From 8ead1a8129b42b14a6ccddbf4c24535b3cb80209 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Fri, 9 Jun 2017 22:07:15 +0200 Subject: [PATCH 2/2] nbd: Fix regression on resiliency to port scan RH-Author: Eric Blake Message-id: <20170609220715.29645-3-eblake@redhat.com> Patchwork-id: 75578 O-Subject: [RHEL-7.3.z qemu-kvm PATCH 2/2] nbd: Fix regression on resiliency to port scan Bugzilla: 1460179 RH-Acked-by: Paolo Bonzini RH-Acked-by: Stefan Hajnoczi RH-Acked-by: Thomas Huth 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 commit ee7d7aa 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 commit 1a6245a (a segfault before we could even assert); the (masked) assertion was cleaned up in d3780c2 (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 Message-Id: <20170608222617.20376-1-eblake@redhat.com> (cherry picked from commit ???) https://bugzilla.redhat.com/show_bug.cgi?id=1460179 Signed-off-by: Miroslav Rezanina Conflicts: blockdev-nbd.c - context include/block/nbd.h - context with nbd_client_new parameters, nbd_client_close not static nbd/server.c - in nbd.c instead, context, comment to nbd_client_new matching different parameters qemu-nbd.c - context --- blockdev-nbd.c | 7 ++++++- include/block/nbd.h | 5 +++-- nbd.c | 25 ++++++++++++++++--------- qemu-nbd.c | 4 ++-- 4 files changed, 27 insertions(+), 14 deletions(-) diff --git a/blockdev-nbd.c b/blockdev-nbd.c index 922cf56..dc7cffa 100644 --- a/blockdev-nbd.c +++ b/blockdev-nbd.c @@ -21,6 +21,11 @@ static int server_fd = -1; +static void nbd_blockdev_client_closed(NBDClient *client, bool ignored) +{ + nbd_client_put(client); +} + static void nbd_accept(void *opaque) { struct sockaddr_in addr; @@ -28,7 +33,7 @@ static void nbd_accept(void *opaque) int fd = accept(server_fd, (struct sockaddr *)&addr, &addr_len); if (fd >= 0) { - nbd_client_new(NULL, fd, nbd_client_put); + nbd_client_new(NULL, fd, nbd_blockdev_client_closed); } } diff --git a/include/block/nbd.h b/include/block/nbd.h index 92e360e..963c7ce 100644 --- a/include/block/nbd.h +++ b/include/block/nbd.h @@ -92,8 +92,9 @@ NBDExport *nbd_export_find(const char *name); void nbd_export_set_name(NBDExport *exp, const char *name); void nbd_export_close_all(void); -void nbd_client_new(NBDExport *exp, int csock, void (*close_fn)(NBDClient *)); -void nbd_client_close(NBDClient *client); +void nbd_client_new(NBDExport *exp, int csock, + void (*close_fn)(NBDClient *, bool)); +void nbd_client_close(NBDClient *client, bool negotiated); void nbd_client_get(NBDClient *client); void nbd_client_put(NBDClient *client); diff --git a/nbd.c b/nbd.c index b5cdc1b..c3d554d 100644 --- a/nbd.c +++ b/nbd.c @@ -105,7 +105,7 @@ static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports); struct NBDClient { int refcount; - void (*close)(NBDClient *client); + void (*close_fn)(NBDClient *client, bool negotiated); NBDExport *exp; int sock; @@ -862,7 +862,7 @@ void nbd_client_put(NBDClient *client) } } -void nbd_client_close(NBDClient *client) +void nbd_client_close(NBDClient *client, bool negotiated) { if (client->closing) { return; @@ -876,8 +876,8 @@ void nbd_client_close(NBDClient *client) shutdown(client->sock, 2); /* Also tell the client, so that they release their reference. */ - if (client->close) { - client->close(client); + if (client->close_fn) { + client->close_fn(client, negotiated); } } @@ -964,7 +964,7 @@ void nbd_export_close(NBDExport *exp) nbd_export_get(exp); QTAILQ_FOREACH_SAFE(client, &exp->clients, next, next) { - nbd_client_close(client); + nbd_client_close(client, true); } nbd_export_set_name(exp, NULL); nbd_export_put(exp); @@ -1244,7 +1244,7 @@ done: out: nbd_request_put(req); - nbd_client_close(client); + nbd_client_close(client, true); } static int nbd_can_read(void *opaque) @@ -1285,7 +1285,7 @@ static coroutine_fn void nbd_co_client_start(void *opaque) qemu_set_nonblock(client->sock); qemu_co_mutex_init(&client->send_lock); if (nbd_negotiate(data)) { - nbd_client_close(client); + nbd_client_close(client, false); goto out; } qemu_set_fd_handler2(client->sock, nbd_can_read, nbd_read, NULL, client); @@ -1294,7 +1294,14 @@ out: g_free(data); } -void nbd_client_new(NBDExport *exp, int csock, void (*close_fn)(NBDClient *)) +/* + * Create a new client listener on the given export @exp, using the + * given socket @csock. Begin servicing it in a coroutine. When the + * connection closes, call @close_fn with an indication of whether the + * client completed negotiation. + */ +void nbd_client_new(NBDExport *exp, int csock, + void (*close_fn)(NBDClient *, bool)) { NBDClient *client; NBDClientNewData *data = g_new(NBDClientNewData, 1); @@ -1303,7 +1310,7 @@ void nbd_client_new(NBDExport *exp, int csock, void (*close_fn)(NBDClient *)) client->refcount = 1; client->exp = exp; client->sock = csock; - client->close = close_fn; + client->close_fn = close_fn; data->client = client; data->co = qemu_coroutine_create(nbd_co_client_start); diff --git a/qemu-nbd.c b/qemu-nbd.c index cde7431..e0f4517 100644 --- a/qemu-nbd.c +++ b/qemu-nbd.c @@ -276,10 +276,10 @@ static void nbd_export_closed(NBDExport *exp) state = TERMINATED; } -static void nbd_client_closed(NBDClient *client) +static void nbd_client_closed(NBDClient *client, bool negotiated) { nb_fds--; - if (nb_fds == 0 && !persistent && state == RUNNING) { + if (negotiated && nb_fds == 0 && !persistent && state == RUNNING) { state = TERMINATE; } qemu_notify_event(); -- 1.8.3.1