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net: psp: update the TCP MSS to reflect PSP packet overhead

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PSP eats 40B 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.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250917000954.859376-10-daniel.zahka@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Jakub Kicinski
2025-09-16 17:09:36 -07:00
committed by Paolo Abeni
parent 6b46ca260e
commit e97269257f
6 changed files with 32 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
include/net/psp/functions.h
View File

@@ -5,6 +5,7 @@
#include <linux/skbuff.h>
#include <linux/rcupdate.h>
#include <linux/udp.h>
#include <net/sock.h>
#include <net/tcp.h>
#include <net/psp/types.h>
@@ -143,6 +144,14 @@ 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)
{
int psp_encap = sizeof(struct udphdr) + PSP_HDR_SIZE + PSP_TRL_SIZE;
bool has_psp = rcu_access_pointer(sk->psp_assoc);
return has_psp ? psp_encap : 0;
}
#else
static inline void psp_sk_assoc_free(struct sock *sk) { }
static inline void
@@ -182,6 +191,11 @@ 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

3
include/net/psp/types.h
View File

@@ -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;

4
net/ipv4/tcp_ipv4.c
View File

@@ -294,9 +294,9 @@ 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;

6
net/ipv6/ipv6_sockglue.c
View File

@@ -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);
}
}

6
net/ipv6/tcp_ipv6.c
View File

@@ -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);

5
net/psp/psp_sock.c
View File

@@ -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;
@@ -236,6 +237,10 @@ 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: