OpenSSL: Fix --crl-verify not loading multiple CRLs in one file

Lack of this led people accepting multiple CAs to use capath,
which already supports multiple CRLs. But capath mode itself
is somewhat ugly: you have to create new file/symlink every time
CRL is updated, and there's no good way to clean them up without
restarting OpenVPN, since any gap in the sequence would cause it
to lose sync (see trac 623).

mbedtls crypto backend already loads multiple CRLs as is, so
it doesn't need this fix.

The patch also includes some logging changes which I think are useful.

Trac: #623

Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20200407174436.238933-1-wgh@torlan.ru>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg19710.html

Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 05229fb)

src/openvpn/ssl_openssl.c

@@ -1023,7 +1023,6 @@ void
 backend_tls_ctx_reload_crl(struct tls_root_ctx *ssl_ctx, const char *crl_file,
                            const char *crl_inline)
 {
-    X509_CRL *crl = NULL;
     BIO *in = NULL;
 
     X509_STORE *store = SSL_CTX_get_cert_store(ssl_ctx->ctx);
@@ -1064,21 +1063,39 @@ backend_tls_ctx_reload_crl(struct tls_root_ctx *ssl_ctx, const char *crl_file,
         goto end;
     }
 
-    crl = PEM_read_bio_X509_CRL(in, NULL, NULL, NULL);
-    if (crl == NULL)
+    int num_crls_loaded = 0;
+    while (true)
     {
-        msg(M_WARN, "CRL: cannot read CRL from file %s", crl_file);
-        goto end;
-    }
+        X509_CRL *crl = PEM_read_bio_X509_CRL(in, NULL, NULL, NULL);
+        if (crl == NULL)
+        {
+            /*
+             * PEM_R_NO_START_LINE can be considered equivalent to EOF.
+             */
+            bool eof = ERR_GET_REASON(ERR_peek_error()) == PEM_R_NO_START_LINE;
+            /* but warn if no CRLs have been loaded */
+            if (num_crls_loaded > 0 && eof)
+            {
+                /* remove that error from error stack */
+                (void)ERR_get_error();
+                break;
+            }
 
-    if (!X509_STORE_add_crl(store, crl))
-    {
-        msg(M_WARN, "CRL: cannot add %s to store", crl_file);
-        goto end;
-    }
+            crypto_msg(M_WARN, "CRL: cannot read CRL from file %s", crl_file);
+            break;
+        }
 
+        if (!X509_STORE_add_crl(store, crl))
+        {
+            X509_CRL_free(crl);
+            crypto_msg(M_WARN, "CRL: cannot add %s to store", crl_file);
+            break;
+        }
+        X509_CRL_free(crl);
+        num_crls_loaded++;
+    }
+    msg(M_INFO, "CRL: loaded %d CRLs from file %s", num_crls_loaded, crl_file);
 end:
-    X509_CRL_free(crl);
     BIO_free(in);
 }