nm-device: avoid improper IPv6 MTU configurationlr/ipv6-mtu-rh1194007

Ensure it's always (before address configuration starts and on updates) >= 1280
and not higher than the device MTU.

1 files changed, 49 insertions, 4 deletions

diff --git a/src/devices/nm-device.c b/src/devices/nm-device.c
index 808ba6f0b1..c31b47667b 100644
--- a/src/devices/nm-device.c
+++ b/src/devices/nm-device.c
@@ -464,6 +464,12 @@ nm_device_ipv6_sysctl_set (NMDevice *self, const char *property, const char *val
 	return nm_platform_sysctl_set (nm_utils_ip6_property_path (nm_device_get_ip_iface (self), property), value);
 }
 
+static guint32
+nm_device_ipv6_sysctl_get_int32 (NMDevice *self, const char *property, gint32 fallback)
+{
+	return nm_platform_sysctl_get_int32 (nm_utils_ip6_property_path (nm_device_get_ip_iface (self), property), fallback);
+}
+
 static gboolean
 device_has_capability (NMDevice *self, NMDeviceCapabilities caps)
 {
@@ -4079,21 +4085,53 @@ print_support_extended_ifa_flags (NMSettingIP6ConfigPrivacy use_tempaddr)
 	warn = 2;
 }
 
+static void nm_device_ipv6_set_mtu (NMDevice *self, guint32 mtu);
+
 static void
 nm_device_set_mtu (NMDevice *self, guint32 mtu)
 {
-        /* MTU */
-        if (mtu && mtu != nm_platform_link_get_mtu (ifindex))
-                nm_platform_link_set_mtu (ifindex, mtu);
+	NMDevicePrivate *priv = NM_DEVICE_GET_PRIVATE (self);
+	int ifindex = nm_device_get_ifindex (self);
+
+	if (mtu)
+		priv->mtu = mtu;
+
+	/* Ensure the IPv6 MTU is still alright. */
+	if (priv->ip6_mtu)
+		nm_device_ipv6_set_mtu (self, priv->ip6_mtu);
+
+	if (priv->mtu != nm_platform_link_get_mtu (ifindex))
+		nm_platform_link_set_mtu (ifindex, priv->mtu);
 }
 
 static void
 nm_device_ipv6_set_mtu (NMDevice *self, guint32 mtu)
 {
 	NMDevicePrivate *priv = NM_DEVICE_GET_PRIVATE (self);
+	guint32 plat_mtu = nm_device_ipv6_sysctl_get_int32 (self, "mtu", priv->mtu);
 	char val[16];
 
-	if (mtu) {
+	priv->ip6_mtu = mtu ?: plat_mtu;
+
+	if (priv->ip6_mtu && priv->mtu < priv->ip6_mtu) {
+		_LOGW (LOGD_DEVICE | LOGD_IP6, "Lowering IPv6 MTU (%d) to match device MTU (%d)",
+		       priv->ip6_mtu, priv->mtu);
+		priv->ip6_mtu = priv->mtu;
+	}
+
+	if (priv->ip6_mtu < 1280) {
+		_LOGW (LOGD_DEVICE | LOGD_IP6, "IPv6 MTU (%d) smaller than 1280, adjusting",
+		       priv->ip6_mtu);
+		priv->ip6_mtu = 1280;
+	}
+
+	if (priv->mtu < priv->ip6_mtu) {
+		_LOGW (LOGD_DEVICE | LOGD_IP6, "Raising device MTU (%d) to match IPv6 MTU (%d)",
+		       priv->mtu, priv->ip6_mtu);
+		nm_device_set_mtu (self, priv->ip6_mtu);
+	}
+
+	if (priv->ip6_mtu != plat_mtu) {
 		g_snprintf (val, sizeof (val), "%d", mtu);
 		nm_device_ipv6_sysctl_set (self, "mtu", val);
 	}
@@ -4598,6 +4636,13 @@ act_stage3_ip6_config_start (NMDevice *self,
 		return NM_ACT_STAGE_RETURN_STOP;
 	}
 
+	/* Ensure the MTU makes sense. If it was below 1280 the kernel would not
+	 * expose any ipv6 sysctls or allow presence of any addresses on the interface,
+	 * including LL, which * would make it impossible to autoconfigure MTU to a
+	 * correct value. */
+	if (!nm_device_uses_assumed_connection (self))
+		nm_device_ipv6_set_mtu (self, priv->ip6_mtu);
+
 	/* Any method past this point requires an IPv6LL address. Use NM-controlled
 	 * IPv6LL if this is not an assumed connection, since assumed connections
 	 * will already have IPv6 set up.