* FAILED: patch "[PATCH] tcp: clamp route advmss to TCP_MIN_MSS" failed to apply to 5.15-stable tree
@ 2026-08-31 12:53 gregkh
2026-09-01 22:21 ` [PATCH 5.15.y 1/4] inet: add dst4_mtu() and dst6_mtu() helpers Sasha Levin
0 siblings, 1 reply; 5+ messages in thread
From: gregkh @ 2026-08-31 12:53 UTC (permalink / raw)
To: edragain, kuba, vega, weir; +Cc: stable
The patch below does not apply to the 5.15-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-5.15.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 '2026083106-sterile-daunting-b716@gregkh' --subject-prefix 'PATCH 5.15.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);
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH 5.15.y 1/4] inet: add dst4_mtu() and dst6_mtu() helpers
2026-08-31 12:53 FAILED: patch "[PATCH] tcp: clamp route advmss to TCP_MIN_MSS" failed to apply to 5.15-stable tree gregkh
@ 2026-09-01 22:21 ` Sasha Levin
2026-09-01 22:21 ` [PATCH 5.15.y 2/4] ipv6: use dst6_mtu() instead of dst_mtu() Sasha Levin
` (2 more replies)
0 siblings, 3 replies; 5+ messages in thread
From: Sasha Levin @ 2026-09-01 22:21 UTC (permalink / raw)
To: stable; +Cc: Eric Dumazet, Kuniyuki Iwashima, Jakub Kicinski, 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 9a23986f1071a..9adea166d2d97 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -201,6 +201,12 @@ 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 5efd0b71dc673..299d964850fd3 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -263,6 +263,12 @@ 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(struct sk_buff *skb)
{
unsigned int mtu;
--
2.53.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH 5.15.y 2/4] ipv6: use dst6_mtu() instead of dst_mtu()
2026-09-01 22:21 ` [PATCH 5.15.y 1/4] inet: add dst4_mtu() and dst6_mtu() helpers Sasha Levin
@ 2026-09-01 22:21 ` Sasha Levin
2026-09-01 22:21 ` [PATCH 5.15.y 3/4] ipv4: use dst4_mtu() " Sasha Levin
2026-09-01 22:21 ` [PATCH 5.15.y 4/4] tcp: clamp route advmss to TCP_MIN_MSS Sasha Levin
2 siblings, 0 replies; 5+ messages in thread
From: Sasha Levin @ 2026-09-01 22:21 UTC (permalink / raw)
To: stable; +Cc: Eric Dumazet, Kuniyuki Iwashima, Jakub Kicinski, 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 f9c088cc94395..3ad4edba5f32b 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 ab745cda1179b..1dbcd79dd9bb0 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -323,7 +323,7 @@ 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_UPD_PO_STATS(net, idev, IPSTATS_MIB_OUT, skb->len);
@@ -1364,10 +1364,10 @@ 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 45e0cec505c26..9f4c71889d911 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -643,7 +643,7 @@ 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);
@@ -1185,7 +1185,7 @@ 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 41e8b02c12c83..3d598d7fde1f8 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -1210,7 +1210,7 @@ static 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;
@@ -1309,7 +1309,7 @@ static 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 43b8995142e2e..63e8435c4b82f 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1990,6 +1990,8 @@ 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.
@@ -2000,10 +2002,10 @@ 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;
@@ -2867,7 +2869,7 @@ 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)) {
@@ -3184,7 +3186,7 @@ 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 dea59b123eb75..5c6b0d98730d9 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -354,7 +354,7 @@ 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;
@@ -371,8 +371,9 @@ 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);
}
}
@@ -1394,7 +1395,7 @@ 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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH 5.15.y 3/4] ipv4: use dst4_mtu() instead of dst_mtu()
2026-09-01 22:21 ` [PATCH 5.15.y 1/4] inet: add dst4_mtu() and dst6_mtu() helpers Sasha Levin
2026-09-01 22:21 ` [PATCH 5.15.y 2/4] ipv6: use dst6_mtu() instead of dst_mtu() Sasha Levin
@ 2026-09-01 22:21 ` Sasha Levin
2026-09-01 22:21 ` [PATCH 5.15.y 4/4] tcp: clamp route advmss to TCP_MIN_MSS Sasha Levin
2 siblings, 0 replies; 5+ messages in thread
From: Sasha Levin @ 2026-09-01 22:21 UTC (permalink / raw)
To: stable; +Cc: Eric Dumazet, Kuniyuki Iwashima, Jakub Kicinski, 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>
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 49c94aebac32d..b1812362f0965 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -768,7 +768,7 @@ 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 fb64f5fcc422f..ffa8d6363a820 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1262,7 +1262,7 @@ 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;
@@ -1528,7 +1528,7 @@ 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 3620dc739a5bf..f985d9a0dcdac 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -1631,7 +1631,7 @@ static 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 5e582eab1ea19..1a9d499d914bf 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1860,7 +1860,7 @@ 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 fbd264aa0a7ec..f64552b2cb832 100644
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -298,7 +298,7 @@ void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
niph = ip_hdr(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 f7693166c5161..6f97dfbc5343d 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -352,7 +352,7 @@ 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;
@@ -364,15 +364,14 @@ 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
@@ -1614,7 +1613,7 @@ 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 4b16ddc3d6c7f..3f8e03cded539 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -974,7 +974,7 @@ 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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH 5.15.y 4/4] tcp: clamp route advmss to TCP_MIN_MSS
2026-09-01 22:21 ` [PATCH 5.15.y 1/4] inet: add dst4_mtu() and dst6_mtu() helpers Sasha Levin
2026-09-01 22:21 ` [PATCH 5.15.y 2/4] ipv6: use dst6_mtu() instead of dst_mtu() Sasha Levin
2026-09-01 22:21 ` [PATCH 5.15.y 3/4] ipv4: use dst4_mtu() " Sasha Levin
@ 2026-09-01 22:21 ` Sasha Levin
2 siblings, 0 replies; 5+ messages in thread
From: Sasha Levin @ 2026-09-01 22:21 UTC (permalink / raw)
To: stable; +Cc: Yong Wang, Vega, Ren Wei, Jakub Kicinski, 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>
[ discarded upstream ssthresh refactor context and kept existing WRITE_ONCE-free window_clamp assignment style, replacing dst_metric_advmss() with tcp_dst_advmss() ]
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 be91d81d66ab3..48e0a1d363e84 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1436,6 +1436,11 @@ 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);
+}
+
void tcp_cleanup_rbuf(struct sock *sk, int copied);
/* We provision sk_rcvbuf around 200% of sk_rcvlowat.
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 6f97dfbc5343d..dac9c151f671b 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1614,7 +1614,7 @@ 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 061225d645e6b..e36c466b4b65a 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -369,7 +369,7 @@ 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 a2d5e9f1fe241..462c704cc18a9 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;
@@ -3597,7 +3597,7 @@ 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();
@@ -3713,7 +3713,7 @@ static void tcp_connect_init(struct sock *sk)
if (!tp->window_clamp)
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 5c6b0d98730d9..7dc0d53c3c249 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1396,7 +1396,7 @@ 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
^ permalink raw reply related [flat|nested] 5+ messages in thread
end of thread, other threads:[~2026-09-01 22:21 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-08-31 12:53 FAILED: patch "[PATCH] tcp: clamp route advmss to TCP_MIN_MSS" failed to apply to 5.15-stable tree gregkh
2026-09-01 22:21 ` [PATCH 5.15.y 1/4] inet: add dst4_mtu() and dst6_mtu() helpers Sasha Levin
2026-09-01 22:21 ` [PATCH 5.15.y 2/4] ipv6: use dst6_mtu() instead of dst_mtu() Sasha Levin
2026-09-01 22:21 ` [PATCH 5.15.y 3/4] ipv4: use dst4_mtu() " Sasha Levin
2026-09-01 22:21 ` [PATCH 5.15.y 4/4] tcp: clamp route advmss to TCP_MIN_MSS Sasha Levin
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.