CVE-2009-3623: Null Pointer Dereference

Quoting from upstream patch: On setting up the callback to the client, we attempt to use the same authentication flavor the client did. We find an rpc cred to use by calling rpcauthlookupcredcache(), which assumes that the given authentication flavor has a credentials cache. However, this is not required to be true--in particular, authnull does not use one. Instead, we should call the auth's lookupcred() method.

Without this, a client attempting to mount using nfsv4 and authnull triggers a null dereference.

The code was introduced in upstream commit 3cef9ab2 (v2.6.31-rc1), fixed in 886e3b7f (v2.6.32-rc1), and was later replaced by 80fc015b.