freeradius2: backport fix for CVE-2015-4680

freeradius2: backport fix for CVE-2015-4680

Backport upstream commit 5e698b407dcac2bc45cf03484bac4398109d25c3 to fix
missing intermediate certificate validation in Freeradius2.

Advisory:

The FreeRADIUS server relies on OpenSSL to perform certificate validation,
including Certificate Revocation List (CRL) checks. The FreeRADIUS usage of
OpenSSL, in CRL application, limits the checks to leaf certificates,
therefore not detecting revocation of intermediate CA certificates.

An unexpired client certificate, issued by an intermediate CA with a revoked
certificate, is therefore accepted by FreeRADIUS.

Specifically sets the X509_V_FLAG_CRL_CHECK flag for leaf certificate CRL
checks, but does not use X509_V_FLAG_CRL_CHECK_ALL for CRL checks on the
complete trust chain.

The FreeRADIUS project advises that the recommended configuration is to use
self-signed CAs for all EAP-TLS methods.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>