From fc8ea40f6130ac18d9c66797de2cf1d5af55d496 Mon Sep 17 00:00:00 2001 From: Markus Theil 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 --- 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) @@ -480,9 +481,14 @@ 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; @@ -502,8 +508,20 @@ 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 @@ -9473,6 +9473,10 @@ 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)