staging: rtl8723bs: Use scnprintf() for avoiding potential buffer overflow

Since snprintf() returns the would-be-output size instead of the
actual output size, the succeeding calls may go beyond the given
buffer limit.  Fix it by replacing with scnprintf().
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20200311092451.23933-4-tiwai@suse.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/core/rtw_wlan_util.c

@@ -326,20 +326,20 @@ inline void rtw_set_oper_ch(struct adapter *adapter, u8 ch)
 		dvobj->on_oper_ch_time = jiffies;
 
 #ifdef DBG_CH_SWITCH
-		cnt += snprintf(msg+cnt, len-cnt, "switch to ch %3u", ch);
+		cnt += scnprintf(msg+cnt, len-cnt, "switch to ch %3u", ch);
 
 		for (i = 0; i < dvobj->iface_nums; i++) {
 			struct adapter *iface = dvobj->padapters[i];
-			cnt += snprintf(msg+cnt, len-cnt, " ["ADPT_FMT":", ADPT_ARG(iface));
+			cnt += scnprintf(msg+cnt, len-cnt, " ["ADPT_FMT":", ADPT_ARG(iface));
 			if (iface->mlmeextpriv.cur_channel == ch)
-				cnt += snprintf(msg+cnt, len-cnt, "C");
+				cnt += scnprintf(msg+cnt, len-cnt, "C");
 			else
-				cnt += snprintf(msg+cnt, len-cnt, "_");
+				cnt += scnprintf(msg+cnt, len-cnt, "_");
 			if (iface->wdinfo.listen_channel == ch && !rtw_p2p_chk_state(&iface->wdinfo, P2P_STATE_NONE))
-				cnt += snprintf(msg+cnt, len-cnt, "L");
+				cnt += scnprintf(msg+cnt, len-cnt, "L");
 			else
-				cnt += snprintf(msg+cnt, len-cnt, "_");
-			cnt += snprintf(msg+cnt, len-cnt, "]");
+				cnt += scnprintf(msg+cnt, len-cnt, "_");
+			cnt += scnprintf(msg+cnt, len-cnt, "]");
 		}
 
 		DBG_871X(FUNC_ADPT_FMT" %s\n", FUNC_ADPT_ARG(adapter), msg);

drivers/staging/rtl8723bs/os_dep/ioctl_linux.c

@@ -197,12 +197,12 @@ static char *translate_scan(struct adapter *padapter,
 	if (!custom)
 		return start;
 	p = custom;
-	p += snprintf(p, MAX_CUSTOM_LEN - (p - custom), " Rates (Mb/s): ");
+	p += scnprintf(p, MAX_CUSTOM_LEN - (p - custom), " Rates (Mb/s): ");
 	while (pnetwork->network.SupportedRates[i] != 0) {
 		rate = pnetwork->network.SupportedRates[i]&0x7F;
 		if (rate > max_rate)
 			max_rate = rate;
-		p += snprintf(p, MAX_CUSTOM_LEN - (p - custom),
+		p += scnprintf(p, MAX_CUSTOM_LEN - (p - custom),
 			      "%d%s ", rate >> 1, (rate & 1) ? ".5" : "");
 		i++;
 	}