resolve: don't leak pre-populated dns entries

CURLOPT_RESOLVE populates the DNS cache with entries that are marked as
eternally in use. Those entries need to be taken care of when the cache
is killed off.

Bug: http://curl.haxx.se/bug/view.cgi?id=3463121
Reported by: "tw84452852"

3 files changed, 29 insertions, 12 deletions

diff --git a/lib/hostip.c b/lib/hostip.c
index d261a163a..44ed0a424 100644
--- a/lib/hostip.c
+++ b/lib/hostip.c
@@ -721,4 +721,25 @@ struct curl_hash *Curl_mk_dnscache(void)
   return Curl_hash_alloc(7, Curl_hash_str, Curl_str_key_compare, freednsentry);
 }
 
+static int hostcache_inuse(void *data, void *hc)
+{
+  struct Curl_dns_entry *c = (struct Curl_dns_entry *) hc;
+
+  if(c->inuse == 1)
+    Curl_resolv_unlock(data, c);
+
+  return 1; /* free all entries */
+}
 
+void Curl_hostcache_destroy(struct SessionHandle *data)
+{
+  /* Entries added to the hostcache with the CURLOPT_RESOLVE function are
+   * still present in the cache with the inuse counter set to 1. Detect them
+   * and cleanup!
+   */
+  Curl_hash_clean_with_criterium(data->dns.hostcache, data, hostcache_inuse);
+
+  Curl_hash_destroy(data->dns.hostcache);
+  data->dns.hostcachetype = HCACHE_NONE;
+  data->dns.hostcache = NULL;
+}
diff --git a/lib/hostip.h b/lib/hostip.h
index dbbb1f7a2..100bdc58e 100644
--- a/lib/hostip.h
+++ b/lib/hostip.h
@@ -200,4 +200,9 @@ extern sigjmp_buf curl_jmpenv;
  */
 CURLcode Curl_set_dns_servers(struct SessionHandle *data, char *servers);
 
+/*
+ * Destroy the hostcache of this handle.
+ */
+void Curl_hostcache_destroy(struct SessionHandle *data);
+
 #endif /* HEADER_CURL_HOSTIP_H */
diff --git a/lib/url.c b/lib/url.c
index 9896dd8c0..75b298706 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -467,11 +467,8 @@ CURLcode Curl_close(struct SessionHandle *data)
     return CURLE_OK;
   }
 
-  if(data->dns.hostcachetype == HCACHE_PRIVATE) {
-    Curl_hash_destroy(data->dns.hostcache);
-    data->dns.hostcachetype = HCACHE_NONE;
-    data->dns.hostcache = NULL;
-  }
+  if(data->dns.hostcachetype == HCACHE_PRIVATE)
+    Curl_hostcache_destroy(data);
 
   if(data->state.rangestringalloc)
     free(data->state.range);
@@ -2131,7 +2128,7 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
       if(data->share->hostcache) {
         /* use shared host cache, first free the private one if any */
         if(data->dns.hostcachetype == HCACHE_PRIVATE)
-          Curl_hash_destroy(data->dns.hostcache);
+          Curl_hostcache_destroy(data);
 
         data->dns.hostcache = data->share->hostcache;
         data->dns.hostcachetype = HCACHE_SHARED;
@@ -2626,12 +2623,6 @@ CURLcode Curl_disconnect(struct connectdata *conn, bool dead_connection)
     conn->dns_entry = NULL;
   }
 
-#if defined(DEBUGBUILD) && defined(AGGRESIVE_TEST)
-  /* scan for DNS cache entries still marked as in use */
-  Curl_hash_apply(data->hostcache,
-                  NULL, Curl_scan_cache_used);
-#endif
-
   Curl_hostcache_prune(data); /* kill old DNS cache entries */
 
   {