Resolves: bug 231507

Bug Description: Modification of directory entries with VLV-indexed null-value attributes results in server crash
Reviewed by: nkinder, nhosoi, prowley (Thanks!)
Fix Description: The value lowest_value is defined outside the loop that loops through all the attributes in the vlv sort specification (e.g. usually something like cn givenname o ou sn if defined by the console browsing index).  lowest_value is not reset for each loop iteration.  So if it goes through the loop one time for e.g. givenname, and givenname has values, lowest_value will point to the lowest value of givenname until the key is created, then it is freed.  So the next loop iteration uses o, and if for example o does not have any values, lowest_value will point to the already freed memory used by the givenname iteration, which is now garbage (e.g. the lowest_value->bv_len may be very large, which is the probably cause of the malloc out of memory errors seen by the customer).  The solution is to reset lowest_value to NULL before each loop iteration (I did this by moving the declaration and initialization of lowest_value inside the loop scope) and testing for lowest_value == NULL before trying to use it.
Platforms tested: RHEL4
Flag Day: no
Doc impact: no

ldap/servers/slapd/back-ldbm/vlv.c

@@ -508,7 +508,7 @@ vlv_getindices(IFP callback_fn,void *param, backend *be)
 static struct vlv_key *
 vlv_create_key(struct vlvIndex* p, struct backentry* e)
 {
-    struct berval val, *lowest_value = NULL;
+    struct berval val;
     unsigned char char_min = 0x00;
     unsigned char char_max = 0xFF;
     struct vlv_key *key= vlv_key_new();
@@ -530,7 +530,7 @@ vlv_create_key(struct vlvIndex* p, struct backentry* e)
 				/* xxxPINAKI */
 				/* need to free some stuff! */
 		        Slapi_Value **cvalue = NULL;
-        		struct berval **value = NULL;
+        		struct berval **value = NULL, *lowest_value = NULL;
                 int free_value= 0;
                 if (attr != NULL && !valueset_isempty(&attr->a_present_values))
 				{
@@ -587,7 +587,7 @@ vlv_create_key(struct vlvIndex* p, struct backentry* e)
                     unsigned int i;
                     char *attributeValue = NULL;
                     /* Bug 605477 : Don't malloc 0 bytes */
-                    if (attr != NULL && lowest_value->bv_len != 0) {
+                    if (attr != NULL && lowest_value && lowest_value->bv_len != 0) {
                          attributeValue = (char*)slapi_ch_malloc(lowest_value->bv_len);
                          for(i=0;i<lowest_value->bv_len;i++)
                        	 {
@@ -615,7 +615,7 @@ vlv_create_key(struct vlvIndex* p, struct backentry* e)
                     /* If the forward-sorted attribute is absent or has no 
                      * value, we need to use the value of 0xFF.
                      */
-                     if (attr != NULL && lowest_value->bv_len > 0) {
+                     if (attr != NULL && lowest_value && lowest_value->bv_len > 0) {
                          vlv_key_addattr(key,lowest_value);
                      } else {
                          val.bv_val = (void*)&char_max;