[openssl-users] Certificate Verify and non-root Trust Anchors

[Viktor Dukhovni]

> On Dec 11, 2017, at 7:35 PM, Dr. Pala <madwolf at openca.org> wrote:
> 
>> Perhaps you ended up creating a parameter structure with a
>> depth limit that's too small.  Just configuring partial
>> chains will never yield a chain that is longer than it
>> otherwise would be.  In fact you generally get shorter
>> chains.  So, no this is not a result of using the
>> new flag, but may be a result of how you're going about
>> setting the flag.

> I actually do not set anything but the flag in the verify parameter, that is (error checking removed for clarity):
> param = X509_VERIFY_PARAM_new();
> X509_STORE_CTX_set0_param(ctx, param);
> X509_VERIFY_PARAM_set_flags(param, X509_V_FLAG_PARTIAL_CHAIN);

There's the problem, you're creating new parameters, instead of
modifying the default parameters.

Instead, you must call:

	param = X509_STORE_CTX_get0_param(ctx);
        X509_VERIFY_PARAM_set_flags(param, X509_V_FLAG_PARTIAL_CHAIN);

> With this setting, I get the error..

Not surprising, the parameters you created don't have the default depth
setting.

> which is the strange part as you said (the chain can not be longer :D). Maybe the code thinks that if you have a SubCA then you should have an additional level.. and since you do not have it, it sends the error... ???
>>> ... any suggestion on how to fix this ? Do you think it is actually a bug ? ... or am I missing some other configs / setting I should have done for the verify param ?
>>> 
>> You should obtain a reference to the existing parameters
>> from the context, and modify these to add the new flag.
>> 
>> 
> Well.. considering the code structure, the flags should be ok
> (since I just set it and then use it right away...) ???

Actually, no.  You're losing all the verification parameter initialization
done by X509_STORE_CTX_new():

    ctx->param = X509_VERIFY_PARAM_new();
    if (!ctx->param) {
        X509err(X509_F_X509_STORE_CTX_INIT, ERR_R_MALLOC_FAILURE);
        return 0;
    }

    /*
     * Inherit callbacks and flags from X509_STORE if not set use defaults.
     */
    if (store)
        ret = X509_VERIFY_PARAM_inherit(ctx->param, store->param);
    else
        ctx->param->inh_flags |= X509_VP_FLAG_DEFAULT | X509_VP_FLAG_ONCE;

    if (store) {
        ctx->verify_cb = store->verify_cb;
        /* Seems to always be 0 in OpenSSL, else must be idempotent */
        ctx->cleanup = store->cleanup;
    } else
        ctx->cleanup = 0;

    if (ret)
        ret = X509_VERIFY_PARAM_inherit(ctx->param,
                                        X509_VERIFY_PARAM_lookup("default"));

-- 
	Viktor.