From 213d696db0cd951311cc6e8535fc76f2dd508146 Mon Sep 17 00:00:00 2001
From: Claire Wang <clairew@users.noreply.github.com>
Date: Fri, 19 Jan 2024 20:04:22 -0500
Subject: [PATCH] magicsock: mute noisy expected peer mtu related error
 (#10870)

---
 wgengine/magicsock/magicsock.go     |  2 +-
 wgengine/magicsock/peermtu.go       | 20 +++++++++++++++++++-
 wgengine/magicsock/peermtu_stubs.go |  6 ++++++
 3 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/wgengine/magicsock/magicsock.go b/wgengine/magicsock/magicsock.go
index 0d1a15a22..edc812b48 100644
--- a/wgengine/magicsock/magicsock.go
+++ b/wgengine/magicsock/magicsock.go
@@ -1317,7 +1317,7 @@ func (c *Conn) sendDiscoMessage(dst netip.AddrPort, dstKey key.NodePublic, dstDi
 	} else if err == nil {
 		// Can't send. (e.g. no IPv6 locally)
 	} else {
-		if !c.networkDown() {
+		if !c.networkDown() && pmtuShouldLogDiscoTxErr(m, err) {
 			c.logf("magicsock: disco: failed to send %v to %v: %v", disco.MessageSummary(m), dst, err)
 		}
 	}
diff --git a/wgengine/magicsock/peermtu.go b/wgengine/magicsock/peermtu.go
index 199585323..b675bf409 100644
--- a/wgengine/magicsock/peermtu.go
+++ b/wgengine/magicsock/peermtu.go
@@ -5,7 +5,13 @@
 
 package magicsock
 
-import "tailscale.com/net/tstun"
+import (
+	"errors"
+
+	"golang.org/x/sys/unix"
+	"tailscale.com/disco"
+	"tailscale.com/net/tstun"
+)
 
 // Peer path MTU routines shared by platforms that implement it.
 
@@ -110,3 +116,15 @@ func (c *Conn) UpdatePMTUD() {
 	c.peerMTUEnabled.Store(newStatus)
 	c.resetEndpointStates()
 }
+
+var errEMSGSIZE error = unix.EMSGSIZE
+
+func pmtuShouldLogDiscoTxErr(m disco.Message, err error) bool {
+	// Large disco.Ping packets used to probe path MTU may result in
+	// an EMSGSIZE error fairly regularly which can pollute logs.
+	p, ok := m.(*disco.Ping)
+	if !ok || p.Padding == 0 || !errors.Is(err, errEMSGSIZE) || debugPMTUD() {
+		return true
+	}
+	return false
+}
diff --git a/wgengine/magicsock/peermtu_stubs.go b/wgengine/magicsock/peermtu_stubs.go
index 4675e2501..e4f8038a4 100644
--- a/wgengine/magicsock/peermtu_stubs.go
+++ b/wgengine/magicsock/peermtu_stubs.go
@@ -5,6 +5,8 @@
 
 package magicsock
 
+import "tailscale.com/disco"
+
 func (c *Conn) DontFragSetting() (bool, error) {
 	return false, nil
 }
@@ -19,3 +21,7 @@ func (c *Conn) PeerMTUEnabled() bool {
 
 func (c *Conn) UpdatePMTUD() {
 }
+
+func pmtuShouldLogDiscoTxErr(m disco.Message, err error) bool {
+	return true
+}