Workaround issue in LibreSSL crashing when enumerating digests/ciphers

OpenBSD/LibreSSL reimplemented EVP_get_cipherbyname/EVP_get_digestbyname
and broke calling EVP_get_cipherbynid/EVP_get_digestbyname with an
invalid nid in the process so that it would segfault.

Workaround but doing that NULL check in OpenVPN instead of leaving it
to the library.

Github: see also libressl/openbsd#150

Change-Id: Ia08a9697d0ff41721fb0acf17ccb4cfa23cb3934
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20240508220540.12554-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg28649.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit b3a271b)

src/openvpn/crypto_openssl.c

@@ -386,7 +386,19 @@ show_available_ciphers(void)
 #else
     for (int nid = 0; nid < 10000; ++nid)
     {
+#if defined(LIBRESSL_VERSION_NUMBER)
+        /* OpenBSD/LibreSSL reimplemented EVP_get_cipherbyname and broke
+         * calling EVP_get_cipherbynid with an invalid nid in the process
+         * so that it would segfault. */
+        const EVP_CIPHER *cipher = NULL;
+        const char *name = OBJ_nid2sn(nid);
+        if (name)
+        {
+            cipher = EVP_get_cipherbyname(name);
+        }
+#else  /* if defined(LIBRESSL_VERSION_NUMBER) */
         const EVP_CIPHER *cipher = EVP_get_cipherbynid(nid);
+#endif
         /* We cast the const away so we can keep the function prototype
          * compatible with EVP_CIPHER_do_all_provided */
         collect_ciphers((EVP_CIPHER *) cipher, &cipher_list);
@@ -440,15 +452,27 @@ show_available_digests(void)
 #else
     for (int nid = 0; nid < 10000; ++nid)
     {
+        /* OpenBSD/LibreSSL reimplemented EVP_get_digestbyname and broke
+         * calling EVP_get_digestbynid with an invalid nid in the process
+         * so that it would segfault. */
+#ifdef LIBRESSL_VERSION_NUMBER
+        const EVP_MD *digest = NULL;
+        const char *name = OBJ_nid2sn(nid);
+        if (name)
+        {
+            digest = EVP_get_digestbyname(name);
+        }
+#else  /* ifdef LIBRESSL_VERSION_NUMBER */
         const EVP_MD *digest = EVP_get_digestbynid(nid);
+#endif
         if (digest)
         {
             /* We cast the const away so we can keep the function prototype
              * compatible with EVP_MD_do_all_provided */
             print_digest((EVP_MD *)digest, NULL);
         }
     }
-#endif
+#endif /* if OPENSSL_VERSION_NUMBER >= 0x30000000L */
     printf("\n");
 }