Markus Koetter filed debian bug report #355715 which identified a problem

with the multi interface and multi-part formposts. The fix from February
22nd could make the Curl_done() function get called twice on the same
connection and it was not designed for that and thus tried to call free() on
an already freed memory area!

CHANGES

@@ -7,6 +7,12 @@
                                   Changelog
 
 Daniel (7 March 2006)
+- Markus Koetter filed debian bug report #355715 which identified a problem
+  with the multi interface and multi-part formposts. The fix from February
+  22nd could make the Curl_done() function get called twice on the same
+  connection and it was not designed for that and thus tried to call free() on
+  an already freed memory area!
+
 - Peter Heuchert made sure the CURLFTPSSL_CONTROL setting for CURLOPT_FTP_SSL
   is used properly.
 

RELEASE-NOTES

@@ -15,6 +15,7 @@ This release includes the following changes:
 
 This release includes the following bugfixes:
 
+ o multi-part formpost with multi interface crash
  o the CURLFTPSSL_CONTROL setting for CURLOPT_FTP_SSL is acknowledged
  o "SSL: couldn't set callback" is now a less serious problem
  o Interix build fix
@@ -28,6 +29,7 @@ Other curl-related news since the previous public release:
 This release would not have looked like this without help, code, reports and
 advice from friends like these:
 
- Gisle Vanem, Dan Fandrich, Thomas Klausner, Todd Vierling, Peter Heuchert
+ Gisle Vanem, Dan Fandrich, Thomas Klausner, Todd Vierling, Peter Heuchert,
+ Markus Koetter
 
         Thanks! (and sorry if I forgot to mention someone)

lib/url.c

@@ -3982,6 +3982,11 @@ CURLcode Curl_done(struct connectdata **connp,
   struct connectdata *conn = *connp;
   struct SessionHandle *data=conn->data;
 
+  if(conn->bits.done)
+    return CURLE_OK; /* Curl_done() has already been called */
+
+  conn->bits.done = TRUE; /* called just now! */
+
   /* cleanups done even if the connection is re-used */
   if(conn->bits.rangestringalloc) {
     free(conn->range);
@@ -4047,6 +4052,7 @@ CURLcode Curl_do(struct connectdata **connp, bool *done)
   struct connectdata *conn = *connp;
   struct SessionHandle *data=conn->data;
 
+  conn->bits.done = FALSE; /* Curl_done() is not called yet */
   conn->bits.do_more = FALSE; /* by default there's no curl_do_more() to use */
 
   if(conn->curl_do) {

lib/urldata.h

@@ -432,6 +432,10 @@ struct ConnectBits {
   bool trailerHdrPresent; /* Set when Trailer: header found in HTTP response.
                              Required to determine whether to look for trailers
                              in case of Transfer-Encoding: chunking */
+  bool done;          /* set to FALSE when Curl_do() is called and set to TRUE
+                         when Curl_done() is called, to prevent Curl_done() to
+                         get invoked twice when the multi interface is
+                         used. */
 };
 
 struct hostname {