Ingmar Runge provided a source snippet that caused a crash. The reason for

the crash was that libcurl internally was a bit confused about who owned the
DNS cache at all times so if you created an easy handle that uses a shared
DNS cache and added that to a multi handle it would crash. Now we keep more
careful internal track of exactly what kind of DNS cache each easy handle
uses: None, Private (allocated for and used only by this single handle),
Shared (points to a cache held by a shared object), Global (points to the
global cache) or Multi (points to the cache within the multi handle that is
automatically shared between all easy handles that are added with private
caches).

1 files changed, 10 insertions, 7 deletions

diff --git a/lib/url.c b/lib/url.c
index 85537b2ce..6e50e7a03 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -205,7 +205,7 @@ CURLcode Curl_close(struct SessionHandle *data)
 
   if ( ! (data->share && data->share->hostcache) ) {
     if ( !Curl_global_host_cache_use(data)) {
-      Curl_hash_destroy(data->hostcache);
+      Curl_hash_destroy(data->dns.hostcache);
     }
   }
 
@@ -1392,8 +1392,10 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
       if(data->share) {
         Curl_share_lock(data, CURL_LOCK_DATA_SHARE, CURL_LOCK_ACCESS_SINGLE);
 
-        if(data->share->hostcache == data->hostcache)
-          data->hostcache = NULL;
+        if(data->dns.hostcachetype == HCACHE_SHARED) {
+          data->dns.hostcache = NULL;
+          data->dns.hostcachetype = HCACHE_NONE;
+        }
 
         if(data->share->cookies == data->cookies)
           data->cookies = NULL;
@@ -1413,11 +1415,12 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
         data->share->dirty++;
 
         if(data->share->hostcache) {
-          /* use shared host cache, first free own one if any */
-          if(data->hostcache)
-            Curl_hash_destroy(data->hostcache);
+          /* use shared host cache, first free the private one if any */
+          if(data->dns.hostcachetype == HCACHE_PRIVATE)
+            Curl_hash_destroy(data->dns.hostcache);
 
-          data->hostcache = data->share->hostcache;
+          data->dns.hostcache = data->share->hostcache;
+          data->dns.hostcachetype = HCACHE_SHARED;
         }
 #if !defined(CURL_DISABLE_HTTP) && !defined(CURL_DISABLE_COOKIES)
         if(data->share->cookies) {