block: pass desired TLS hostname through from block driver client

In

  commit a71d597b98
  Author: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
  Date:   Thu Jun 10 13:08:00 2021 +0300

    block/nbd: reuse nbd_co_do_establish_connection() in nbd_open()

the use of the 'hostname' field from the BDRVNBDState struct was
lost, and 'nbd_connect' just hardcoded it to match the IP socket
address. This was a harmless bug at the time since we block use
with anything other than IP sockets.

Shortly though, we want to allow the caller to override the hostname
used in the TLS certificate checks. This is to allow for TLS
when doing port forwarding or tunneling. Thus we need to reinstate
the passing along of the 'hostname'.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20220304193610.3293146-3-berrange@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

block/nbd.c

@@ -92,7 +92,7 @@ typedef struct BDRVNBDState {
     SocketAddress *saddr;
     char *export, *tlscredsid;
     QCryptoTLSCreds *tlscreds;
-    const char *hostname;
+    const char *tlshostname;
     char *x_dirty_bitmap;
     bool alloc_depth;
 
@@ -1836,7 +1836,7 @@ static int nbd_process_options(BlockDriverState *bs, QDict *options,
             error_setg(errp, "TLS only supported over IP sockets");
             goto error;
         }
-        s->hostname = s->saddr->u.inet.host;
+        s->tlshostname = s->saddr->u.inet.host;
     }
 
     s->x_dirty_bitmap = g_strdup(qemu_opt_get(opts, "x-dirty-bitmap"));
@@ -1876,7 +1876,8 @@ static int nbd_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     s->conn = nbd_client_connection_new(s->saddr, true, s->export,
-                                        s->x_dirty_bitmap, s->tlscreds);
+                                        s->x_dirty_bitmap, s->tlscreds,
+                                        s->tlshostname);
 
     if (s->open_timeout) {
         nbd_client_connection_enable_retry(s->conn);

include/block/nbd.h

@@ -415,7 +415,8 @@ NBDClientConnection *nbd_client_connection_new(const SocketAddress *saddr,
                                                bool do_negotiation,
                                                const char *export_name,
                                                const char *x_dirty_bitmap,
-                                               QCryptoTLSCreds *tlscreds);
+                                               QCryptoTLSCreds *tlscreds,
+                                               const char *tlshostname);
 void nbd_client_connection_release(NBDClientConnection *conn);
 
 QIOChannel *coroutine_fn

nbd/client-connection.c

@@ -33,6 +33,7 @@ struct NBDClientConnection {
     /* Initialization constants, never change */
     SocketAddress *saddr; /* address to connect to */
     QCryptoTLSCreds *tlscreds;
+    char *tlshostname;
     NBDExportInfo initial_info;
     bool do_negotiation;
     bool do_retry;
@@ -77,7 +78,8 @@ NBDClientConnection *nbd_client_connection_new(const SocketAddress *saddr,
                                                bool do_negotiation,
                                                const char *export_name,
                                                const char *x_dirty_bitmap,
-                                               QCryptoTLSCreds *tlscreds)
+                                               QCryptoTLSCreds *tlscreds,
+                                               const char *tlshostname)
 {
     NBDClientConnection *conn = g_new(NBDClientConnection, 1);
 
@@ -85,6 +87,7 @@ NBDClientConnection *nbd_client_connection_new(const SocketAddress *saddr,
     *conn = (NBDClientConnection) {
         .saddr = QAPI_CLONE(SocketAddress, saddr),
         .tlscreds = tlscreds,
+        .tlshostname = g_strdup(tlshostname),
         .do_negotiation = do_negotiation,
 
         .initial_info.request_sizes = true,
@@ -107,6 +110,7 @@ static void nbd_client_connection_do_free(NBDClientConnection *conn)
     }
     error_free(conn->err);
     qapi_free_SocketAddress(conn->saddr);
+    g_free(conn->tlshostname);
     object_unref(OBJECT(conn->tlscreds));
     g_free(conn->initial_info.x_dirty_bitmap);
     g_free(conn->initial_info.name);
@@ -120,6 +124,7 @@ static void nbd_client_connection_do_free(NBDClientConnection *conn)
  */
 static int nbd_connect(QIOChannelSocket *sioc, SocketAddress *addr,
                        NBDExportInfo *info, QCryptoTLSCreds *tlscreds,
+                       const char *tlshostname,
                        QIOChannel **outioc, Error **errp)
 {
     int ret;
@@ -140,7 +145,7 @@ static int nbd_connect(QIOChannelSocket *sioc, SocketAddress *addr,
     }
 
     ret = nbd_receive_negotiate(NULL, QIO_CHANNEL(sioc), tlscreds,
-                                tlscreds ? addr->u.inet.host : NULL,
+                                tlshostname,
                                 outioc, info, errp);
     if (ret < 0) {
         /*
@@ -183,7 +188,8 @@ static void *connect_thread_func(void *opaque)
 
         ret = nbd_connect(conn->sioc, conn->saddr,
                           conn->do_negotiation ? &conn->updated_info : NULL,
-                          conn->tlscreds, &conn->ioc, &local_err);
+                          conn->tlscreds, conn->tlshostname,
+                          &conn->ioc, &local_err);
 
         /*
          * conn->updated_info will finally be returned to the user. Clear the