From 79f5962baea74ce1cd4e5949598944bff854b166 Mon Sep 17 00:00:00 2001 From: Johan Almbladh Date: Mon, 28 Jun 2021 14:32:46 +0200 Subject: mac80211: Fix monitor MTU limit so that A-MSDUs get through The maximum MTU was set to 2304, which is the maximum MSDU size. While this is valid for normal WLAN interfaces, it is too low for monitor interfaces. A monitor interface may receive and inject MPDU frames, and the maximum MPDU frame size is larger than 2304. The MPDU may also contain an A-MSDU frame, in which case the size may be much larger than the MTU limit. Since the maximum size of an A-MSDU depends on the PHY mode of the transmitting STA, it is not possible to set an exact MTU limit for a monitor interface. Now the maximum MTU for a monitor interface is unrestricted. Signed-off-by: Johan Almbladh Link: https://lore.kernel.org/r/20210628123246.2070558-1-johan.almbladh@anyfinetworks.com Signed-off-by: Johannes Berg --- net/mac80211/iface.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) (limited to 'net/mac80211') diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c index 1e5e9fc45523..cd96cd337aa8 100644 --- a/net/mac80211/iface.c +++ b/net/mac80211/iface.c @@ -2001,9 +2001,16 @@ int ieee80211_if_add(struct ieee80211_local *local, const char *name, netdev_set_default_ethtool_ops(ndev, &ieee80211_ethtool_ops); - /* MTU range: 256 - 2304 */ + /* MTU range is normally 256 - 2304, where the upper limit is + * the maximum MSDU size. Monitor interfaces send and receive + * MPDU and A-MSDU frames which may be much larger so we do + * not impose an upper limit in that case. + */ ndev->min_mtu = 256; - ndev->max_mtu = local->hw.max_mtu; + if (type == NL80211_IFTYPE_MONITOR) + ndev->max_mtu = 0; + else + ndev->max_mtu = local->hw.max_mtu; ret = cfg80211_register_netdevice(ndev); if (ret) { -- cgit v1.2.3