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![Eric Blake](/assets/img/avatar_default.png)
Back in qemu 2.5, qemu-nbd was immune to port probes (a transient server would not quit, regardless of how many probe connections came and went, until a connection actually negotiated). But we broke that in commitee7d7aa
when removing the return value to nbd_client_new(), although that patch also introduced a bug causing an assertion failure on a client that fails negotiation. We then made it worse during refactoring in commit1a6245a
(a segfault before we could even assert); the (masked) assertion was cleaned up ind3780c2
(still in 2.6), and just recently we finally fixed the segfault ("nbd: Fully intialize client in case of failed negotiation"). But that still means that ever since we added TLS support to qemu-nbd, we have been vulnerable to an ill-timed port-scan being able to cause a denial of service by taking down qemu-nbd before a real client has a chance to connect. Since negotiation is now handled asynchronously via coroutines, we no longer have a synchronous point of return by re-adding a return value to nbd_client_new(). So this patch instead wires things up to pass the negotiation status through the close_fn callback function. Simple test across two terminals: $ qemu-nbd -f raw -p 30001 file $ nmap 127.0.0.1 -p 30001 && \ qemu-io -c 'r 0 512' -f raw nbd://localhost:30001 Note that this patch does not change what constitutes successful negotiation (thus, a client must enter transmission phase before that client can be considered as a reason to terminate the server when the connection ends). Perhaps we may want to tweak things in a later patch to also treat a client that uses NBD_OPT_ABORT as being a 'successful' negotiation (the client correctly talked the NBD protocol, and informed us it was not going to use our export after all), but that's a discussion for another day. Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1451614 Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20170608222617.20376-1-eblake@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
213 lines
5.1 KiB
C
213 lines
5.1 KiB
C
/*
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* Serving QEMU block devices via NBD
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*
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* Copyright (c) 2012 Red Hat, Inc.
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*
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* Author: Paolo Bonzini <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or
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* later. See the COPYING file in the top-level directory.
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*/
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#include "qemu/osdep.h"
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#include "sysemu/blockdev.h"
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#include "sysemu/block-backend.h"
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#include "hw/block/block.h"
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#include "qapi/qmp/qerror.h"
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#include "sysemu/sysemu.h"
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#include "qmp-commands.h"
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#include "block/nbd.h"
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#include "io/channel-socket.h"
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typedef struct NBDServerData {
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QIOChannelSocket *listen_ioc;
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int watch;
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QCryptoTLSCreds *tlscreds;
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} NBDServerData;
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static NBDServerData *nbd_server;
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static void nbd_blockdev_client_closed(NBDClient *client, bool ignored)
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{
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nbd_client_put(client);
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}
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static gboolean nbd_accept(QIOChannel *ioc, GIOCondition condition,
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gpointer opaque)
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{
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QIOChannelSocket *cioc;
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if (!nbd_server) {
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return FALSE;
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}
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cioc = qio_channel_socket_accept(QIO_CHANNEL_SOCKET(ioc),
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NULL);
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if (!cioc) {
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return TRUE;
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}
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qio_channel_set_name(QIO_CHANNEL(cioc), "nbd-server");
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nbd_client_new(NULL, cioc,
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nbd_server->tlscreds, NULL,
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nbd_blockdev_client_closed);
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object_unref(OBJECT(cioc));
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return TRUE;
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}
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static void nbd_server_free(NBDServerData *server)
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{
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if (!server) {
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return;
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}
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if (server->watch != -1) {
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g_source_remove(server->watch);
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}
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object_unref(OBJECT(server->listen_ioc));
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if (server->tlscreds) {
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object_unref(OBJECT(server->tlscreds));
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}
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g_free(server);
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}
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static QCryptoTLSCreds *nbd_get_tls_creds(const char *id, Error **errp)
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{
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Object *obj;
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QCryptoTLSCreds *creds;
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obj = object_resolve_path_component(
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object_get_objects_root(), id);
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if (!obj) {
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error_setg(errp, "No TLS credentials with id '%s'",
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id);
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return NULL;
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}
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creds = (QCryptoTLSCreds *)
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object_dynamic_cast(obj, TYPE_QCRYPTO_TLS_CREDS);
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if (!creds) {
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error_setg(errp, "Object with id '%s' is not TLS credentials",
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id);
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return NULL;
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}
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if (creds->endpoint != QCRYPTO_TLS_CREDS_ENDPOINT_SERVER) {
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error_setg(errp,
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"Expecting TLS credentials with a server endpoint");
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return NULL;
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}
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object_ref(obj);
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return creds;
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}
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void nbd_server_start(SocketAddress *addr, const char *tls_creds,
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Error **errp)
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{
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if (nbd_server) {
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error_setg(errp, "NBD server already running");
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return;
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}
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nbd_server = g_new0(NBDServerData, 1);
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nbd_server->watch = -1;
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nbd_server->listen_ioc = qio_channel_socket_new();
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qio_channel_set_name(QIO_CHANNEL(nbd_server->listen_ioc),
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"nbd-listener");
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if (qio_channel_socket_listen_sync(
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nbd_server->listen_ioc, addr, errp) < 0) {
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goto error;
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}
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if (tls_creds) {
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nbd_server->tlscreds = nbd_get_tls_creds(tls_creds, errp);
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if (!nbd_server->tlscreds) {
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goto error;
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}
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/* TODO SOCKET_ADDRESS_TYPE_FD where fd has AF_INET or AF_INET6 */
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if (addr->type != SOCKET_ADDRESS_TYPE_INET) {
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error_setg(errp, "TLS is only supported with IPv4/IPv6");
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goto error;
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}
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}
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nbd_server->watch = qio_channel_add_watch(
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QIO_CHANNEL(nbd_server->listen_ioc),
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G_IO_IN,
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nbd_accept,
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NULL,
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NULL);
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return;
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error:
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nbd_server_free(nbd_server);
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nbd_server = NULL;
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}
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void qmp_nbd_server_start(SocketAddressLegacy *addr,
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bool has_tls_creds, const char *tls_creds,
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Error **errp)
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{
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SocketAddress *addr_flat = socket_address_flatten(addr);
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nbd_server_start(addr_flat, tls_creds, errp);
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qapi_free_SocketAddress(addr_flat);
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}
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void qmp_nbd_server_add(const char *device, bool has_writable, bool writable,
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Error **errp)
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{
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BlockDriverState *bs = NULL;
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BlockBackend *on_eject_blk;
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NBDExport *exp;
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if (!nbd_server) {
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error_setg(errp, "NBD server not running");
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return;
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}
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if (nbd_export_find(device)) {
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error_setg(errp, "NBD server already exporting device '%s'", device);
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return;
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}
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on_eject_blk = blk_by_name(device);
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bs = bdrv_lookup_bs(device, device, errp);
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if (!bs) {
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return;
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}
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if (!has_writable) {
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writable = false;
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}
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if (bdrv_is_read_only(bs)) {
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writable = false;
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}
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exp = nbd_export_new(bs, 0, -1, writable ? 0 : NBD_FLAG_READ_ONLY,
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NULL, false, on_eject_blk, errp);
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if (!exp) {
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return;
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}
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nbd_export_set_name(exp, device);
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/* The list of named exports has a strong reference to this export now and
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* our only way of accessing it is through nbd_export_find(), so we can drop
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* the strong reference that is @exp. */
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nbd_export_put(exp);
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}
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void qmp_nbd_server_stop(Error **errp)
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{
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nbd_export_close_all();
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nbd_server_free(nbd_server);
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nbd_server = NULL;
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}
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