From 7af6c0ef6354288f8a8240e5ca44a55ab4c6cf91 Mon Sep 17 00:00:00 2001
From: Alexey Tikhonov <atikhono@redhat.com>
Date: Thu, 15 Jun 2023 18:04:50 +0200
Subject: [PATCH] 
 https://github.com/c-ares/c-ares/commit/b9b8413cfdb70a3f99e1573333b23052d57ec1ae

---
 ares_process.c | 41 ++++++++++++++++++++++++-----------------
 1 file changed, 24 insertions(+), 17 deletions(-)

diff --git a/ares_process.c b/ares_process.c
index bbeca5e..ad7e862 100644
--- a/ares_process.c
+++ b/ares_process.c
@@ -416,7 +416,7 @@ static void read_udp_packets(ares_channel channel, fd_set *read_fds,
 {
   struct server_state *server;
   int i;
-  ssize_t count;
+  ssize_t read_len;
   unsigned char buf[MAXENDSSZ + 1];
 #ifdef HAVE_RECVFROM
   ares_socklen_t fromlen;
@@ -459,36 +459,43 @@ static void read_udp_packets(ares_channel channel, fd_set *read_fds,
       /* To reduce event loop overhead, read and process as many
        * packets as we can. */
       do {
-        if (server->udp_socket == ARES_SOCKET_BAD)
-          count = 0;
-
-        else {
+        if (server->udp_socket == ARES_SOCKET_BAD) {
+          read_len = -1;
+        } else {
 #ifdef HAVE_RECVFROM
-          if (server->addr.family == AF_INET)
+          if (server->addr.family == AF_INET) {
             fromlen = sizeof(from.sa4);
-          else
+          } else {
             fromlen = sizeof(from.sa6);
-          count = (ssize_t)recvfrom(server->udp_socket, (void *)buf,
-                                    sizeof(buf), 0, &from.sa, &fromlen);
+          }
+          read_len = (ssize_t)recvfrom(server->udp_socket, (void *)buf,
+                                       sizeof(buf), 0, &from.sa, &fromlen);
 #else
-          count = sread(server->udp_socket, buf, sizeof(buf));
+          read_len = sread(server->udp_socket, buf, sizeof(buf));
 #endif
         }
 
-        if (count == -1 && try_again(SOCKERRNO))
+        if (read_len == 0) {
+          /* UDP is connectionless, so result code of 0 is a 0-length UDP
+           * packet, and not an indication the connection is closed like on
+           * tcp */
           continue;
-        else if (count <= 0)
+        } else if (read_len < 0) {
+          if (try_again(SOCKERRNO))
+            continue;
+
           handle_error(channel, i, now);
 #ifdef HAVE_RECVFROM
-        else if (!same_address(&from.sa, &server->addr))
+        } else if (!same_address(&from.sa, &server->addr)) {
           /* The address the response comes from does not match the address we
            * sent the request to. Someone may be attempting to perform a cache
            * poisoning attack. */
-          break;
+          continue;
 #endif
-        else
-          process_answer(channel, buf, (int)count, i, 0, now);
-       } while (count > 0);
+        } else {
+          process_answer(channel, buf, (int)read_len, i, 0, now);
+        }
+      } while (read_len >= 0);
     }
 }
 
-- 
2.38.1