chore: add s2n_libcrypto_is_openssl helper, docs, fix test

crypto/s2n_fips.c

@@ -26,17 +26,24 @@
 
 static bool s2n_fips_mode_enabled = false;
 
-/* FIPS mode can be checked if OpenSSL was configured and built for FIPS which then defines OPENSSL_FIPS.
+/* FIPS mode can be checked if OpenSSL was configured and built for FIPS which
+ * then defines OPENSSL_FIPS.
  *
- * AWS-LC always defines FIPS_mode() that you can call and check what the library was built with. It does not define
- * a public OPENSSL_FIPS/AWSLC_FIPS macro that we can (or need to) check here
+ * AWS-LC always defines FIPS_mode() that you can call and check what the
+ * library was built with. It does not define a public OPENSSL_FIPS/AWSLC_FIPS
+ * macro that we can (or need to) check here
  *
- * Safeguard with macro's, for example because Libressl dosn't define
+ * Safeguard with macro's, for example because Libressl doesn't define
  * FIPS_mode() by default.
  *
- * Note: FIPS_mode() does not change the FIPS state of libcrypto. This only returns the current state. Applications
- * using s2n must call FIPS_mode_set(1) prior to s2n_init.
- * */
+ * Note: FIPS_mode() does not change the FIPS state of libcrypto. This only
+ * returns the current state. Applications using s2n must call FIPS_mode_set(1)
+ * prior to s2n_init.
+ *
+ * Note: Developers should use `s2n_is_in_fips_mode()` instead of calling this
+ * directly. `s2n_is_in_fips_mode()` returns libcrypto FIPS status at library
+ * initialization, ie. s2n_init().
+ */
 bool s2n_libcrypto_is_fips(void)
 {
 #if defined(OPENSSL_FIPS) || defined(OPENSSL_IS_AWSLC)

crypto/s2n_fips.h

@@ -23,7 +23,6 @@
 
 int s2n_fips_init(void);
 bool s2n_is_in_fips_mode(void);
-bool s2n_libcrypto_is_fips(void);
 
 struct s2n_cipher_suite;
 S2N_RESULT s2n_fips_validate_cipher_suite(const struct s2n_cipher_suite *cipher_suite, bool *valid);

crypto/s2n_libcrypto.c

@@ -99,16 +99,33 @@ static S2N_RESULT s2n_libcrypto_validate_expected_version_number(void)
 }
 
 /* s2n_libcrypto_is_*() encodes the libcrypto version used at build-time.
- * Currently only captures AWS-LC and BoringSSL. When a libcrypto-dependent
- * branch is required, we prefer these functions where possible to reduce
- # #ifs and avoid potential bugs where the header containing the #define is not
- * included.
+ *
+ * When a libcrypto-dependent branch is required, we prefer these functions
+ * where possible to reduce #ifs and avoid potential bugs where the header
+ * containing the #define is not included.
  */
 
 #if defined(OPENSSL_IS_AWSLC) && defined(OPENSSL_IS_BORINGSSL)
     #error "Both OPENSSL_IS_AWSLC and OPENSSL_IS_BORINGSSL are defined at the same time!"
 #endif
 
+/* Attempt to detect if the libcrypto is OpenSSL.
+ *
+ * Since, quite a few libcrypto (BoringSSL, AWSLC) implementations are ABI
+ * compatible forks of OpenSSL, detecting OpenSSL is done by checking the
+ * absence of other libcrypto variants.
+ *
+ * Note: This check needs to be updated if s2n-tls adds support for a new
+ * libcrypto in the future.
+ */
+bool s2n_libcrypto_is_openssl()
+{
+    bool is_other_libcrypto_variant =
+            s2n_libcrypto_is_boringssl() || s2n_libcrypto_is_libressl() || s2n_libcrypto_is_awslc();
+
+    return !is_other_libcrypto_variant;
+}
+
 bool s2n_libcrypto_is_awslc()
 {
 #if defined(OPENSSL_IS_AWSLC)

crypto/s2n_openssl.h

@@ -56,6 +56,7 @@
     #define S2N_LIBCRYPTO_SUPPORTS_CUSTOM_RAND 0
 #endif
 
+bool s2n_libcrypto_is_openssl();
 bool s2n_libcrypto_is_awslc();
 bool s2n_libcrypto_is_boringssl();
 bool s2n_libcrypto_is_libressl();

tests/unit/s2n_openssl_test.c

@@ -21,21 +21,32 @@ int main(int argc, char** argv)
 {
     BEGIN_TEST();
 
-    const char* env_libcrypto = getenv("S2N_LIBCRYPTO");
-    if (env_libcrypto == NULL) {
-        END_TEST();
-    }
+    {
+        const char* env_libcrypto = getenv("S2N_LIBCRYPTO");
+        if (env_libcrypto == NULL) {
+            END_TEST();
+        }
 
-    if (strcmp(env_libcrypto, "boringssl") == 0) {
-        EXPECT_FALSE(s2n_libcrypto_is_awslc());
-        EXPECT_TRUE(s2n_libcrypto_is_boringssl());
-    } else if (strstr(env_libcrypto, "awslc") != NULL) {
-        EXPECT_TRUE(s2n_libcrypto_is_awslc());
-        EXPECT_FALSE(s2n_libcrypto_is_boringssl());
-    } else {
-        EXPECT_FALSE(s2n_libcrypto_is_awslc());
-        EXPECT_FALSE(s2n_libcrypto_is_boringssl());
-    }
+        if (strcmp(env_libcrypto, "boringssl") == 0) {
+            EXPECT_FALSE(s2n_libcrypto_is_awslc());
+            EXPECT_TRUE(s2n_libcrypto_is_boringssl());
+        } else if (strstr(env_libcrypto, "awslc") != NULL) {
+            EXPECT_TRUE(s2n_libcrypto_is_awslc());
+            EXPECT_FALSE(s2n_libcrypto_is_boringssl());
+        } else {
+            EXPECT_FALSE(s2n_libcrypto_is_awslc());
+            EXPECT_FALSE(s2n_libcrypto_is_boringssl());
+        }
+    };
+
+    /* Check if libcrypto is OpenSSL. */
+    {
+        if (s2n_libcrypto_is_openssl()) {
+            EXPECT_FALSE(s2n_libcrypto_is_awslc());
+            EXPECT_FALSE(s2n_libcrypto_is_boringssl());
+            EXPECT_FALSE(s2n_libcrypto_is_libressl());
+        }
+    };
 
     END_TEST();
 }

tests/unit/s2n_pq_kem_test.c

@@ -41,7 +41,7 @@ int main()
 
 #if defined(OPENSSL_IS_AWSLC) && defined(AWSLC_API_VERSION)
     /* If using non-FIPS AWS-LC >= v1.6 (API vers. 21), expect Kyber512 KEM from AWS-LC */
-    if (!s2n_libcrypto_is_fips() && AWSLC_API_VERSION >= 21) {
+    if (!s2n_is_in_fips_mode() && AWSLC_API_VERSION >= 21) {
         EXPECT_TRUE(s2n_libcrypto_supports_evp_kem());
     }
 #endif

utils/s2n_random.c

@@ -48,6 +48,9 @@
 #include <errno.h>
 #include <limits.h>
 #include <openssl/engine.h>
+/* LibreSSL requires <openssl/rand.h> include.
+ * https://github.com/aws/s2n-tls/issues/153#issuecomment-129651643
+ */
 #include <openssl/rand.h>
 #include <pthread.h>
 #include <stdint.h>