[PATCH net-next v5.0 09/19] net: psp: update the TCP MSS to reflect PSP packet overhead
From: Daniel Zahka <daniel.zahka@gmail.com>
Date: 2025-07-23 20:35:30
Subsystem:
networking [general], networking [ipv4/ipv6], networking [tcp], psp security protocol, the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Neal Cardwell, Daniel Zahka, Willem de Bruijn, Linus Torvalds
From: Jakub Kicinski <kuba@kernel.org>
PSP eats 32B of header space. Adjust MSS appropriately.
We can either modify tcp_mtu_to_mss() / tcp_mss_to_mtu()
or reuse icsk_ext_hdr_len. The former option is more TCP
specific and has runtime overhead. The latter is a bit
of a hack as PSP is not an ext_hdr. If one squints hard
enough, UDP encap is just a more practical version of
IPv6 exthdr, so go with the latter. Happy to change.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
---
Notes:
v1:
- https://lore.kernel.org/netdev/20240510030435.120935-8-kuba@kernel.org/ (local)
include/net/psp/functions.h | 12 ++++++++++++
include/net/psp/types.h | 3 +++
net/ipv4/tcp_ipv4.c | 4 ++--
net/ipv6/ipv6_sockglue.c | 6 +++++-
net/ipv6/tcp_ipv6.c | 6 +++---
net/psp/psp_sock.c | 5 +++++
6 files changed, 30 insertions(+), 6 deletions(-)
diff --git a/include/net/psp/functions.h b/include/net/psp/functions.h
index bf703dcf353f..17642c944620 100644
--- a/include/net/psp/functions.h
+++ b/include/net/psp/functions.h@@ -139,6 +139,13 @@ static inline struct psp_assoc *psp_skb_get_assoc_rcu(struct sk_buff *skb) return psp_sk_get_assoc_rcu(skb->sk); } + +static inline unsigned int psp_sk_overhead(const struct sock *sk) +{ + bool has_psp = rcu_access_pointer(sk->psp_assoc); + + return has_psp ? PSP_HDR_SIZE + PSP_TRL_SIZE : 0; +} #else static inline void psp_sk_assoc_free(struct sock *sk) { } static inline void
@@ -178,6 +185,11 @@ static inline struct psp_assoc *psp_skb_get_assoc_rcu(struct sk_buff *skb) { return NULL; } + +static inline unsigned int psp_sk_overhead(const struct sock *sk) +{ + return 0; +} #endif static inline unsigned long
diff --git a/include/net/psp/types.h b/include/net/psp/types.h
index b0e32e7165a3..f93ad0e6c04f 100644
--- a/include/net/psp/types.h
+++ b/include/net/psp/types.h@@ -93,6 +93,9 @@ struct psp_dev_caps { #define PSP_MAX_KEY 32 +#define PSP_HDR_SIZE 16 /* We don't support optional fields, yet */ +#define PSP_TRL_SIZE 16 /* AES-GCM/GMAC trailer size */ + struct psp_skb_ext { __be32 spi; u16 dev_id;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 35e2a1ce87b8..3c3e8760f89b 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c@@ -293,9 +293,9 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len) inet->inet_dport = usin->sin_port; sk_daddr_set(sk, daddr); - inet_csk(sk)->icsk_ext_hdr_len = 0; + inet_csk(sk)->icsk_ext_hdr_len = psp_sk_overhead(sk); if (inet_opt) - inet_csk(sk)->icsk_ext_hdr_len = inet_opt->opt.optlen; + inet_csk(sk)->icsk_ext_hdr_len += inet_opt->opt.optlen; tp->rx_opt.mss_clamp = TCP_MSS_DEFAULT;
diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index e66ec623972e..a61e742794f9 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c@@ -49,6 +49,7 @@ #include <net/xfrm.h> #include <net/compat.h> #include <net/seg6.h> +#include <net/psp.h> #include <linux/uaccess.h>
@@ -107,7 +108,10 @@ struct ipv6_txoptions *ipv6_update_options(struct sock *sk, !((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE)) && inet_sk(sk)->inet_daddr != LOOPBACK4_IPV6) { struct inet_connection_sock *icsk = inet_csk(sk); - icsk->icsk_ext_hdr_len = opt->opt_flen + opt->opt_nflen; + + icsk->icsk_ext_hdr_len = + psp_sk_overhead(sk) + + opt->opt_flen + opt->opt_nflen; icsk->icsk_sync_mss(sk, icsk->icsk_pmtu_cookie); } }
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 6a89edda31c7..adf83ec25b66 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c@@ -302,10 +302,10 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr, sk->sk_gso_type = SKB_GSO_TCPV6; ip6_dst_store(sk, dst, NULL, NULL); - icsk->icsk_ext_hdr_len = 0; + icsk->icsk_ext_hdr_len = psp_sk_overhead(sk); if (opt) - icsk->icsk_ext_hdr_len = opt->opt_flen + - opt->opt_nflen; + icsk->icsk_ext_hdr_len += opt->opt_flen + + opt->opt_nflen; tp->rx_opt.mss_clamp = IPV6_MIN_MTU - sizeof(struct tcphdr) - sizeof(struct ipv6hdr);
diff --git a/net/psp/psp_sock.c b/net/psp/psp_sock.c
index 757fc9698f3d..7aee69ed10cd 100644
--- a/net/psp/psp_sock.c
+++ b/net/psp/psp_sock.c@@ -180,6 +180,7 @@ int psp_sock_assoc_set_tx(struct sock *sk, struct psp_dev *psd, u32 version, struct psp_key_parsed *key, struct netlink_ext_ack *extack) { + struct inet_connection_sock *icsk; struct psp_assoc *pas, *dummy; int err;
@@ -231,6 +232,10 @@ int psp_sock_assoc_set_tx(struct sock *sk, struct psp_dev *psd, tcp_write_collapse_fence(sk); pas->upgrade_seq = tcp_sk(sk)->rcv_nxt; + icsk = inet_csk(sk); + icsk->icsk_ext_hdr_len += psp_sk_overhead(sk); + icsk->icsk_sync_mss(sk, icsk->icsk_pmtu_cookie); + exit_free_dummy: kfree(dummy); exit_unlock:
--
2.47.1