Fix unsalted password comparisons

Unsalted password comparison was broken by the switch from using the ldif base64 function to using the NSPR base64 function.  The old function used to return the number of bytes.  The new one does not.  The code was assuming there was
always a salt, but this is not the case.  Now, the code determines if there
is a salt by comparing the calculated length (hash_len) with the actual number
of bytes in the hash (shaLen).
Reviewed by: nhosoi (Thanks!)

ldap/servers/plugins/pwdstorage/sha_pwd.c

@@ -123,7 +123,16 @@ sha_pw_cmp (const char *userpwd, const char *dbpwd, unsigned int shaLen )
         goto loser;
     } else if ( hash_len >= shaLen ) {
         salt.bv_val = (void*)(dbhash + shaLen);
-        salt.bv_len = SHA_SALT_LENGTH;
+        /* we don't know if the dbpwd is salted or not except for the hash_len
+           if dbpwd is not hashed, hash_len may be 1 or 2 greater than shaLen,
+           depending on the padding, but the difference will always be less than
+           SHA_SALT_LENGTH - so if hash_len - shaLen is less than SHA_SALT_LENGTH,
+           the password is not salted, and dbhash will contain exactly shaLen bytes -
+           if the password is salted, hash_len - shaLen >= SHA_SALT_LENGTH, and
+           dbhash will contain exactly shaLen + SHA_SALT_LENGTH bytes */
+        salt.bv_len = ((hash_len - shaLen) < SHA_SALT_LENGTH) ?
+            0 /* not salted */
+            : SHA_SALT_LENGTH; /* salted */
     } else if ( hash_len >= DS40B1_SALTED_SHA_LENGTH ) {
         salt.bv_val = (void*)dbhash;
         salt.bv_len = OLD_SALT_LENGTH;