Segfault when SSL_CTX_get_cert_store returns NULL

[dqp10515]

There appears to be a bug in Mongoose’s OpenSSL TLS integration.

• My goal is: Use mongoose's TLS functionality with openssl.
• My actions were:
  Examined the add_ca_certs() function and its usage of SSL_CTX_get_cert_store()
  and reviewed OpenSSL source code.
• My expectation was: Mongoose handles the case where SSL_CTX_get_cert_store() returns NULL.
• The result I saw:
  Code Analysis Issue:

  static bool add_ca_certs(SSL_CTX *ctx, STACK_OF(X509_INFO) * certs) {
    int i;
    X509_STORE *cert_store = SSL_CTX_get_cert_store(ctx);  // No NULL check
    for (i = 0; i < sk_X509_INFO_num(certs); i++) {
      X509_INFO *cert_info = sk_X509_INFO_value(certs, i);
      if (cert_info->x509 && !X509_STORE_add_cert(cert_store, cert_info->x509))  // Potential NULL pointer dereference
        return false;
    }
    return true;
  }
  

  Crash Scenario:
  SSL_CTX_get_cert_store() can return NULL if the SSL_CTX’s certificate store was not successfully created during context initialization—for example, when X509_STORE_new() fails due to memory allocation failure or other internal initialization errors, leading to a segmentation fault.

  AddressSanitizer:DEADLYSIGNAL
  =================================================================
  ==296176==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000090 (pc 0x7f55c6506df4 bp 0x602000002190 sp 0x7ffddd145338 T0)
  ==296176==The signal is caused by a READ memory access.
  ==296176==Hint: address points to the zero page.
      #0 0x7f55c6506df4 in X509_STORE_lock (openssl/libcrypto.so.1.1+0x209df4)
      #1 0x7f55c6507baf in X509_STORE_add_cert (openssl/libcrypto.so.1.1+0x20abaf)
      #2 0x5a1b00 in add_ca_certs mongoose/tutorials/mqtt/mqtt-client/src/tls_openssl.c:45:29
      #3 0x5a002e in mg_tls_init mongoose/tutorials/mqtt/mqtt-client/src/tls_openssl.c:178:10
      #4 0x4cbb67 in mqtt_ev_handler mongoose/tutorials/mqtt/mqtt-client/main.c:49:7
      #5 0x4dc0c2 in mg_call mongoose/tutorials/mqtt/mqtt-client/src/event.c:22:22
      #6 0x59b7b4 in connect_conn mongoose/tutorials/mqtt/mqtt-client/src/sock.c:368:5
      #7 0x53dda5 in mg_mgr_poll mongoose/tutorials/mqtt/mqtt-client/src/sock.c:752:45
      #8 0x4caf73 in main mongoose/tutorials/mqtt/mqtt-client/main.c:117:5
      #9 0x7f55c5eea0b2 in __libc_start_main /build/glibc-eX1tMB/glibc-2.31/csu/../csu/libc-start.c:308:16
      #10 0x41d6bd in _start (mongoose/tutorials/mqtt/mqtt-client/client+0x41d6bd)
  
  AddressSanitizer can not provide additional info.
  SUMMARY: AddressSanitizer: SEGV (openssl/libcrypto.so.1.1+0x209df4) in X509_STORE_lock
  ==296176==ABORTING
  

Environment

• mongoose version: 235dafe
• Compiler/IDE and SDK: gcc
• Target RTOS/OS (if applicable): Ubuntu 20.04

[scaprile]

Please don't paste our code, we know it, just link to it in the repo if necessary.
And why would that be NULL ? What are you doing ? We test with a CI/CD pipeline and we don't get segfaults.
Please correctly describe your OpenSSL version and exactly what you do. If you don't use Mongoose the way it is intended to be used, our code is embedded oriented and has minimal checks, one of our goals is not to bloat the user flash in a microcontroller, so our code does not teach you how to use it, we have docs for that.
We'll reopen this if necessary, closing for now

[dqp10515]

To clarify the context: we're conducting robustness testing on how Mongoose handles OpenSSL API behaviors under resource-constrained scenarios, which aligns with Mongoose's embedded system focus. Using fault injection to simulate memory allocation failures in OpenSSL internals, we systematically tested various edge cases. We found that Mongoose demonstrates excellent robustness overall—this is actually the only issue we discovered across extensive testing. The test case is straightforward: running the MQTT client-server example (mongoose/tutorials/mqtt/mqtt-client/client -u mqtts://localhost:8883 -v 3 and mongoose/tutorials/mqtt/mqtt-server/example 1883) with fault injection forcing X509_STORE_new() to fail during SSL_CTX initialization. While SSL_CTX_get_cert_store() returning NULL is rare in normal operation, it's documented OpenSSL behavior when internal allocation fails, and such scenarios are more realistic in the resource-constrained embedded environments that Mongoose targets. A simple NULL check would prevent undefined behavior with minimal code overhead, but I understand and respect Mongoose's minimal-footprint philosophy and leave it to your judgment whether this edge case aligns with your design goals.

[dqp10515]

The version of OpenSSL is 1.1.

[scaprile]

That is a completely different story.
Yet, no microcontrolled system uses OpenSSL. I'll see if we can handle this scenario with a minimal check.
Thank you.

[dqp10515]

Thank you for your response.