

Fixes: 3ab5aee7fe84 ("net: Convert TCP & DCCP hash tables to use RCU / hlist_nulls")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260225203545.1512417-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
net: Convert proto callbacks from sockaddr to sockaddr_unsized 2025-11-05T03:10:33+00:00 Kees Cook kees@kernel.org 2025-11-04T00:26:13+00:00 449f68f8fffa2c41fc265730bd05a3c4947916c1 Convert struct proto pre_connect(), connect(), bind(), and bind_add() callback function prototypes from struct sockaddr to struct sockaddr_unsized. This does not change per-implementation use of sockaddr for passing around an arbitrarily sized sockaddr struct. Those will be addressed in future patches. Additionally removes the no longer referenced struct sockaddr from include/net/inet_common.h. No binary changes expected. Signed-off-by: Kees Cook <kees@kernel.org> Link: https://patch.msgid.link/20251104002617.2752303-5-kees@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
Convert struct proto pre_connect(), connect(), bind(), and bind_add()
callback function prototypes from struct sockaddr to struct sockaddr_unsized.
This does not change per-implementation use of sockaddr for passing around
an arbitrarily sized sockaddr struct. Those will be addressed in future
patches.

Additionally removes the no longer referenced struct sockaddr from
include/net/inet_common.h.

No binary changes expected.

Signed-off-by: Kees Cook <kees@kernel.org>
Link: https://patch.msgid.link/20251104002617.2752303-5-kees@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
net: snmp: remove SNMP_MIB_SENTINEL 2025-09-09T01:06:21+00:00 Eric Dumazet edumazet@google.com 2025-09-05T16:58:13+00:00 20d3d26815441d03a9a15114729faaa54957baba No more user of SNMP_MIB_SENTINEL, we can remove it. Also remove snmp_get_cpu_field[64]_batch() helpers. Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Sabrina Dubroca <sd@queasysnail.net> Link: https://patch.msgid.link/20250905165813.1470708-10-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
No more user of SNMP_MIB_SENTINEL, we can remove it.

Also remove snmp_get_cpu_field[64]_batch() helpers.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20250905165813.1470708-10-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
ipv6: snmp: do not use SNMP_MIB_SENTINEL anymore 2025-09-09T01:06:20+00:00 Eric Dumazet edumazet@google.com 2025-09-05T16:58:06+00:00 ceac1fb2290d230eb83aff3761058c559440de13 Use ARRAY_SIZE(), so that we know the limit at compile time. Following patch needs this preliminary change. Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Sabrina Dubroca <sd@queasysnail.net> Link: https://patch.msgid.link/20250905165813.1470708-3-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
Use ARRAY_SIZE(), so that we know the limit at compile time.

Following patch needs this preliminary change.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20250905165813.1470708-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
net: use dst_dev_rcu() in sk_setup_caps() 2025-08-30T02:36:32+00:00 Eric Dumazet edumazet@google.com 2025-08-28T19:58:20+00:00 99a2ace61b211b0be861b07fbaa062fca4b58879 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 <edumazet@google.com> Reviewed-by: David Ahern <dsahern@kernel.org> Link: https://patch.msgid.link/20250828195823.3958522-6-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
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 <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250828195823.3958522-6-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
ipv4: adopt dst_dev, skb_dst_dev and skb_dst_dev_net[_rcu] 2025-07-02T21:32:30+00:00 Eric Dumazet edumazet@google.com 2025-06-30T12:19:31+00:00 a74fc62eec155ca5a6da8ff3856f3dc87fe24558 Use the new helpers as a first step to deal with potential dst->dev races. Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com> Link: https://patch.msgid.link/20250630121934.3399505-8-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
Use the new helpers as a first step to deal with
potential dst->dev races.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250630121934.3399505-8-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>