Curl will clear the ex data of the X509_STORE in the ossl_connect_step2 with OpenSSL3.0

[guoxinvmware]

I did this

Steps:

1. I used curl 8.2.1 to connect to a website with OpenSSL 3.0.
2. I called the OpenSSL function X509_STORE_set_ex_data to set the external data with an X509_STORE.
3. Then, I called the OpenSSL function SSL_CTX_set_verify with a callback function.
4. In the callback function, I called the X509_STORE_get_ex_data to get the external data.

Expected:
4. To obtain the external data.

Actual:
4. the external data is NULL. Curl cleared it before the callback function.

Note:
This issue doesn't occur if I use curl with OpenSSL1.0.2.

My investigation:
Root cause:
In lib/vtls/openssl.c, line 280, the macro HAVE_SSL_X509_STORE_SHARE is only defined in curl when OpenSSL >= 1.1.0.
There is a function named Curl_ssl_setup_x509_store at line 3368, and it will be called in the ossl_connect_step2.
For OpenSSL3.0, it will call the OpenSSL function SSL_CTX_set_cert_store, if there is a cached_store and the cache_criteria_met is true.
The SSL_CTX_set_cert_store will clear the external data we set in the ssl_ctx before.

I expected the following

I expected that curl will not clear the ex data in the ossl_connect_step2 with OpenSSL3.0.

curl/libcurl version

curl 8.2.1

operating system

macOS 13.5.1 (22G90)

[icing]

I assume you use CURLOPT_SSL_CTX_FUNCTION to have a callback that installs your ex data at the store.

In curl v7.88.0 we chose to delay store initialization to a later point in time to have a fast handshake. This means that the store you see in your CURLOPT_SSL_CTX_FUNCTION is not the store that is later in effect. And your verify lookup no longer can find the ex data.

I think the best way to fix this is to load the "real" store in case an CURLOPT_SSL_CTX_FUNCTION is registered. The first handshake would take longer, but maybe you can live without that optimization.

@bagder wdyt?

[bagder]

I'm trying to understand @guoxinvmware's use case. I don't think we (can) promise that you can pass data with OpenSSL's API like this.

I think the best way to fix this is to load the "real" store in case an CURLOPT_SSL_CTX_FUNCTION is registered

Agreed.

[guoxinvmware]

Yes, you are right. I use it to install my ex data at the store.

I assume you use CURLOPT_SSL_CTX_FUNCTION to have a callback that installs your ex data at the store.

[icing]

Just add a PR to make the x509 store fully initialised before an application callback is invoked.

Would be nice if you could verify that this fix works for you.

[guoxinvmware]

Verified with https://github.com/curl/curl/pull/11805/commits. This issue is fixed.
Thanks for your efforts!