Segfault in backend_connect if backend server mech list empty (bug 3166)

[Michael Bacon]

If the backend server in a murder advertises no mechanisms in its  
capability string (say, if it's expecting a STARTTLS before offering  
PLAIN), the proxyd will seg fault.  This is due to an xstrdup call on  
a NULL pointer (as returned from backend.c:ask_capability()).  This  
patch simply checks for the NULL condition and replaces it with an  
empty string.

Bug submitted with patch as 3166.

https://bugzilla.andrew.cmu.edu/show_bug.cgi?id=3166

Michael Bacon
ITS Messaging
UNC Chapel Hill



--- backend.c.1off      Sun Jul  5 23:35:47 2009
+++ backend.c   Mon Jul  6 00:02:55 2009
@@ -457,8 +457,14 @@
      if ((server[0] != '/') ||
         (strcmp(prot->sasl_service, "lmtp") &&
          strcmp(prot->sasl_service, "csync"))) {
-       char *mlist = xstrdup(mechlist); /* backend_auth is  
destructive */

+        char *mlist;
+        if (mechlist != NULL) {
+           mlist = xstrdup(mechlist); /* backend_auth is destructive */
+        } else {
+            mlist = xstrdup("");
+        }
+
         if ((r = backend_authenticate(ret, prot, &mlist, userid,
                                       cb, auth_status))) {
             syslog(LOG_ERR, "couldn't authenticate to backend server:  
%s",