From: Daniel Stenberg <daniel@haxx.se>
Date: Thu, 9 Oct 2025 07:07:27 +0000 (+0200)
Subject: hostip: don't store negative resolves due unrelated errors
X-Git-Tag: rc-8_17_0-1~40
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=b0db5f12b15aeaa7eec42463ff26c2c59898f3ab;p=thirdparty%2Fcurl.git

hostip: don't store negative resolves due unrelated errors

Like for:

- OOM
- resolver_start() returns error
- DoH has problems

Fixes #18953
Fixes #18954
Reported-by: Joshua Rogers
Closes #18958
---

diff --git a/lib/hostip.c b/lib/hostip.c
index ceea189732..a6531c3171 100644
--- a/lib/hostip.c
+++ b/lib/hostip.c
@@ -846,6 +846,7 @@ CURLcode Curl_resolv(struct Curl_easy *data,
   int respwait = 0;
   bool is_ipaddr;
   size_t hostname_len;
+  bool keep_negative = TRUE; /* cache a negative result */
 
 #ifndef CURL_DISABLE_DOH
   data->conn->bits.doh = FALSE; /* default is not */
@@ -887,8 +888,10 @@ CURLcode Curl_resolv(struct Curl_easy *data,
     st = data->set.resolver_start(resolver, NULL,
                                   data->set.resolver_start_client);
     Curl_set_in_callback(data, FALSE);
-    if(st)
+    if(st) {
+      keep_negative = FALSE;
       goto error;
+    }
   }
 
   /* shortcut literal IP addresses, if we are not told to resolve them. */
@@ -947,10 +950,11 @@ out:
   else if(addr) {
     /* we got a response, create a dns entry, add to cache, return */
     dns = Curl_dnscache_mk_entry(data, addr, hostname, 0, port, FALSE);
-    if(!dns)
-      goto error;
-    if(Curl_dnscache_add(data, dns))
+    if(!dns || Curl_dnscache_add(data, dns)) {
+      /* this is OOM or similar, don't store such negative resolves */
+      keep_negative = FALSE;
       goto error;
+    }
     show_resolve_info(data, dns);
     *entry = dns;
     return CURLE_OK;
@@ -966,7 +970,8 @@ error:
     Curl_resolv_unlink(data, &dns);
   *entry = NULL;
   Curl_async_shutdown(data);
-  store_negative_resolve(data, hostname, port);
+  if(keep_negative)
+    store_negative_resolve(data, hostname, port);
   return CURLE_COULDNT_RESOLVE_HOST;
 }
 
@@ -1550,7 +1555,8 @@ CURLcode Curl_resolv_check(struct Curl_easy *data,
   result = Curl_async_is_resolved(data, dns);
   if(*dns)
     show_resolve_info(data, *dns);
-  if(result)
+  if((result == CURLE_COULDNT_RESOLVE_HOST) ||
+     (result == CURLE_COULDNT_RESOLVE_PROXY))
     store_negative_resolve(data, data->state.async.hostname,
                            data->state.async.port);
   return result;