Sorry for the delay. I needed to do some due diligence before responding.
On 06/06/15 13:35, Howard Chu wrote:
Doug Leavitt wrote:
Hi,
OpenSSL now has X509_V_FLAG_PARTIAL_CHAIN support in the code base as
of 1.0.2a.
I would like to submit a patch to enable X509_V_FLAG_PARTIAL_CHAIN
support
in OpenLDAP libldap, assuming it exists in the version of OpenSSL
being use to
build
OpenLDAP.
What's the use case? It appears that the feature has been in OpenSSL
since around 2012, but I don't see much documentation or chatter about
it. Why is it useful, and do GnuTLS and MozNSS already support a
similar feature?
The use case is:
You have a certificate issued by a CA:
rootCA -> mysystem
You don't want to trust all of the certificates issued by that CA. You
only want to trust that particular certificate.
OpenSSL by default ignores trust-list entries that are not for root
CAs. Adding just the "mysystem" certificate has no effect. With this
change, you can add the "mysystem" certificate and that will cause
OpenSSL to accept this certificate, even though the trust list does not
include the CA's root certificate.
A more complex case:
rootCA -> mycompanyCA -> mysystem
You don't want to trust all of the certificates issued by that CA. You
only want to trust certificates issued by your company's CA. Again,
OpenSSL by default will not let you trust an intermediate CA. With this
change, you can add mycompanyCA's certificate and that will cause
OpenSSL to accept certificates signed by your company CA.
The reason this is coming up now, is that the old Mozilla libldap/NSS
combination supported this by default but the combination of
OpenLDAP/OpenSSL currently does not. We first discovered the issue back
in 2012 and realized that OpenSSL did not support partial chains.
Working through our security team the project that discovered the issue
convinced the OpenSSL upstream to add the X509_V_FLAG_PARTIAL_CHAIN
support so that eventually we could find a way to incorporate that
support back into OpenLDAP.
Additionally we have since uncovered some programs that depend on this
Mozilla functionality and we would like to see it supported in the
OpenLDAP/OpenSSL so those applications can finish moving off Mozilla
libldap/NSS.
Moving forward to today it looks like OpenSSL has the support, disabled
by default, and both GNUTLS and NSS have the support for partial chains
enabled by default.
In GNUTLS, the support is here:
https://gitlab.com/gnutls/gnutls/blob/master/lib/x509/verify.c#L868
In NSS the support is here:
http://mxr.mozilla.org/security/source/security/nss/lib/certhigh/certvfy.c#532
where intermediate certificates are processed (with the final decision
at 557), and that leaf certificates are handled at
http://mxr.mozilla.org/security/source/security/nss/lib/certhigh/certvfy.c#916
In OpenSSL the support is disabled by default here:
https://github.com/openssl/openssl/blob/master/crypto/x509/x509_vfy.c#L819
Our hope is to have OpenLDAP/OpenSSL be either on par with OpenLDAP/NSS and
OpenLDAP/GNUTLS or at least have the option of be on par without having to
maintain a downstream code fork.
The code change itself is simple. At a minimum it is as simple as adding:
#ifdef X509_V_FLAG_PARTIAL_CHAIN
/*
* Allow intermediate or leaf certificates in the trust list to
* act as trust anchors.
*/
X509_STORE_set_flags(SSL_CTX_get_cert_store(ctx),
X509_V_FLAG_PARTIAL_CHAIN);
#endif
after:
http://www.openldap.org/devel/gitweb.cgi?p=openldap.git;a=blob;f=libraries/libldap/tls_o.c;h=5d2367c6c1cc1e45707dbd070dadf88a556f8d74;hb=HEAD#l381
From our investigation always adding the support does not seem to be
harmful in any way and maintains compatibility with some existing software.
Hence the original question.
Thanks in advance for your consideration,
Doug.
Before I submit any patch I would like to know that would be acceptable
for integration.
Should support always be enabled if the version of OpenSSL has it
e.g. ifdef on X509_V_FLAG_PARTIAL_CHAIN
Should it be a config time option check and ifdef enable if found in
e.g. like the ifdef on HAVE_OPENSSL_CRL
Are there more requirements that is required in the patch, before it
would
be accepted such as ldap_set_option support?
Thanks in advance,
Doug.
