[Qemu-devel] [PATCH v4 09/10] chardev: add support for ACLs for TLS clients

["Daniel P. Berrange" <berrange@redhat.com>]

Currently any client which can complete the TLS handshake
is able to use a chardev server. The server admin can turn
on the 'verify-peer' option for the x509 creds to require
the client to provide a x509 certificate. This means the
client will have to acquire a certificate from the CA before
they are permitted to use the chardev server. This is still
a fairly weak bar.

This adds a 'tls-acl=ACL-ID' option to the socket chardev
backend which takes the ID of a previously added 'QAuthZ'
object instance. This ACL will be used to validate the client's
x509 distinguished name. Clients failing the ACL will not be
permitted to use the chardev server.

For example to setup an ACL that only allows connection from
a client whose x509 certificate distinguished name contains
'CN=fred', you would use:

  $QEMU -object tls-creds-x509,id=tls0,dir=/home/berrange/qemutls,\
                endpoint=server,verify-peer=yes \
        -object authz-simple,id=acl0,policy=deny,\
                rules.0.match=\*CN=fred,rules.0.policy=allow \
        -chardev socket,host=127.0.0.1,port=9000,server,\
	         tls-creds=tls0,tls-acl=acl0 \
        ...other qemud args...

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 qapi-schema.json |  2 ++
 qemu-char.c      | 11 ++++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/qapi-schema.json b/qapi-schema.json
index 082fcca..5588dbf 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -3222,6 +3222,7 @@
 # @addr: socket address to listen on (server=true)
 #        or connect to (server=false)
 # @tls-creds: #optional the ID of the TLS credentials object (since 2.6)
+# @tls-acl: #optional the ID of the QAuthZ authorization object (since 2.6)
 # @server: #optional create server socket (default: true)
 # @wait: #optional wait for incoming connection on server
 #        sockets (default: false).
@@ -3237,6 +3238,7 @@
 ##
 { 'struct': 'ChardevSocket', 'data': { 'addr'       : 'SocketAddress',
                                      '*tls-creds'  : 'str',
+                                     '*tls-acl'    : 'str',
                                      '*server'    : 'bool',
                                      '*wait'      : 'bool',
                                      '*nodelay'   : 'bool',
diff --git a/qemu-char.c b/qemu-char.c
index b597ee1..e3ced21 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -2604,6 +2604,7 @@ typedef struct {
     QIOChannelSocket *listen_ioc;
     guint listen_tag;
     QCryptoTLSCreds *tls_creds;
+    char *tls_acl;
     int connected;
     int max_size;
     int do_telnetopt;
@@ -3047,7 +3048,7 @@ static void tcp_chr_tls_init(CharDriverState *chr)
     if (s->is_listen) {
         tioc = qio_channel_tls_new_server(
             s->ioc, s->tls_creds,
-            NULL, /* XXX Use an ACL */
+            s->tls_acl,
             &err);
     } else {
         tioc = qio_channel_tls_new_client(
@@ -3169,6 +3170,7 @@ static void tcp_chr_close(CharDriverState *chr)
     if (s->tls_creds) {
         object_unref(OBJECT(s->tls_creds));
     }
+    g_free(s->tls_acl);
     if (s->write_msgfds_num) {
         g_free(s->write_msgfds);
     }
@@ -3668,6 +3670,7 @@ static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
     const char *host = qemu_opt_get(opts, "host");
     const char *port = qemu_opt_get(opts, "port");
     const char *tls_creds = qemu_opt_get(opts, "tls-creds");
+    const char *tls_acl = qemu_opt_get(opts, "tls-acl");
     SocketAddress *addr;
     ChardevSocket *sock;
 
@@ -3701,6 +3704,7 @@ static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
     sock->has_reconnect = true;
     sock->reconnect = reconnect;
     sock->tls_creds = g_strdup(tls_creds);
+    sock->tls_acl = g_strdup(tls_acl);
 
     addr = g_new0(SocketAddress, 1);
     if (path) {
@@ -4155,6 +4159,9 @@ QemuOptsList qemu_chardev_opts = {
             .name = "tls-creds",
             .type = QEMU_OPT_STRING,
         },{
+            .name = "tls-acl",
+            .type = QEMU_OPT_STRING,
+        },{
             .name = "width",
             .type = QEMU_OPT_NUMBER,
         },{
@@ -4398,6 +4405,7 @@ static CharDriverState *qmp_chardev_open_socket(const char *id,
             }
         }
     }
+    s->tls_acl = g_strdup(sock->tls_acl);
 
     qapi_copy_SocketAddress(&s->addr, sock->addr);
 
@@ -4461,6 +4469,7 @@ static CharDriverState *qmp_chardev_open_socket(const char *id,
     if (s->tls_creds) {
         object_unref(OBJECT(s->tls_creds));
     }
+    g_free(s->tls_acl);
     g_free(s);
     qemu_chr_free_common(chr);
     return NULL;
-- 
2.5.5