Do I need to call BIO_free(network_bio) or not?

[Iñaki Baz Castillo]

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 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);

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);
}
}
------------------------


Thanks a lot.




--
Iñaki Baz Castillo
<i...@aliax.net>
______________________________________________________________________
OpenSSL Project http://www.openssl.org
User Support Mailing List openss...@openssl.org
Automated List Manager majo...@openssl.org

[Iñaki Baz Castillo]

some new comments:

First of all the example in the doc is wrong:

--------------

BIO *internal_bio, *network_bio;
BIO_new_bio_pair(internal_bio, 0, network_bio, 0);

--------------

It should be:

--------------
BIO *internal_bio, *network_bio;
BIO_new_bio_pair(&internal_bio, 0, &network_bio, 0);
--------------


Second: I'm now using BIO_new_bio_pair() by following the steps of the
doc. If I call to BIO_free(network_bio) after SSL_free(ssl) (as the
documentation clearly states) then I get a funny crash. So it seems
that SSL_free does, in fact, free both BIOs, am I right?

[Iñaki Baz Castillo]

May somebody please answer this question? The documentation is
confusing and contradictory, and the issue is important (memory leak
or crash if the bad choice is made).

Thanks.

[Dr. Stephen Henson]

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

[Iñaki Baz Castillo]

2014-07-17 14:29 GMT+02:00 Dr. Stephen Henson <st...@openssl.org>:
> 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.

Thanks. Then the example in the documentation is really wrong and may
cause a crash, right? I mean the "BIO_free(network_bio);" line at the
end.

--
Iñaki Baz Castillo
<i...@aliax.net>

[Thulasi Goriparthi]

In the example, only internal_bio is set using SSL_set_bio as below.

SSL_set_bio(ssl, internal_bio, internal_bio);

network_bio is not linked to SSL session. So it has to be freed explicitly.