FAILED: patch "[PATCH] tcp: clamp route advmss to TCP_MIN_MSS" failed to apply to 6.6-stable tree

FAILED: patch "[PATCH] tcp: clamp route advmss to TCP_MIN_MSS" failed to apply to 6.6-stable tree

[gregkh]

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026083105-buddhist-verdict-4f97@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1 Mon Sep 17 00:00:00 2001
From: Yong Wang <edragain@163.com>
Date: Wed, 19 Aug 2026 23:22:04 +0800
Subject: [PATCH] tcp: clamp route advmss to TCP_MIN_MSS

tcp_select_initial_window() assumes that callers never pass an MSS
smaller than 1, but route-derived advmss values can violate that
assumption.

A too-small explicit RTAX_ADVMSS is one way to get there, but it is not
the only one. The same divide-by-zero can also be reached through the
"default advmss" path when RTAX_ADVMSS is left at 0 and the effective
advmss is later driven down by route MTU and min_adv_mss.

Introduce a tcp_dst_advmss() helper that clamps route advmss to
TCP_MIN_MSS before TCP consumes it, and use it in the TCP paths that
derive advmss from dst metrics. This keeps the effective MSS from
dropping to zero before tcp_select_initial_window() rounds the receive
window.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Yong Wang <edragain@163.com>
Signed-off-by: Ren Wei <weir@nebusec.ai>
Link: https://patch.msgid.link/251eaf8277fa7c66364c9815c5da01662d269181.1787074852.git.edragain@163.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 2c5b889530b5..670c20876f26 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1782,6 +1782,11 @@ static inline int tcp_full_space(const struct sock *sk)
 	return tcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf));
 }
 
+static inline u32 tcp_dst_advmss(const struct dst_entry *dst)
+{
+	return max_t(u32, dst_metric_advmss(dst), TCP_MIN_MSS);
+}
+
 static inline void __tcp_adjust_rcv_ssthresh(struct sock *sk, u32 new_ssthresh)
 {
 	int unused_mem = sk_unused_reserved_mem(sk);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 190c7af4cf92..9f053eb8b46e 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1736,7 +1736,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
 	tcp_ca_openreq_child(newsk, dst);
 
 	tcp_sync_mss(newsk, dst4_mtu(dst));
-	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst));
+	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), tcp_dst_advmss(dst));
 
 	tcp_initialize_rcv_mss(newsk);
 
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 12254e6eb2f3..f3fa0b18eda0 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -440,7 +440,7 @@ void tcp_openreq_init_rwin(struct request_sock *req,
 	u32 rcv_wnd;
 	int mss;
 
-	mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
+	mss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
 	window_clamp = READ_ONCE(tp->window_clamp);
 	/* Set this up on the first call only */
 	req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index fcaa04e65189..f2709d585edb 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -143,7 +143,7 @@ static __u16 tcp_advertise_mss(struct sock *sk)
 	int mss = tp->advmss;
 
 	if (dst) {
-		unsigned int metric = dst_metric_advmss(dst);
+		unsigned int metric = tcp_dst_advmss(dst);
 
 		if (metric < mss) {
 			mss = metric;
@@ -3972,7 +3972,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 	}
 	skb_dst_set(skb, dst);
 
-	mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
+	mss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
 
 	memset(&opts, 0, sizeof(opts));
 	now = tcp_clock_ns();
@@ -4128,7 +4128,7 @@ static void tcp_connect_init(struct sock *sk)
 
 	if (!tp->window_clamp)
 		WRITE_ONCE(tp->window_clamp, dst_metric(dst, RTAX_WINDOW));
-	tp->advmss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
+	tp->advmss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
 
 	tcp_initialize_rcv_mss(sk);
 
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 9e9155b1b3aa..df9c29eb5c1f 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1487,7 +1487,7 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
 	tcp_ca_openreq_child(newsk, dst);
 
 	tcp_sync_mss(newsk, dst6_mtu(dst));
-	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst));
+	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), tcp_dst_advmss(dst));
 
 	tcp_initialize_rcv_mss(newsk);
 

[PATCH 6.6.y 1/5] ipv6: pass proto by value to ipv6_push_nfrag_opts() and ipv6_push_frag_opts()

[Sasha Levin]

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 1bc46dd209667346c5aa56c351995e7c260696d0 ]

With CONFIG_STACKPROTECTOR_STRONG=y, it is better to avoid passing
a pointer to an automatic variable.

Change these exported functions to return 'u8 proto'
instead of void.

- ipv6_push_nfrag_opts()
- ipv6_push_frag_opts()

For instance, replace
	ipv6_push_frag_opts(skb, opt, &proto);
with:
	proto = ipv6_push_frag_opts(skb, opt, proto);

Note that even after this change, ip6_xmit() has to use a stack canary
because of @first_hop variable.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260130210303.3888261-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 870a9e42ecc6 ("tcp: clamp route advmss to TCP_MIN_MSS")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/net/ipv6.h    | 10 ++++----
 net/ipv6/exthdrs.c    | 55 +++++++++++++++++++++++--------------------
 net/ipv6/ip6_output.c | 19 ++++++++-------
 net/ipv6/ip6_tunnel.c |  2 +-
 4 files changed, 46 insertions(+), 40 deletions(-)

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 3645776d71c9c..7f7796ab320a6 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -1154,11 +1154,11 @@ int ip6_local_out(struct net *net, struct sock *sk, struct sk_buff *skb);
  *	Extension header (options) processing
  */
 
-void ipv6_push_nfrag_opts(struct sk_buff *skb, struct ipv6_txoptions *opt,
-			  u8 *proto, struct in6_addr **daddr_p,
-			  struct in6_addr *saddr);
-void ipv6_push_frag_opts(struct sk_buff *skb, struct ipv6_txoptions *opt,
-			 u8 *proto);
+u8 ipv6_push_nfrag_opts(struct sk_buff *skb, struct ipv6_txoptions *opt,
+			u8 proto, struct in6_addr **daddr_p,
+			struct in6_addr *saddr);
+u8 ipv6_push_frag_opts(struct sk_buff *skb, struct ipv6_txoptions *opt,
+		       u8 proto);
 
 int ipv6_skip_exthdr(const struct sk_buff *, int start, u8 *nexthdrp,
 		     __be16 *frag_offp);
diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index e024d8da431c4..9641c37cfd177 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -1107,9 +1107,9 @@ int ipv6_parse_hopopts(struct sk_buff *skb)
  *	for headers.
  */
 
-static void ipv6_push_rthdr0(struct sk_buff *skb, u8 *proto,
-			     struct ipv6_rt_hdr *opt,
-			     struct in6_addr **addr_p, struct in6_addr *saddr)
+static u8 ipv6_push_rthdr0(struct sk_buff *skb, u8 proto,
+			   struct ipv6_rt_hdr *opt,
+			   struct in6_addr **addr_p, struct in6_addr *saddr)
 {
 	struct rt0_hdr *phdr, *ihdr;
 	int hops;
@@ -1128,13 +1128,13 @@ static void ipv6_push_rthdr0(struct sk_buff *skb, u8 *proto,
 	phdr->addr[hops - 1] = **addr_p;
 	*addr_p = ihdr->addr;
 
-	phdr->rt_hdr.nexthdr = *proto;
-	*proto = NEXTHDR_ROUTING;
+	phdr->rt_hdr.nexthdr = proto;
+	return NEXTHDR_ROUTING;
 }
 
-static void ipv6_push_rthdr4(struct sk_buff *skb, u8 *proto,
-			     struct ipv6_rt_hdr *opt,
-			     struct in6_addr **addr_p, struct in6_addr *saddr)
+static u8 ipv6_push_rthdr4(struct sk_buff *skb, u8 proto,
+			   struct ipv6_rt_hdr *opt,
+			   struct in6_addr **addr_p, struct in6_addr *saddr)
 {
 	struct ipv6_sr_hdr *sr_phdr, *sr_ihdr;
 	int plen, hops;
@@ -1177,58 +1177,61 @@ static void ipv6_push_rthdr4(struct sk_buff *skb, u8 *proto,
 	}
 #endif
 
-	sr_phdr->nexthdr = *proto;
-	*proto = NEXTHDR_ROUTING;
+	sr_phdr->nexthdr = proto;
+	return NEXTHDR_ROUTING;
 }
 
-static void ipv6_push_rthdr(struct sk_buff *skb, u8 *proto,
-			    struct ipv6_rt_hdr *opt,
-			    struct in6_addr **addr_p, struct in6_addr *saddr)
+static u8 ipv6_push_rthdr(struct sk_buff *skb, u8 proto,
+			  struct ipv6_rt_hdr *opt,
+			  struct in6_addr **addr_p, struct in6_addr *saddr)
 {
 	switch (opt->type) {
 	case IPV6_SRCRT_TYPE_0:
 	case IPV6_SRCRT_STRICT:
 	case IPV6_SRCRT_TYPE_2:
-		ipv6_push_rthdr0(skb, proto, opt, addr_p, saddr);
+		proto = ipv6_push_rthdr0(skb, proto, opt, addr_p, saddr);
 		break;
 	case IPV6_SRCRT_TYPE_4:
-		ipv6_push_rthdr4(skb, proto, opt, addr_p, saddr);
+		proto = ipv6_push_rthdr4(skb, proto, opt, addr_p, saddr);
 		break;
 	default:
 		break;
 	}
+	return proto;
 }
 
-static void ipv6_push_exthdr(struct sk_buff *skb, u8 *proto, u8 type, struct ipv6_opt_hdr *opt)
+static u8 ipv6_push_exthdr(struct sk_buff *skb, u8 proto, u8 type, struct ipv6_opt_hdr *opt)
 {
 	struct ipv6_opt_hdr *h = skb_push(skb, ipv6_optlen(opt));
 
 	memcpy(h, opt, ipv6_optlen(opt));
-	h->nexthdr = *proto;
-	*proto = type;
+	h->nexthdr = proto;
+	return type;
 }
 
-void ipv6_push_nfrag_opts(struct sk_buff *skb, struct ipv6_txoptions *opt,
-			  u8 *proto,
-			  struct in6_addr **daddr, struct in6_addr *saddr)
+u8 ipv6_push_nfrag_opts(struct sk_buff *skb, struct ipv6_txoptions *opt,
+			u8 proto,
+			struct in6_addr **daddr, struct in6_addr *saddr)
 {
 	if (opt->srcrt) {
-		ipv6_push_rthdr(skb, proto, opt->srcrt, daddr, saddr);
+		proto = ipv6_push_rthdr(skb, proto, opt->srcrt, daddr, saddr);
 		/*
 		 * IPV6_RTHDRDSTOPTS is ignored
 		 * unless IPV6_RTHDR is set (RFC3542).
 		 */
 		if (opt->dst0opt)
-			ipv6_push_exthdr(skb, proto, NEXTHDR_DEST, opt->dst0opt);
+			proto = ipv6_push_exthdr(skb, proto, NEXTHDR_DEST, opt->dst0opt);
 	}
 	if (opt->hopopt)
-		ipv6_push_exthdr(skb, proto, NEXTHDR_HOP, opt->hopopt);
+		proto = ipv6_push_exthdr(skb, proto, NEXTHDR_HOP, opt->hopopt);
+	return proto;
 }
 
-void ipv6_push_frag_opts(struct sk_buff *skb, struct ipv6_txoptions *opt, u8 *proto)
+u8 ipv6_push_frag_opts(struct sk_buff *skb, struct ipv6_txoptions *opt, u8 proto)
 {
 	if (opt->dst1opt)
-		ipv6_push_exthdr(skb, proto, NEXTHDR_DEST, opt->dst1opt);
+		proto = ipv6_push_exthdr(skb, proto, NEXTHDR_DEST, opt->dst1opt);
+	return proto;
 }
 EXPORT_SYMBOL(ipv6_push_frag_opts);
 
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 2d18b2dcbafb1..b065fc70037c4 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -299,11 +299,12 @@ int ip6_xmit(const struct sock *sk, struct sk_buff *skb, struct flowi6 *fl6,
 		seg_len += opt->opt_nflen + opt->opt_flen;
 
 		if (opt->opt_flen)
-			ipv6_push_frag_opts(skb, opt, &proto);
+			proto = ipv6_push_frag_opts(skb, opt, proto);
 
 		if (opt->opt_nflen)
-			ipv6_push_nfrag_opts(skb, opt, &proto, &first_hop,
-					     &fl6->saddr);
+			proto = ipv6_push_nfrag_opts(skb, opt, proto,
+						     &first_hop,
+						     &fl6->saddr);
 	}
 
 	if (unlikely(seg_len > IPV6_MAXPLEN)) {
@@ -1930,11 +1931,13 @@ struct sk_buff *__ip6_make_skb(struct sock *sk,
 	__skb_pull(skb, skb_network_header_len(skb));
 
 	final_dst = &fl6->daddr;
-	if (opt && opt->opt_flen)
-		ipv6_push_frag_opts(skb, opt, &proto);
-	if (opt && opt->opt_nflen)
-		ipv6_push_nfrag_opts(skb, opt, &proto, &final_dst, &fl6->saddr);
-
+	if (opt) {
+		if (opt->opt_flen)
+			proto = ipv6_push_frag_opts(skb, opt, proto);
+		if (opt->opt_nflen)
+			proto = ipv6_push_nfrag_opts(skb, opt, proto,
+						     &final_dst, &fl6->saddr);
+	}
 	skb_push(skb, sizeof(struct ipv6hdr));
 	skb_reset_network_header(skb);
 	hdr = ipv6_hdr(skb);
diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index dfabd9969b3f3..9d4614622ea6a 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1271,7 +1271,7 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev, __u8 dsfield,
 
 	if (encap_limit >= 0) {
 		init_tel_txopt(&opt, encap_limit);
-		ipv6_push_frag_opts(skb, &opt.ops, &proto);
+		proto = ipv6_push_frag_opts(skb, &opt.ops, proto);
 	}
 
 	skb_push(skb, sizeof(struct ipv6hdr));
-- 
2.53.0

[PATCH 6.6.y 2/5] inet: add dst4_mtu() and dst6_mtu() helpers

[Sasha Levin]

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 8776c4ef3ab22b95f55713f00a7a576e6402507d ]

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 <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260130210303.3888261-6-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 870a9e42ecc6 ("tcp: clamp route advmss to TCP_MIN_MSS")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/net/dst.h       | 6 ++++++
 include/net/ip6_route.h | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/include/net/dst.h b/include/net/dst.h
index 55d1be268d243..e1c4a806597da 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -216,6 +216,12 @@ static inline u32 dst_mtu(const struct dst_entry *dst)
 	return INDIRECT_CALL_INET(dst->ops->mtu, ip6_mtu, ipv4_mtu, dst);
 }
 
+/* Variant of dst_mtu() for IPv4 users. */
+static inline u32 dst4_mtu(const struct dst_entry *dst)
+{
+	return INDIRECT_CALL_1(dst->ops->mtu, ipv4_mtu, dst);
+}
+
 /* RTT metrics are stored in milliseconds for user ABI, but used as jiffies */
 static inline unsigned long dst_metric_rtt(const struct dst_entry *dst, int metric)
 {
diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 392232fcd703c..55c9ccfa0bcb8 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -266,6 +266,12 @@ static inline bool ipv6_anycast_destination(const struct dst_entry *dst,
 int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 		 int (*output)(struct net *, struct sock *, struct sk_buff *));
 
+/* Variant of dst_mtu() for IPv6 users */
+static inline u32 dst6_mtu(const struct dst_entry *dst)
+{
+	return INDIRECT_CALL_1(dst->ops->mtu, ip6_mtu, dst);
+}
+
 static inline unsigned int ip6_skb_dst_mtu(const struct sk_buff *skb)
 {
 	const struct ipv6_pinfo *np = skb->sk && !dev_recursion_level() ?
-- 
2.53.0

[PATCH 6.6.y 3/5] ipv6: use dst6_mtu() instead of dst_mtu()

[Sasha Levin]

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit b40f0130a23b6bab8b359e158a40af81f11f14be ]

When we expect an IPv6 dst, use dst6_mtu() instead of dst_mtu()
to save some code space.

Due to current dst6_mtu() implementation, only convert
users in IPv6 stack.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260130210303.3888261-7-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 870a9e42ecc6 ("tcp: clamp route advmss to TCP_MIN_MSS")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv6/ip6_gre.c       |  3 ++-
 net/ipv6/ip6_output.c    |  6 +++---
 net/ipv6/ip6_tunnel.c    |  4 ++--
 net/ipv6/ipv6_sockglue.c |  4 ++--
 net/ipv6/route.c         | 10 ++++++----
 net/ipv6/tcp_ipv6.c      |  9 +++++----
 6 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 74442c9fb4abc..3e635cc6d0646 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -1071,9 +1071,10 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb,
 	gre_build_header(skb, 8, TUNNEL_SEQ, proto, 0, htonl(atomic_fetch_inc(&t->o_seqno)));
 
 	/* TooBig packet may have updated dst->dev's mtu */
-	if (!t->parms.collect_md && dst && dst_mtu(dst) > dst->dev->mtu)
+	if (!t->parms.collect_md && dst && dst6_mtu(dst) > dst->dev->mtu)
 		dst->ops->update_pmtu(dst, NULL, skb, dst->dev->mtu, false);
 
+
 	err = ip6_tnl_xmit(skb, dev, dsfield, &fl6, encap_limit, &mtu,
 			   NEXTHDR_GRE);
 	if (err != 0) {
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index b065fc70037c4..856b1ab2d629f 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -347,7 +347,7 @@ int ip6_xmit(const struct sock *sk, struct sk_buff *skb, struct flowi6 *fl6,
 	skb->priority = priority;
 	skb->mark = mark;
 
-	mtu = dst_mtu(dst);
+	mtu = dst6_mtu(dst);
 	if ((skb->len <= mtu) || skb->ignore_df || skb_is_gso(skb)) {
 		IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTREQUESTS);
 
@@ -1396,10 +1396,10 @@ static int ip6_setup_cork(struct sock *sk, struct inet_cork_full *cork,
 	v6_cork->tclass = ipc6->tclass;
 	if (rt->dst.flags & DST_XFRM_TUNNEL)
 		mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
-		      READ_ONCE(rt->dst.dev->mtu) : dst_mtu(&rt->dst);
+		      READ_ONCE(rt->dst.dev->mtu) : dst6_mtu(&rt->dst);
 	else
 		mtu = np->pmtudisc >= IPV6_PMTUDISC_PROBE ?
-			READ_ONCE(rt->dst.dev->mtu) : dst_mtu(xfrm_dst_path(&rt->dst));
+			READ_ONCE(rt->dst.dev->mtu) : dst6_mtu(xfrm_dst_path(&rt->dst));
 	if (np->frag_size < mtu) {
 		if (np->frag_size)
 			mtu = np->frag_size;
diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 9d4614622ea6a..712fa475c9664 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -641,7 +641,7 @@ ip4ip6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 
 	/* change mtu on this route */
 	if (rel_type == ICMP_DEST_UNREACH && rel_code == ICMP_FRAG_NEEDED) {
-		if (rel_info > dst_mtu(skb_dst(skb2)))
+		if (rel_info > dst6_mtu(skb_dst(skb2)))
 			goto out;
 
 		skb_dst_update_pmtu_no_confirm(skb2, rel_info);
@@ -1193,7 +1193,7 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev, __u8 dsfield,
 				     t->parms.name);
 		goto tx_err_dst_release;
 	}
-	mtu = dst_mtu(dst) - eth_hlen - psh_hlen - t->tun_hlen;
+	mtu = dst6_mtu(dst) - eth_hlen - psh_hlen - t->tun_hlen;
 	if (encap_limit >= 0) {
 		max_headroom += 8;
 		mtu -= 8;
diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index f106b19b74dd7..65dcf08686795 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -1216,7 +1216,7 @@ int do_ipv6_getsockopt(struct sock *sk, int level, int optname,
 		rcu_read_lock();
 		dst = __sk_dst_get(sk);
 		if (dst)
-			val = dst_mtu(dst);
+			val = dst6_mtu(dst);
 		rcu_read_unlock();
 		if (!val)
 			return -ENOTCONN;
@@ -1315,7 +1315,7 @@ int do_ipv6_getsockopt(struct sock *sk, int level, int optname,
 		rcu_read_lock();
 		dst = __sk_dst_get(sk);
 		if (dst)
-			mtuinfo.ip6m_mtu = dst_mtu(dst);
+			mtuinfo.ip6m_mtu = dst6_mtu(dst);
 		rcu_read_unlock();
 		if (!mtuinfo.ip6m_mtu)
 			return -ENOTCONN;
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 24d097290dbc0..1367dcbd5c719 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2041,6 +2041,8 @@ static void rt6_update_exception_stamp_rt(struct rt6_info *rt)
 static bool rt6_mtu_change_route_allowed(struct inet6_dev *idev,
 					 struct rt6_info *rt, int mtu)
 {
+	u32 dmtu = dst6_mtu(&rt->dst);
+
 	/* If the new MTU is lower than the route PMTU, this new MTU will be the
 	 * lowest MTU in the path: always allow updating the route PMTU to
 	 * reflect PMTU decreases.
@@ -2051,10 +2053,10 @@ static bool rt6_mtu_change_route_allowed(struct inet6_dev *idev,
 	 * handle this.
 	 */
 
-	if (dst_mtu(&rt->dst) >= mtu)
+	if (dmtu >= mtu)
 		return true;
 
-	if (dst_mtu(&rt->dst) == idev->cnf.mtu6)
+	if (dmtu == idev->cnf.mtu6)
 		return true;
 
 	return false;
@@ -2917,7 +2919,7 @@ static void __ip6_rt_update_pmtu(struct dst_entry *dst, const struct sock *sk,
 
 	if (mtu < IPV6_MIN_MTU)
 		return;
-	if (mtu >= dst_mtu(dst))
+	if (mtu >= dst6_mtu(dst))
 		return;
 
 	if (!rt6_cache_allowed_for_pmtu(rt6)) {
@@ -3235,7 +3237,7 @@ EXPORT_SYMBOL_GPL(ip6_sk_redirect);
 static unsigned int ip6_default_advmss(const struct dst_entry *dst)
 {
 	struct net_device *dev = dst->dev;
-	unsigned int mtu = dst_mtu(dst);
+	unsigned int mtu = dst6_mtu(dst);
 	struct net *net;
 
 	mtu -= sizeof(struct ipv6hdr) + sizeof(struct tcphdr);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 689c0b383ebf9..243d398c35868 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -352,7 +352,7 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 static void tcp_v6_mtu_reduced(struct sock *sk)
 {
 	struct dst_entry *dst;
-	u32 mtu;
+	u32 mtu, dmtu;
 
 	if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
 		return;
@@ -369,8 +369,9 @@ static void tcp_v6_mtu_reduced(struct sock *sk)
 	if (!dst)
 		return;
 
-	if (inet_csk(sk)->icsk_pmtu_cookie > dst_mtu(dst)) {
-		tcp_sync_mss(sk, dst_mtu(dst));
+	dmtu = dst6_mtu(dst);
+	if (inet_csk(sk)->icsk_pmtu_cookie > dmtu) {
+		tcp_sync_mss(sk, dmtu);
 		tcp_simple_retransmit(sk);
 	}
 }
@@ -1339,7 +1340,7 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
 
 	tcp_ca_openreq_child(newsk, dst);
 
-	tcp_sync_mss(newsk, dst_mtu(dst));
+	tcp_sync_mss(newsk, dst6_mtu(dst));
 	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst));
 
 	tcp_initialize_rcv_mss(newsk);
-- 
2.53.0

[PATCH 6.6.y 4/5] ipv4: use dst4_mtu() instead of dst_mtu()

[Sasha Levin]

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit fe8570186f100b6cc499b2f7705946baf1388cde ]

When we expect an IPv4 dst, use dst4_mtu() instead of dst_mtu()
to save some code space.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260130210303.3888261-8-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

[ Resolved conflicts in net/ipv4/ip_output.c and net/ipv4/ipmr.c,
  caused by unrelated local/upstream divergence unrelated to this
  commit's own diff:
   - ip_output.c: upstream's pre-image already has
     'pmtudisc = READ_ONCE(inet->pmtudisc);' hoisted out of the if
     condition in __ip_make_skb() (from a commit not present in this
     tree); kept this tree's un-hoisted 'inet->pmtudisc' form and
     applied only the dst_mtu() -> dst4_mtu() substitution.
   - ipmr.c: this tree already has an extra 'dev = rt->dst.dev;'
     line before the MTU check in ipmr_prepare_xmit() that upstream's
     pre-image doesn't carry; kept that line and applied only the
     dst_mtu() -> dst4_mtu() substitution. ]

Stable-dep-of: 870a9e42ecc6 ("tcp: clamp route advmss to TCP_MIN_MSS")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv4/icmp.c                     |  2 +-
 net/ipv4/ip_output.c                |  4 ++--
 net/ipv4/ip_sockglue.c              |  2 +-
 net/ipv4/ipmr.c                     |  2 +-
 net/ipv4/netfilter/nf_reject_ipv4.c |  2 +-
 net/ipv4/tcp_ipv4.c                 | 13 ++++++-------
 net/ipv6/sit.c                      |  2 +-
 7 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 7c4c7b7fe3846..69cac8b20a217 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -785,7 +785,7 @@ void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info,
 
 	/* RFC says return as much as we can without exceeding 576 bytes. */
 
-	room = dst_mtu(&rt->dst);
+	room = dst4_mtu(&rt->dst);
 	if (room > 576)
 		room = 576;
 	room -= sizeof(struct iphdr) + icmp_param.replyopts.opt.opt.optlen;
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 150cdea8aacbe..9698290ef7293 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1304,7 +1304,7 @@ static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
 		return -EFAULT;
 
 	cork->fragsize = ip_sk_use_pmtu(sk) ?
-			 dst_mtu(&rt->dst) : READ_ONCE(rt->dst.dev->mtu);
+			 dst4_mtu(&rt->dst) : READ_ONCE(rt->dst.dev->mtu);
 
 	if (!inetdev_valid_mtu(cork->fragsize))
 		return -ENETUNREACH;
@@ -1438,7 +1438,7 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
 	 * locally. */
 	if (inet->pmtudisc == IP_PMTUDISC_DO ||
 	    inet->pmtudisc == IP_PMTUDISC_PROBE ||
-	    (skb->len <= dst_mtu(&rt->dst) &&
+	    (skb->len <= dst4_mtu(&rt->dst) &&
 	     ip_dont_fragment(sk, &rt->dst)))
 		df = htons(IP_DF);
 
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 1a6952921e07b..a5affb6e280ef 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -1642,7 +1642,7 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname,
 		val = 0;
 		dst = sk_dst_get(sk);
 		if (dst) {
-			val = dst_mtu(dst);
+			val = dst4_mtu(dst);
 			dst_release(dst);
 		}
 		if (!val) {
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index af9412a507cf3..074662e2daed6 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1895,7 +1895,7 @@ static void ipmr_queue_xmit(struct net *net, struct mr_table *mrt,
 
 	dev = rt->dst.dev;
 
-	if (skb->len+encap > dst_mtu(&rt->dst) && (ntohs(iph->frag_off) & IP_DF)) {
+	if (skb->len+encap > dst4_mtu(&rt->dst) && (ntohs(iph->frag_off) & IP_DF)) {
 		/* Do not fragment multicasts. Alas, IPv4 does not
 		 * allow to send ICMP, so that packets will disappear
 		 * to blackhole.
diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index 1632cedcd348c..76320f1ba4996 100644
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -296,7 +296,7 @@ void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
 		goto free_nskb;
 
 	/* "Never happens" */
-	if (nskb->len > dst_mtu(skb_dst(nskb)))
+	if (nskb->len > dst4_mtu(skb_dst(nskb)))
 		goto free_nskb;
 
 	nf_ct_attach(nskb, oldskb);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 3f9e1cfde0083..97e3ce3e60f98 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -363,7 +363,7 @@ void tcp_v4_mtu_reduced(struct sock *sk)
 {
 	struct inet_sock *inet = inet_sk(sk);
 	struct dst_entry *dst;
-	u32 mtu;
+	u32 mtu, dmtu;
 
 	if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
 		return;
@@ -375,15 +375,14 @@ void tcp_v4_mtu_reduced(struct sock *sk)
 	/* Something is about to be wrong... Remember soft error
 	 * for the case, if this connection will not able to recover.
 	 */
-	if (mtu < dst_mtu(dst) && ip_dont_fragment(sk, dst))
+	dmtu = dst4_mtu(dst);
+	if (mtu < dmtu && ip_dont_fragment(sk, dst))
 		WRITE_ONCE(sk->sk_err_soft, EMSGSIZE);
 
-	mtu = dst_mtu(dst);
-
 	if (inet->pmtudisc != IP_PMTUDISC_DONT &&
 	    ip_sk_accept_pmtu(sk) &&
-	    inet_csk(sk)->icsk_pmtu_cookie > mtu) {
-		tcp_sync_mss(sk, mtu);
+	    inet_csk(sk)->icsk_pmtu_cookie > dmtu) {
+		tcp_sync_mss(sk, dmtu);
 
 		/* Resend the TCP packet because it's
 		 * clear that the old packet has been
@@ -1624,7 +1623,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
 
 	tcp_ca_openreq_child(newsk, dst);
 
-	tcp_sync_mss(newsk, dst_mtu(dst));
+	tcp_sync_mss(newsk, dst4_mtu(dst));
 	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst));
 
 	tcp_initialize_rcv_mss(newsk);
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index ac38d4aa09ddc..b36fc57acf061 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -968,7 +968,7 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
 	iph6 = ipv6_hdr(skb);
 
 	if (df) {
-		mtu = dst_mtu(&rt->dst) - t_hlen;
+		mtu = dst4_mtu(&rt->dst) - t_hlen;
 
 		if (mtu < IPV4_MIN_MTU) {
 			DEV_STATS_INC(dev, collisions);
-- 
2.53.0

[PATCH 6.6.y 5/5] tcp: clamp route advmss to TCP_MIN_MSS

[Sasha Levin]

From: Yong Wang <edragain@163.com>

[ Upstream commit 870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1 ]

tcp_select_initial_window() assumes that callers never pass an MSS
smaller than 1, but route-derived advmss values can violate that
assumption.

A too-small explicit RTAX_ADVMSS is one way to get there, but it is not
the only one. The same divide-by-zero can also be reached through the
"default advmss" path when RTAX_ADVMSS is left at 0 and the effective
advmss is later driven down by route MTU and min_adv_mss.

Introduce a tcp_dst_advmss() helper that clamps route advmss to
TCP_MIN_MSS before TCP consumes it, and use it in the TCP paths that
derive advmss from dst metrics. This keeps the effective MSS from
dropping to zero before tcp_select_initial_window() rounds the receive
window.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Yong Wang <edragain@163.com>
Signed-off-by: Ren Wei <weir@nebusec.ai>
Link: https://patch.msgid.link/251eaf8277fa7c66364c9815c5da01662d269181.1787074852.git.edragain@163.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/net/tcp.h        | 5 +++++
 net/ipv4/tcp_ipv4.c      | 2 +-
 net/ipv4/tcp_minisocks.c | 2 +-
 net/ipv4/tcp_output.c    | 6 +++---
 net/ipv6/tcp_ipv6.c      | 2 +-
 5 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 23d830a7a6c82..8f411176b4180 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1475,6 +1475,11 @@ static inline int tcp_full_space(const struct sock *sk)
 	return tcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf));
 }
 
+static inline u32 tcp_dst_advmss(const struct dst_entry *dst)
+{
+	return max_t(u32, dst_metric_advmss(dst), TCP_MIN_MSS);
+}
+
 static inline void __tcp_adjust_rcv_ssthresh(struct sock *sk, u32 new_ssthresh)
 {
 	int unused_mem = sk_unused_reserved_mem(sk);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 97e3ce3e60f98..446e696fb31e7 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1624,7 +1624,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
 	tcp_ca_openreq_child(newsk, dst);
 
 	tcp_sync_mss(newsk, dst4_mtu(dst));
-	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst));
+	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), tcp_dst_advmss(dst));
 
 	tcp_initialize_rcv_mss(newsk);
 
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 86f0feb2497f1..c5df72b548955 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -403,7 +403,7 @@ void tcp_openreq_init_rwin(struct request_sock *req,
 	u32 rcv_wnd;
 	int mss;
 
-	mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
+	mss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
 	window_clamp = READ_ONCE(tp->window_clamp);
 	/* Set this up on the first call only */
 	req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 5abad93d3c743..67b88a962079f 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -125,7 +125,7 @@ static __u16 tcp_advertise_mss(struct sock *sk)
 	int mss = tp->advmss;
 
 	if (dst) {
-		unsigned int metric = dst_metric_advmss(dst);
+		unsigned int metric = tcp_dst_advmss(dst);
 
 		if (metric < mss) {
 			mss = metric;
@@ -3698,7 +3698,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
 	}
 	skb_dst_set(skb, dst);
 
-	mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
+	mss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
 
 	memset(&opts, 0, sizeof(opts));
 	now = tcp_clock_ns();
@@ -3810,7 +3810,7 @@ static void tcp_connect_init(struct sock *sk)
 
 	if (!tp->window_clamp)
 		WRITE_ONCE(tp->window_clamp, dst_metric(dst, RTAX_WINDOW));
-	tp->advmss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
+	tp->advmss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
 
 	tcp_initialize_rcv_mss(sk);
 
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 243d398c35868..4a6a0d95af150 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1341,7 +1341,7 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
 	tcp_ca_openreq_child(newsk, dst);
 
 	tcp_sync_mss(newsk, dst6_mtu(dst));
-	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst));
+	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), tcp_dst_advmss(dst));
 
 	tcp_initialize_rcv_mss(newsk);
 
-- 
2.53.0

Re: [PATCH 6.6.y 5/5] tcp: clamp route advmss to TCP_MIN_MSS

[Greg KH]

On Tue, Sep 01, 2026 at 10:18:04AM -0400, Sasha Levin wrote:
> From: Yong Wang <edragain@163.com>
> 
> [ Upstream commit 870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1 ]
> 
> tcp_select_initial_window() assumes that callers never pass an MSS
> smaller than 1, but route-derived advmss values can violate that
> assumption.
> 
> A too-small explicit RTAX_ADVMSS is one way to get there, but it is not
> the only one. The same divide-by-zero can also be reached through the
> "default advmss" path when RTAX_ADVMSS is left at 0 and the effective
> advmss is later driven down by route MTU and min_adv_mss.
> 
> Introduce a tcp_dst_advmss() helper that clamps route advmss to
> TCP_MIN_MSS before TCP consumes it, and use it in the TCP paths that
> derive advmss from dst metrics. This keeps the effective MSS from
> dropping to zero before tcp_select_initial_window() rounds the receive
> window.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Cc: stable@vger.kernel.org
> Reported-by: Vega <vega@nebusec.ai>
> Signed-off-by: Yong Wang <edragain@163.com>
> Signed-off-by: Ren Wei <weir@nebusec.ai>
> Link: https://patch.msgid.link/251eaf8277fa7c66364c9815c5da01662d269181.1787074852.git.edragain@163.com
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  include/net/tcp.h        | 5 +++++
>  net/ipv4/tcp_ipv4.c      | 2 +-
>  net/ipv4/tcp_minisocks.c | 2 +-
>  net/ipv4/tcp_output.c    | 6 +++---
>  net/ipv6/tcp_ipv6.c      | 2 +-
>  5 files changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 23d830a7a6c82..8f411176b4180 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -1475,6 +1475,11 @@ static inline int tcp_full_space(const struct sock *sk)
>  	return tcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf));
>  }
>  
> +static inline u32 tcp_dst_advmss(const struct dst_entry *dst)
> +{
> +	return max_t(u32, dst_metric_advmss(dst), TCP_MIN_MSS);
> +}
> +
>  static inline void __tcp_adjust_rcv_ssthresh(struct sock *sk, u32 new_ssthresh)
>  {
>  	int unused_mem = sk_unused_reserved_mem(sk);
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index 97e3ce3e60f98..446e696fb31e7 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1624,7 +1624,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
>  	tcp_ca_openreq_child(newsk, dst);
>  
>  	tcp_sync_mss(newsk, dst4_mtu(dst));
> -	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst));
> +	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), tcp_dst_advmss(dst));
>  
>  	tcp_initialize_rcv_mss(newsk);
>  
> diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> index 86f0feb2497f1..c5df72b548955 100644
> --- a/net/ipv4/tcp_minisocks.c
> +++ b/net/ipv4/tcp_minisocks.c
> @@ -403,7 +403,7 @@ void tcp_openreq_init_rwin(struct request_sock *req,
>  	u32 rcv_wnd;
>  	int mss;
>  
> -	mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
> +	mss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
>  	window_clamp = READ_ONCE(tp->window_clamp);
>  	/* Set this up on the first call only */
>  	req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 5abad93d3c743..67b88a962079f 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -125,7 +125,7 @@ static __u16 tcp_advertise_mss(struct sock *sk)
>  	int mss = tp->advmss;
>  
>  	if (dst) {
> -		unsigned int metric = dst_metric_advmss(dst);
> +		unsigned int metric = tcp_dst_advmss(dst);
>  
>  		if (metric < mss) {
>  			mss = metric;
> @@ -3698,7 +3698,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
>  	}
>  	skb_dst_set(skb, dst);
>  
> -	mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
> +	mss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
>  
>  	memset(&opts, 0, sizeof(opts));
>  	now = tcp_clock_ns();
> @@ -3810,7 +3810,7 @@ static void tcp_connect_init(struct sock *sk)
>  
>  	if (!tp->window_clamp)
>  		WRITE_ONCE(tp->window_clamp, dst_metric(dst, RTAX_WINDOW));
> -	tp->advmss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
> +	tp->advmss = tcp_mss_clamp(tp, tcp_dst_advmss(dst));
>  
>  	tcp_initialize_rcv_mss(sk);
>  
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index 243d398c35868..4a6a0d95af150 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -1341,7 +1341,7 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
>  	tcp_ca_openreq_child(newsk, dst);
>  
>  	tcp_sync_mss(newsk, dst6_mtu(dst));
> -	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst));
> +	newtp->advmss = tcp_mss_clamp(tcp_sk(sk), tcp_dst_advmss(dst));
>  
>  	tcp_initialize_rcv_mss(newsk);
>  
> -- 
> 2.53.0
> 
> 

did not apply