From c028c6309a9f9b385ba8c0c984eb2b6c3f368650 Mon Sep 17 00:00:00 2001
From: Johannes Berg <johannes.berg@intel.com>
Date: Tue, 30 Jan 2018 13:17:38 +0100
Subject: [PATCH] cfg80211: use only 1Mbps for basic rates in mesh
Git-commit: c028c6309a9f9b385ba8c0c984eb2b6c3f368650
Patch-mainline: v4.16-rc3
References: FATE#326294

Mesh used to use the mandatory rates as basic rates, but we got
the calculation of mandatory rates wrong until some time ago.
Fix this this broke interoperability with older versions since
now more basic rates are required, and thus the MBSS isn't the
same and the network stops working.

Fix this by simply using only 1Mbps as the basic rate in 2.4GHz.
Since the changed mandatory rates only affected 2.4GHz, this is
all we need to make it work again.

Reported-and-tested-by: Matthias Schiffer <mschiffer@universe-factory.net>
Fixes: 1bd773c077de ("wireless: set correct mandatory rate flags")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 net/wireless/mesh.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/net/wireless/mesh.c b/net/wireless/mesh.c
index 51aa55618ef7..b12da6ef3c12 100644
--- a/net/wireless/mesh.c
+++ b/net/wireless/mesh.c
@@ -170,9 +170,28 @@ int __cfg80211_join_mesh(struct cfg80211_registered_device *rdev,
 		enum nl80211_bss_scan_width scan_width;
 		struct ieee80211_supported_band *sband =
 				rdev->wiphy.bands[setup->chandef.chan->band];
-		scan_width = cfg80211_chandef_to_scan_width(&setup->chandef);
-		setup->basic_rates = ieee80211_mandatory_rates(sband,
-							       scan_width);
+
+		if (setup->chandef.chan->band == NL80211_BAND_2GHZ) {
+			int i;
+
+			/*
+			 * Older versions selected the mandatory rates for
+			 * 2.4 GHz as well, but were broken in that only
+			 * 1 Mbps was regarded as a mandatory rate. Keep
+			 * using just 1 Mbps as the default basic rate for
+			 * mesh to be interoperable with older versions.
+			 */
+			for (i = 0; i < sband->n_bitrates; i++) {
+				if (sband->bitrates[i].bitrate == 10) {
+					setup->basic_rates = BIT(i);
+					break;
+				}
+			}
+		} else {
+			scan_width = cfg80211_chandef_to_scan_width(&setup->chandef);
+			setup->basic_rates = ieee80211_mandatory_rates(sband,
+								       scan_width);
+		}
 	}
 
 	err = cfg80211_chandef_dfs_required(&rdev->wiphy,
-- 
2.19.2