[Qemu-devel] [PATCH v2 07/10] qemu-nbd: 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 the NBD 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 NBD server. This is still a
fairly weak bar.

This adds a '--tls-acl ACL-ID' option to the qemu-nbd command
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 NBD 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-nbd -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 \
           -tls-creds tls0 \
           -tls-acl acl0
	   ....other qemu-nbd args...

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 qemu-nbd.c    | 13 ++++++++++++-
 qemu-nbd.texi |  4 ++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/qemu-nbd.c b/qemu-nbd.c
index a5c1d95..d70960f 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -42,6 +42,7 @@
 #define QEMU_NBD_OPT_OBJECT        260
 #define QEMU_NBD_OPT_TLSCREDS      261
 #define QEMU_NBD_OPT_IMAGE_OPTS    262
+#define QEMU_NBD_OPT_TLSACL        263
 
 static NBDExport *exp;
 static bool newproto;
@@ -55,6 +56,7 @@ static int nb_fds;
 static QIOChannelSocket *server_ioc;
 static int server_watch = -1;
 static QCryptoTLSCreds *tlscreds;
+static const char *tlsacl;
 
 static void usage(const char *name)
 {
@@ -344,7 +346,7 @@ static gboolean nbd_accept(QIOChannel *ioc, GIOCondition cond, gpointer opaque)
     nb_fds++;
     nbd_update_server_watch();
     nbd_client_new(newproto ? NULL : exp, cioc,
-                   tlscreds, NULL, nbd_client_closed);
+                   tlscreds, tlsacl, nbd_client_closed);
     object_unref(OBJECT(cioc));
 
     return TRUE;
@@ -488,6 +490,7 @@ int main(int argc, char **argv)
         { "export-name", required_argument, NULL, 'x' },
         { "tls-creds", required_argument, NULL, QEMU_NBD_OPT_TLSCREDS },
         { "image-opts", no_argument, NULL, QEMU_NBD_OPT_IMAGE_OPTS },
+        { "tls-acl", no_argument, NULL, QEMU_NBD_OPT_TLSACL },
         { NULL, 0, NULL, 0 }
     };
     int ch;
@@ -689,6 +692,9 @@ int main(int argc, char **argv)
         case QEMU_NBD_OPT_IMAGE_OPTS:
             imageOpts = true;
             break;
+        case QEMU_NBD_OPT_TLSACL:
+            tlsacl = optarg;
+            break;
         }
     }
 
@@ -725,6 +731,11 @@ int main(int argc, char **argv)
                          error_get_pretty(local_err));
             exit(EXIT_FAILURE);
         }
+    } else {
+        if (tlsacl) {
+            error_report("--tls-acl is not permitted without --tls-creds");
+            exit(EXIT_FAILURE);
+        }
     }
 
     if (disconnect) {
diff --git a/qemu-nbd.texi b/qemu-nbd.texi
index 9f23343..69f32cb 100644
--- a/qemu-nbd.texi
+++ b/qemu-nbd.texi
@@ -86,6 +86,10 @@ the new style NBD protocol negotiation
 Enable mandatory TLS encryption for the server by setting the ID
 of the TLS credentials object previously created with the --object
 option.
+@item --tls-acl=ID
+Specify the ID of a qauthz object previously created with the
+--object option. This will be used to authorize users who
+connect against their x509 distinguish name.
 @item -v, --verbose
 Display extra debugging information
 @item -h, --help
-- 
2.5.0