As part of the discussion of adding additional thread safety guarantees to MIT Kerberos's GSS-API implementation to support OpenLDAP's use case, Sam Hartman had the following additional questions about how OpenLDAP uses SASL in such a way as to run into this problem. I'm happy to forward answers back to him. I don't understand the usage well enough to explain it myself.
| From: Sam Hartman hartmans@mit.edu | Subject: GSSAPI contexts used in multiple threads | Date: Mon, 03 Mar 2008 16:28:13 -0500 | | Hi. I'm catching up on email. I read a discussion (although I cannot | find it now) of adding support so that an established gss-api context | can be used in multiple threads at the same time. This seems like a | fine feature to add to MIT Kerberos. | | However I'm quite puzzled as to how this works for LDAP or any other | SASL application. SASL is a stream protocol; it presents an ordered | stream across the network connection. In order to guarantee this the | sasl security layer requires that tokens be wrapped and unwrapped in | the same order. If you don't do that you can get into a situation | where the wrap order is different from the unwrap order and you get | spurious gap tokens or out of order tokens. You cannot tell the | difference between this and an attack. Also, since SASL applications | may chunk data into GSS-API tokens in arbitrary order, GSS-API tokens | may not line up with LDAP PDU boundaries. | | So, I'm very confused about how an LDAP implementation could be a | correct application and run into problems with MIT's current thread | safety requirements. | | I'd appreciate it if people who do remember the original discussion | could forward my message to the right place to get an answer. | | Thanks, | | --Sam