Detect and prevent recursive config parsing

If a malformed config file is provided such as the following:

openssl_conf = openssl_init
[openssl_init]
providers = provider_sect
[provider_sect]
 = provider_sect

The config parsing library will crash overflowing the stack, as it
recursively parses the same provider_sect ad nauseum.

Prevent this by maintaing a list of visited nodes as we recurse through
referenced sections, and erroring out in the event we visit any given
section node more than once.

Note, adding the test for this revealed that our diagnostic code
inadvertently pops recorded errors off the error stack because
provider_conf_load returns success even in the event that a
configuration parse failed. The call path to provider_conf_load has been
updated in this commit to address that shortcoming, allowing recorded
errors to be visibile to calling applications.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22898)

1 files changed, 8 insertions, 0 deletions

diff --git a/test/recursive.cnf b/test/recursive.cnf
new file mode 100644
index 0000000..505733a
--- /dev/null
+++ b/test/recursive.cnf
@@ -0,0 +1,8 @@
+openssl_conf = openssl_init
+config_diagnostics = yes
+
+[openssl_init]
+providers = provider_sect
+
+[provider_sect]
+ = provider_sect