On Tue, Jul 15, 2014, Iaki Baz Castillo wrote:
> Hi, I'm a bit confused about how to free a BIO pair associated to a SSL.
>
> The doc at https://www.openssl.org/docs/crypto/BIO_s_bio.html clearly says:
>
> ----------------------------
> Both halves of a BIO pair should be freed. That is even if one half is
> implicit freed due to a BIO_free_all() or SSL_free() call the other
> half needs to be freed.
>
> EXAMPLE
>
> BIO *internal_bio, *network_bio;
> BIO_new_bio_pair(internal_bio, 0, network_bio, 0);
> SSL_set_bio(ssl, internal_bio, internal_bio);
> ...
> SSL_free(ssl); /* implicitly frees internal_bio */
> BIO_free(network_bio);
> ----------------------------
>
>
> Is it true that I must call to BIO_free(network_bio)? The SSL_free()
> code "seems" to do it by itself!:
>
> --------------------------
> void SSL_free(SSL *s)
> {
> ...
> if (s->rbio != NULL)
> BIO_free_all(s->rbio);
> if ((s->wbio != NULL) && (s->wbio != s->rbio))
> BIO_free_all(s->wbio);
> --------------------------
>
In that example SSL_free is calling BIO_free_all() on "internal_bio" which was
passed using SSL_set_bio().
> In my code I get an obvious crash if I call BIO_free(internal_bio)
> after SSL_free(ssl), but I do NOT get a crash if I call
> BIO_free(network_bio).
>
>
> Anyhow in my code I do not use BIO_new_bio_pair() but instead:
>
> ------------------------
> BIO* internal_bio = BIO_new(BIO_s_mem());
> BIO* network_bio = BIO_new(BIO_s_mem());
> SSL_set_bio(ssl, internal_bio, network_bio);
Your code uses a doesn't use BIO pairs but the same rule applies. The call to
SSL_free() will call BIO_free_all on the BIO or BIOs passed to SSL_set_bio()
internal_bio and network_bio in this example.
>
> void destroy() {
> if (ssl) {
> SSL_free(ssl);
> }
>
>
> // This does NOT crash but, should I do it or not? leak otherwise?
> if (write_bio) {
> BIO_free(write_bio);
> }
> }
There is no indication of what "write_bio" is here.
If write_bio is part of a chain involving the BIOs passed to SSL_set_bio() it
will be free up as part of the SSL_free call. If not you need to explicitly
free it yourself.
Steve.
--
Dr Stephen N. Henson. OpenSSL project core developer.
Commercial tech support now available see: http://www.openssl.org
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