Allow multiple entries without a Subject even if unique_subject == yes

It is quite likely for there to be multiple certificates with empty
subjects, which are still distinct because of subjectAltName. Therefore
we allow multiple certificates with an empty Subject even if
unique_subject is set to yes.
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5444)

apps/ca.c

@@ -1721,6 +1721,20 @@ static int do_body(X509 **xret, EVP_PKEY *pkey, X509 *x509,
         goto end;
     }
 
+    if (row[DB_name][0] == '\0') {
+        /*
+         * An empty subject! We'll use the serial number instead. If
+         * unique_subject is in use then we don't want different entries with
+         * empty subjects matching each other.
+         */
+        OPENSSL_free(row[DB_name]);
+        row[DB_name] = OPENSSL_strdup(row[DB_serial]);
+        if (row[DB_name] == NULL) {
+            BIO_printf(bio_err, "Memory allocation failure\n");
+            goto end;
+        }
+    }
+
     if (db->attributes.unique_subject) {
         OPENSSL_STRING *crow = row;
 
@@ -2034,6 +2048,11 @@ static int do_revoke(X509 *x509, CA_DB *db, REVINFO_TYPE rev_type,
     else
         row[DB_serial] = BN_bn2hex(bn);
     BN_free(bn);
+    if (row[DB_name] != NULL && row[DB_name][0] == '\0') {
+        /* Entries with empty Subjects actually use the serial number instead */
+        OPENSSL_free(row[DB_name]);
+        row[DB_name] = OPENSSL_strdup(row[DB_serial]);
+    }
     if ((row[DB_name] == NULL) || (row[DB_serial] == NULL)) {
         BIO_printf(bio_err, "Memory allocation failure\n");
         goto end;

doc/man1/ca.pod

@@ -469,6 +469,10 @@ versions of OpenSSL.  However, to make CA certificate roll-over easier,
 it's recommended to use the value B<no>, especially if combined with
 the B<-selfsign> command line option.
 
+Note that it is valid in some circumstances for certificates to be created
+without any subject. In the case where there are multiple certificates without
+subjects this does not count as a duplicate. 
+
 =item B<serial>
 
 A text file containing the next serial number to use in hex. Mandatory.