From 5a567d52f7b97b1f5e61604636bef555fdd84b8f Mon Sep 17 00:00:00 2001
From: yuanjm <yuanjianmin@espressif.com>
Date: Thu, 22 Apr 2021 14:47:18 +0800
Subject: [PATCH] dns: Fix server_idx increasing to DNS_MAX_SERVERS and trigger
 the LWIP_ASSERT

Closes https://github.com/espressif/esp-idf/issues/6878
---
 src/core/dns.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/core/dns.c b/src/core/dns.c
index fd1d420c..e758aca5 100644
--- a/src/core/dns.c
+++ b/src/core/dns.c
@@ -1089,8 +1089,8 @@ dns_check_entry(u8_t i)
       entry->tmr = 1;
       entry->retries = 0;
 #if ESP_DNS
-      while((entry->server_idx < DNS_MAX_SERVERS) && ip_addr_isany_val(dns_servers[entry->server_idx])) {
-        entry->server_idx++;
+      while((entry->server_idx + 1 < DNS_MAX_SERVERS) && ip_addr_isany_val(dns_servers[entry->server_idx])) {
+        entry->server_idx ++;
       }
 #endif
       /* send DNS packet for this entry */