mod_ssl: fix leak of X509 reference in ssl_hook_Access_classic quick renegotiation path

[rootvector2]

While reading ssl_hook_Access_classic(), I noticed that the renegotiate_quick branch obtains a peer certificate with SSL_get_peer_certificate(ssl) and never releases it on the common path.

The leak

cert_stack = (STACK_OF(X509) *)SSL_get_peer_cert_chain(ssl);
cert = SSL_get_peer_certificate(ssl);   /* refcount +1, owned by caller */

if (!cert_stack || (sk_X509_num(cert_stack) == 0)) {
    ...
    cert_stack = sk_X509_new_null();
    sk_X509_push(cert_stack, cert);     /* (A) ownership now in stack */
}
...
if (cert_stack != SSL_get_peer_cert_chain(ssl)) {
    sk_X509_pop_free(cert_stack, X509_free);  /* frees (A) */
}

SSL_get_peer_certificate() increments the X509 refcount and returns a reference the caller owns. Every other call site in this file releases it with X509_free() (lines 319, 615, 1531).

The trailing sk_X509_pop_free() only runs when we built the stack ourselves — i.e., only when the original SSL_get_peer_cert_chain() was empty/NULL. In the common case where the peer chain already contains certificates, the reference is never freed, leaking one X509 refcount per quick renegotiation. The two early-return paths ("Cannot find certificate storage" and the X509_STORE_CTX_init failure return added in bz 65902) leak unconditionally.

This matches the documented OpenSSL contract for SSL_get_peer_certificate(3):

The reference count of the X509 object [...] is incremented by one [...]. The X509 object must be explicitly freed using X509_free().

The fix

Track the owned reference as peer_cert. When ownership is transferred into the freshly-created stack via sk_X509_push(), clear peer_cert so sk_X509_pop_free() remains the sole owner and there is no double free. Release peer_cert on every exit path.

Only affects TLS ≤ 1.2 renegotiation (ssl_hook_Access_classic); TLS 1.3 has no renegotiation and uses ssl_hook_Access_modern.

Notes for the reviewer

• Found by static reading. I have not run a leak-sanitizer reproducer; the analysis follows the OpenSSL ownership contract and the pattern used by the other SSL_get_peer_certificate() sites in this file.
• No CHANGES entry — happy to add one in the format the committer prefers.