From 8ead1a8129b42b14a6ccddbf4c24535b3cb80209 Mon Sep 17 00:00:00 2001

From: Eric Blake <eblake@redhat.com>

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 <eblake@redhat.com>

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 <pbonzini@redhat.com>

RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

RH-Acked-by: Thomas Huth <thuth@redhat.com>

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 <eblake@redhat.com>

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 <mrezanin@redhat.com>

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