P2P: Avoid unsafe pre-configured channel as channel preference

Do not select pre-configured channel as operating channel preference if
it is unavailable maybe due to interference or possible known
co-existence constraints, and try to select random available channel.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

src/p2p/p2p.c

@@ -1208,10 +1208,51 @@ static void p2p_prepare_channel_best(struct p2p_data *p2p)
 		   0) {
 		p2p_dbg(p2p, "Select possible 5 GHz channel (op_class %u channel %u) as operating channel preference",
 			p2p->op_reg_class, p2p->op_channel);
-	} else {
+	} else if (p2p_channels_includes(&p2p->cfg->channels,
+					 p2p->cfg->op_reg_class,
+					 p2p->cfg->op_channel)) {
 		p2p_dbg(p2p, "Select pre-configured channel as operating channel preference");
 		p2p->op_reg_class = p2p->cfg->op_reg_class;
 		p2p->op_channel = p2p->cfg->op_channel;
+	} else {
+		u8 op_chans[3];
+		u8 *op_chan;
+		size_t num_channels = 0;
+		unsigned int r;
+
+		/* Try to find available social channels from 2.4 GHz */
+		if (p2p_channels_includes(&p2p->cfg->channels, 81, 1))
+			op_chans[num_channels++] = 1;
+		if (p2p_channels_includes(&p2p->cfg->channels, 81, 6))
+			op_chans[num_channels++] = 6;
+		if (p2p_channels_includes(&p2p->cfg->channels, 81, 11))
+			op_chans[num_channels++] = 11;
+
+		if (num_channels) {
+			p2p_dbg(p2p, "Select random available social channel from 2.4 GHz band as operating channel preference");
+			op_chan = op_chans;
+		} else {
+			struct p2p_reg_class *class;
+
+			/* Select any random available channel from the first
+			 * operating class */
+			p2p_dbg(p2p, "Select random available channel from operating class %d as operating channel preference",
+				p2p->op_reg_class);
+			class = &p2p->cfg->channels.reg_class[0];
+			p2p->op_reg_class = class->reg_class;
+			op_chan = &class->channel[0];
+			num_channels = class->channels;
+			if (num_channels == 0) {
+				/* Should not happen, but make sure we do not
+				 * try to divide by zero */
+				op_chan = op_chans;
+				op_chans[0] = 1;
+				num_channels = 1;
+			}
+		}
+		os_get_random((u8 *) &r, sizeof(r));
+		r %= num_channels;
+		p2p->op_channel = op_chan[r];
 	}
 
 	os_memcpy(&p2p->channels, &p2p->cfg->channels,