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198 lines
6.9 KiB
198 lines
6.9 KiB
From 0c9390d978cbf61e8f16c9f580fa96b305c43568 Mon Sep 17 00:00:00 2001
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From: Eric Blake <eblake@redhat.com>
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Date: Thu, 8 Jun 2017 17:26:17 -0500
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Subject: [PATCH] nbd: Fix regression on resiliency to port scan
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Back in qemu 2.5, qemu-nbd was immune to port probes (a transient
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server would not quit, regardless of how many probe connections
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came and went, until a connection actually negotiated). But we
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broke that in commit ee7d7aa when removing the return value to
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nbd_client_new(), although that patch also introduced a bug causing
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an assertion failure on a client that fails negotiation. We then
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made it worse during refactoring in commit 1a6245a (a segfault
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before we could even assert); the (masked) assertion was cleaned
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up in d3780c2 (still in 2.6), and just recently we finally fixed
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the segfault ("nbd: Fully intialize client in case of failed
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negotiation"). But that still means that ever since we added
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TLS support to qemu-nbd, we have been vulnerable to an ill-timed
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port-scan being able to cause a denial of service by taking down
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qemu-nbd before a real client has a chance to connect.
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Since negotiation is now handled asynchronously via coroutines,
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we no longer have a synchronous point of return by re-adding a
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return value to nbd_client_new(). So this patch instead wires
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things up to pass the negotiation status through the close_fn
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callback function.
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Simple test across two terminals:
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$ qemu-nbd -f raw -p 30001 file
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$ nmap 127.0.0.1 -p 30001 && \
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qemu-io -c 'r 0 512' -f raw nbd://localhost:30001
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Note that this patch does not change what constitutes successful
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negotiation (thus, a client must enter transmission phase before
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that client can be considered as a reason to terminate the server
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when the connection ends). Perhaps we may want to tweak things
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in a later patch to also treat a client that uses NBD_OPT_ABORT
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as being a 'successful' negotiation (the client correctly talked
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the NBD protocol, and informed us it was not going to use our
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export after all), but that's a discussion for another day.
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Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1451614
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Signed-off-by: Eric Blake <eblake@redhat.com>
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Message-Id: <20170608222617.20376-1-eblake@redhat.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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---
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blockdev-nbd.c | 6 +++++-
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include/block/nbd.h | 2 +-
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nbd/server.c | 24 +++++++++++++++---------
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qemu-nbd.c | 4 ++--
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4 files changed, 23 insertions(+), 13 deletions(-)
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diff --git a/blockdev-nbd.c b/blockdev-nbd.c
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index dd0860f4a6..28f551a7b0 100644
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--- a/blockdev-nbd.c
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+++ b/blockdev-nbd.c
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@@ -27,6 +27,10 @@ typedef struct 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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@@ -46,7 +50,7 @@ static gboolean nbd_accept(QIOChannel *ioc, GIOCondition condition,
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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_client_put);
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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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diff --git a/include/block/nbd.h b/include/block/nbd.h
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index 416257abca..8fa5ce51f3 100644
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--- a/include/block/nbd.h
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+++ b/include/block/nbd.h
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@@ -162,7 +162,7 @@ void nbd_client_new(NBDExport *exp,
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QIOChannelSocket *sioc,
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QCryptoTLSCreds *tlscreds,
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const char *tlsaclname,
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- void (*close)(NBDClient *));
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+ void (*close_fn)(NBDClient *, bool));
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void nbd_client_get(NBDClient *client);
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void nbd_client_put(NBDClient *client);
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diff --git a/nbd/server.c b/nbd/server.c
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index 49b55f6ede..f2b1aa47ce 100644
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--- a/nbd/server.c
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+++ b/nbd/server.c
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@@ -81,7 +81,7 @@ static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
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struct NBDClient {
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int refcount;
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- void (*close)(NBDClient *client);
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+ void (*close_fn)(NBDClient *client, bool negotiated);
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bool no_zeroes;
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NBDExport *exp;
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@@ -778,7 +778,7 @@ void nbd_client_put(NBDClient *client)
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}
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}
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-static void client_close(NBDClient *client)
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+static void client_close(NBDClient *client, bool negotiated)
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{
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if (client->closing) {
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return;
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@@ -793,8 +793,8 @@ static void client_close(NBDClient *client)
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NULL);
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/* Also tell the client, so that they release their reference. */
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- if (client->close) {
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- client->close(client);
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+ if (client->close_fn) {
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+ client->close_fn(client, negotiated);
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}
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}
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@@ -975,7 +975,7 @@ void nbd_export_close(NBDExport *exp)
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nbd_export_get(exp);
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QTAILQ_FOREACH_SAFE(client, &exp->clients, next, next) {
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- client_close(client);
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+ client_close(client, true);
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}
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nbd_export_set_name(exp, NULL);
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nbd_export_set_description(exp, NULL);
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@@ -1337,7 +1337,7 @@ done:
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out:
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nbd_request_put(req);
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- client_close(client);
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+ client_close(client, true);
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nbd_client_put(client);
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}
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@@ -1363,7 +1363,7 @@ static coroutine_fn void nbd_co_client_start(void *opaque)
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qemu_co_mutex_init(&client->send_lock);
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if (nbd_negotiate(data)) {
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- client_close(client);
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+ client_close(client, false);
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goto out;
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}
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@@ -1373,11 +1373,17 @@ out:
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g_free(data);
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}
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+/*
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+ * Create a new client listener on the given export @exp, using the
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+ * given channel @sioc. Begin servicing it in a coroutine. When the
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+ * connection closes, call @close_fn with an indication of whether the
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+ * client completed negotiation.
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+ */
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void nbd_client_new(NBDExport *exp,
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QIOChannelSocket *sioc,
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QCryptoTLSCreds *tlscreds,
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const char *tlsaclname,
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- void (*close_fn)(NBDClient *))
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+ void (*close_fn)(NBDClient *, bool))
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{
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NBDClient *client;
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NBDClientNewData *data = g_new(NBDClientNewData, 1);
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@@ -1394,7 +1400,7 @@ void nbd_client_new(NBDExport *exp,
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object_ref(OBJECT(client->sioc));
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client->ioc = QIO_CHANNEL(sioc);
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object_ref(OBJECT(client->ioc));
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- client->close = close_fn;
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+ client->close_fn = close_fn;
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data->client = client;
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data->co = qemu_coroutine_create(nbd_co_client_start, data);
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diff --git a/qemu-nbd.c b/qemu-nbd.c
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index 651f85ecc1..9464a0461c 100644
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--- a/qemu-nbd.c
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+++ b/qemu-nbd.c
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@@ -336,10 +336,10 @@ static void nbd_export_closed(NBDExport *exp)
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static void nbd_update_server_watch(void);
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-static void nbd_client_closed(NBDClient *client)
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+static void nbd_client_closed(NBDClient *client, bool negotiated)
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{
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nb_fds--;
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- if (nb_fds == 0 && !persistent && state == RUNNING) {
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+ if (negotiated && nb_fds == 0 && !persistent && state == RUNNING) {
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state = TERMINATE;
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}
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nbd_update_server_watch();
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--
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2.13.0
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