nbd/server: Plumb in new args to nbd_client_add()

Upcoming patches to fix a CVE need to track an opaque pointer passed
in by the owner of a client object, as well as request for a time
limit on how fast negotiation must complete.  Prepare for that by
changing the signature of nbd_client_new() and adding an accessor to
get at the opaque pointer, although for now the two servers
(qemu-nbd.c and blockdev-nbd.c) do not change behavior even though
they pass in a new default timeout value.

Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-ID: <20240807174943.771624-11-eblake@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
[eblake: s/LIMIT/MAX_SECS/ as suggested by Dan]
Signed-off-by: Eric Blake <eblake@redhat.com>

blockdev-nbd.c

@@ -64,8 +64,10 @@ static void nbd_accept(QIONetListener *listener, QIOChannelSocket *cioc,
     nbd_update_server_watch(nbd_server);
 
     qio_channel_set_name(QIO_CHANNEL(cioc), "nbd-server");
-    nbd_client_new(cioc, nbd_server->tlscreds, nbd_server->tlsauthz,
-                   nbd_blockdev_client_closed);
+    /* TODO - expose handshake timeout as QMP option */
+    nbd_client_new(cioc, NBD_DEFAULT_HANDSHAKE_MAX_SECS,
+                   nbd_server->tlscreds, nbd_server->tlsauthz,
+                   nbd_blockdev_client_closed, NULL);
 }
 
 static void nbd_update_server_watch(NBDServerData *s)

include/block/nbd.h

@@ -33,6 +33,12 @@ typedef struct NBDMetaContexts NBDMetaContexts;
 
 extern const BlockExportDriver blk_exp_nbd;
 
+/*
+ * NBD_DEFAULT_HANDSHAKE_MAX_SECS: Number of seconds in which client must
+ * succeed at NBD_OPT_GO before being forcefully dropped as too slow.
+ */
+#define NBD_DEFAULT_HANDSHAKE_MAX_SECS 10
+
 /* Handshake phase structs - this struct is passed on the wire */
 
 typedef struct NBDOption {
@@ -403,9 +409,12 @@ AioContext *nbd_export_aio_context(NBDExport *exp);
 NBDExport *nbd_export_find(const char *name);
 
 void nbd_client_new(QIOChannelSocket *sioc,
+                    uint32_t handshake_max_secs,
                     QCryptoTLSCreds *tlscreds,
                     const char *tlsauthz,
-                    void (*close_fn)(NBDClient *, bool));
+                    void (*close_fn)(NBDClient *, bool),
+                    void *owner);
+void *nbd_client_owner(NBDClient *client);
 void nbd_client_get(NBDClient *client);
 void nbd_client_put(NBDClient *client);
 

nbd/server.c

@@ -124,12 +124,14 @@ struct NBDMetaContexts {
 struct NBDClient {
     int refcount; /* atomic */
     void (*close_fn)(NBDClient *client, bool negotiated);
+    void *owner;
 
     QemuMutex lock;
 
     NBDExport *exp;
     QCryptoTLSCreds *tlscreds;
     char *tlsauthz;
+    uint32_t handshake_max_secs;
     QIOChannelSocket *sioc; /* The underlying data channel */
     QIOChannel *ioc; /* The current I/O channel which may differ (eg TLS) */
 
@@ -3191,6 +3193,7 @@ static coroutine_fn void nbd_co_client_start(void *opaque)
 
     qemu_co_mutex_init(&client->send_lock);
 
+    /* TODO - utilize client->handshake_max_secs */
     if (nbd_negotiate(client, &local_err)) {
         if (local_err) {
             error_report_err(local_err);
@@ -3205,14 +3208,17 @@ static coroutine_fn void nbd_co_client_start(void *opaque)
 }
 
 /*
- * Create a new client listener using the given channel @sioc.
+ * Create a new client listener using the given channel @sioc and @owner.
  * Begin servicing it in a coroutine.  When the connection closes, call
- * @close_fn with an indication of whether the client completed negotiation.
+ * @close_fn with an indication of whether the client completed negotiation
+ * within @handshake_max_secs seconds (0 for unbounded).
  */
 void nbd_client_new(QIOChannelSocket *sioc,
+                    uint32_t handshake_max_secs,
                     QCryptoTLSCreds *tlscreds,
                     const char *tlsauthz,
-                    void (*close_fn)(NBDClient *, bool))
+                    void (*close_fn)(NBDClient *, bool),
+                    void *owner)
 {
     NBDClient *client;
     Coroutine *co;
@@ -3225,13 +3231,21 @@ void nbd_client_new(QIOChannelSocket *sioc,
         object_ref(OBJECT(client->tlscreds));
     }
     client->tlsauthz = g_strdup(tlsauthz);
+    client->handshake_max_secs = handshake_max_secs;
     client->sioc = sioc;
     qio_channel_set_delay(QIO_CHANNEL(sioc), false);
     object_ref(OBJECT(client->sioc));
     client->ioc = QIO_CHANNEL(sioc);
     object_ref(OBJECT(client->ioc));
     client->close_fn = close_fn;
+    client->owner = owner;
 
     co = qemu_coroutine_create(nbd_co_client_start, client);
     qemu_coroutine_enter(co);
 }
+
+void *
+nbd_client_owner(NBDClient *client)
+{
+    return client->owner;
+}

qemu-nbd.c

@@ -390,7 +390,9 @@ static void nbd_accept(QIONetListener *listener, QIOChannelSocket *cioc,
 
     nb_fds++;
     nbd_update_server_watch();
-    nbd_client_new(cioc, tlscreds, tlsauthz, nbd_client_closed);
+    /* TODO - expose handshake timeout as command line option */
+    nbd_client_new(cioc, NBD_DEFAULT_HANDSHAKE_MAX_SECS,
+                   tlscreds, tlsauthz, nbd_client_closed, NULL);
 }
 
 static void nbd_update_server_watch(void)