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From fc8ea40f6130ac18d9c66797de2cf1d5af55d496 Mon Sep 17 00:00:00 2001
From: Markus Theil <markus.theil@tu-ilmenau.de>
Date: Tue, 30 Jun 2020 14:19:07 +0200
Subject: [PATCH 19/19] mesh: use deterministic channel on channel switch
This patch uses a deterministic channel on DFS channel switch
in mesh networks. Otherwise, when switching to a usable but not
available channel, no CSA can be sent and a random channel is choosen
without notification of other nodes. It is then quite likely, that
the mesh network gets disconnected.
Fix this by using a deterministic number, based on the sha256 hash
of the mesh ID, in order to use at least a different number in each
mesh network.
Signed-off-by: Markus Theil <markus.theil@tu-ilmenau.de>
---
src/ap/dfs.c | 20 +++++++++++++++++++-
src/drivers/driver_nl80211.c | 4 ++++
2 files changed, 23 insertions(+), 1 deletion(-)
--- a/src/ap/dfs.c
+++ b/src/ap/dfs.c
@@ -17,6 +17,7 @@
#include "ap_drv_ops.h"
#include "drivers/driver.h"
#include "dfs.h"
+#include "crypto/crypto.h"
static int dfs_get_used_n_chans(struct hostapd_iface *iface, int *seg1)
@@ -483,9 +484,14 @@ dfs_get_valid_channel(struct hostapd_ifa
int num_available_chandefs;
int chan_idx, chan_idx2;
int sec_chan_idx_80p80 = -1;
+ bool is_mesh = false;
int i;
u32 _rand;
+#ifdef CONFIG_MESH
+ is_mesh = iface->mconf;
+#endif
+
wpa_printf(MSG_DEBUG, "DFS: Selecting random channel");
*secondary_channel = 0;
*oper_centr_freq_seg0_idx = 0;
@@ -505,8 +511,20 @@ dfs_get_valid_channel(struct hostapd_ifa
if (num_available_chandefs == 0)
return NULL;
- if (os_get_random((u8 *) &_rand, sizeof(_rand)) < 0)
+ /* try to use deterministic channel in mesh, so that both sides
+ * have a chance to switch to the same channel */
+ if (is_mesh) {
+#ifdef CONFIG_MESH
+ u64 hash[4];
+ const u8 *meshid[1] = { &iface->mconf->meshid[0] };
+ const size_t meshid_len = iface->mconf->meshid_len;
+
+ sha256_vector(1, meshid, &meshid_len, (u8 *)&hash[0]);
+ _rand = hash[0] + hash[1] + hash[2] + hash[3];
+#endif
+ } else if (os_get_random((u8 *) &_rand, sizeof(_rand)) < 0)
return NULL;
+
chan_idx = _rand % num_available_chandefs;
dfs_find_channel(iface, &chan, chan_idx, skip_radar);
if (!chan) {
--- a/src/drivers/driver_nl80211.c
+++ b/src/drivers/driver_nl80211.c
@@ -9895,6 +9895,10 @@ static int nl80211_switch_channel(void *
if (ret)
goto error;
+ if (drv->nlmode == NL80211_IFTYPE_MESH_POINT) {
+ nla_put_flag(msg, NL80211_ATTR_HANDLE_DFS);
+ }
+
/* beacon_csa params */
beacon_csa = nla_nest_start(msg, NL80211_ATTR_CSA_IES);
if (!beacon_csa)
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