This patch can also be left out, but then other measures should be taken,
to make most/all DFS channels available on each mesh point, in order for
channel switch and CSA to work so that network does not become disconnected/
partitioned.
On 6/30/20 2:19 PM, Markus Theil wrote:
> 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@xxxxxxxxxxxxx>
> ---
> src/ap/dfs.c | 20 +++++++++++++++++++-
> src/drivers/driver_nl80211.c | 4 ++++
> 2 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/src/ap/dfs.c b/src/ap/dfs.c
> index 25dad3482..8f3630bf8 100644
> --- 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_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;
> @@ -502,8 +508,20 @@ 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;
> dfs_find_channel(iface, &chan, chan_idx, skip_radar);
> if (!chan) {
> diff --git a/src/drivers/driver_nl80211.c b/src/drivers/driver_nl80211.c
> index d922eda74..18521f832 100644
> --- a/src/drivers/driver_nl80211.c
> +++ b/src/drivers/driver_nl80211.c
> @@ -9568,6 +9568,10 @@ 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)
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