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mesh: use deterministic channel on channel switch

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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>
This commit is contained in:
Markus Theil 2020-06-30 14:19:07 +02:00 • committed by sinavir
parent 945aea6ff0
commit 72573cdb95
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2 changed files with 23 additions and 1 deletions
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20
src/ap/dfs.c
View file

@ -18,6 +18,7 @@
#include "ap_drv_ops.h"
#include "drivers/driver.h"
#include "dfs.h"
#include "crypto/crypto.h"
enum dfs_channel_type {
@ -534,9 +535,14 @@ dfs_get_valid_channel(struct hostapd_iface *iface,
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;
@ -556,8 +562,20 @@ dfs_get_valid_channel(struct hostapd_iface *iface,
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;
wpa_printf(MSG_DEBUG, "DFS: Picked random entry from the list: %d/%d",
chan_idx, num_available_chandefs);

4
src/drivers/driver_nl80211.c
View file

@ -11465,6 +11465,10 @@ static int nl80211_switch_channel(void *priv, struct csa_settings *settings)
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)