OpenSSL 3, "reuse" capability in `d2i_TYPE_BIO` and documentation

[Thomas Bailleux]

Hi Tomas,

Thanks for your reply.

I wonder if we shouldn't be providing a new API for X509 instead. We
already have `PEM_read_bio_PrivateKey_ex` and `d2i_PrivateKey_ex_bio`, what
about having `PEM_read_bio_X509_ex` and `d2i_X509_ex_bio` too?
I feel like the documentation can be confusing with all these conditions
(OK if using OSSL_LIB_CTX, otherwise not OK, and in both cases *x is freed
even on error etc).

Also, we can move this discussion to the PR you just opened if you prefer.

Regards,

- thomas

On Tue, Oct 3, 2023 at 3:47 PM Tomas Mraz <tomas at openssl.org> wrote:

> Hello Thomas,
>
> I've created a pull request that should clarify the matter:
>
> https://github.com/openssl/openssl/pull/22265
>
> Please look there.
>
> Tomas Mraz, OpenSSL
>
> On Mon, 2023-10-02 at 09:41 +0200, Thomas Bailleux wrote:
> > Hello OpenSSL,
> >
> > I'm currently migrating a codebase from OpenSSL 1.1.1 to OpenSSL 3.
> > Since I may use OpenSSL providers in the future, I decided to use
> > these new `_ex` functions from OpenSSL 3.
> >
> > While reading the "Old functions that should be changed" from the
> > migration guide[1], I came across an oddity: it is claimed that in
> > order to use a non-default library context when parsing an `X509` or
> > an `EVP_PKEY`, `TYPE_new_ex` must be used (e.g. `X509_new_ex`), and
> > then we have to use the "reuse" capability from the various parsing
> > functions (`PEM_read_bio_X509`):
> >
> > > Some functions can be passed an object that has already been set up
> > > with a library context such as d2i_X509(3), d2i_X509_CRL(3),
> > > d2i_X509_REQ(3) and d2i_X509_PUBKEY(3). If NULL is passed instead
> > > then the created object will be set up with the default library
> > > context. Use X509_new_ex(3), X509_CRL_new_ex(3), X509_REQ_new_ex(3)
> > > and X509_PUBKEY_new_ex(3) if a library context is required.
> >
> > So basically we have to do the following:
> >
> > > BIO *bio;
> > > OSSL_LIB_CTX* lib_ctx;
> > > X509 *x509 = X509_new_ex(lib_ctx, NULL);
> > > if (d2i_X509_bio(bio, &x509) != NULL) {
> > >   // success
> > > } else {
> > >   // error
> > > }
> > >
> >
> >
> > However, in the `D2I_X509` manpage[2], the following is stated:
> >
> > > On a successful return, if *a is not NULL then it is assumed that
> > > *a contains a valid TYPE structure and an attempt is made to reuse
> > > it. This "reuse" capability is present for historical compatibility
> > > but its use is strongly discouraged (see BUGS below, and the
> > > discussion in the RETURN VALUES section).
> > > …
> > > BUGS
> > > …
> > > As a result of the above issues the "reuse" behaviour is strongly
> > > discouraged.
> > >
> >
> > So if I'm understanding correctly, this "reuse" capability is
> > discouraged, still present for historical compatibility, but in
> > OpenSSL 3 we have to use it if we want to use a custom library
> > context.
> >
> > This divergence between these two bits of documentation bothers me.
> > Do you have an opinion on this?
> >
> > Regards,
> >
> > - thomas
> >
> >
> > [1]:
> >
> https://www.openssl.org/docs/man3.1/man7/migration_guide.html#Using-a-Library-Context---Old-functions-that-should-be-changed
> > [2]: https://www.openssl.org/docs/man3.1/man3/d2i_X509.html
>
> --
> Tomáš Mráz, OpenSSL
>
>
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