qemu/ui/vnc-jobs.c

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/*
* QEMU VNC display driver
*
* Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws>
* Copyright (C) 2006 Fabrice Bellard
* Copyright (C) 2009 Red Hat, Inc
* Copyright (C) 2010 Corentin Chary <corentin.chary@gmail.com>
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "qemu/osdep.h"
#include "vnc.h"
#include "vnc-jobs.h"
#include "qemu/sockets.h"
#include "qemu/main-loop.h"
#include "block/aio.h"
/*
* Locking:
*
* There are three levels of locking:
* - jobs queue lock: for each operation on the queue (push, pop, isEmpty?)
* - VncDisplay global lock: mainly used for framebuffer updates to avoid
* screen corruption if the framebuffer is updated
* while the worker is doing something.
* - VncState::output lock: used to make sure the output buffer is not corrupted
* if two threads try to write on it at the same time
*
* While the VNC worker thread is working, the VncDisplay global lock is held
* to avoid screen corruption (this does not block vnc_refresh() because it
* uses trylock()) but the output lock is not held because the thread works on
* its own output buffer.
* When the encoding job is done, the worker thread will hold the output lock
* and copy its output buffer in vs->output.
*/
struct VncJobQueue {
QemuCond cond;
QemuMutex mutex;
QemuThread thread;
bool exit;
QTAILQ_HEAD(, VncJob) jobs;
};
typedef struct VncJobQueue VncJobQueue;
/*
* We use a single global queue, but most of the functions are
* already reentrant, so we can easily add more than one encoding thread
*/
static VncJobQueue *queue;
static void vnc_lock_queue(VncJobQueue *queue)
{
qemu_mutex_lock(&queue->mutex);
}
static void vnc_unlock_queue(VncJobQueue *queue)
{
qemu_mutex_unlock(&queue->mutex);
}
VncJob *vnc_job_new(VncState *vs)
{
VncJob *job = g_new0(VncJob, 1);
assert(vs->magic == VNC_MAGIC);
job->vs = vs;
vnc_lock_queue(queue);
QLIST_INIT(&job->rectangles);
vnc_unlock_queue(queue);
return job;
}
int vnc_job_add_rect(VncJob *job, int x, int y, int w, int h)
{
VncRectEntry *entry = g_new0(VncRectEntry, 1);
entry->rect.x = x;
entry->rect.y = y;
entry->rect.w = w;
entry->rect.h = h;
vnc_lock_queue(queue);
QLIST_INSERT_HEAD(&job->rectangles, entry, next);
vnc_unlock_queue(queue);
return 1;
}
void vnc_job_push(VncJob *job)
{
vnc_lock_queue(queue);
if (queue->exit || QLIST_EMPTY(&job->rectangles)) {
g_free(job);
} else {
QTAILQ_INSERT_TAIL(&queue->jobs, job, next);
qemu_cond_broadcast(&queue->cond);
}
vnc_unlock_queue(queue);
}
static bool vnc_has_job_locked(VncState *vs)
{
VncJob *job;
QTAILQ_FOREACH(job, &queue->jobs, next) {
if (job->vs == vs || !vs) {
return true;
}
}
return false;
}
void vnc_jobs_join(VncState *vs)
{
vnc_lock_queue(queue);
while (vnc_has_job_locked(vs)) {
qemu_cond_wait(&queue->cond, &queue->mutex);
}
vnc_unlock_queue(queue);
vnc_jobs_consume_buffer(vs);
}
void vnc_jobs_consume_buffer(VncState *vs)
{
bool flush;
vnc_lock_output(vs);
if (vs->jobs_buffer.offset) {
if (vs->ioc != NULL && buffer_empty(&vs->output)) {
if (vs->ioc_tag) {
g_source_remove(vs->ioc_tag);
}
vnc: fix segfault in closed connection handling On one of our client's node, due to trying to read from closed ioc, a segmentation fault occured. Corresponding backtrace: 0 object_get_class (obj=obj@entry=0x0) 1 qio_channel_readv_full (ioc=0x0, iov=0x7ffe55277180 ... 2 qio_channel_read (ioc=<optimized out> ... 3 vnc_client_read_buf (vs=vs@entry=0x55625f3c6000, ... 4 vnc_client_read_plain (vs=0x55625f3c6000) 5 vnc_client_read (vs=0x55625f3c6000) 6 vnc_client_io (ioc=<optimized out>, condition=G_IO_IN, ... 7 g_main_dispatch (context=0x556251568a50) 8 g_main_context_dispatch (context=context@entry=0x556251568a50) 9 glib_pollfds_poll () 10 os_host_main_loop_wait (timeout=<optimized out>) 11 main_loop_wait (nonblocking=nonblocking@entry=0) 12 main_loop () at vl.c:1909 13 main (argc=<optimized out>, argv=<optimized out>, ... Having analyzed the coredump, I understood that the reason is that ioc_tag is reset on vnc_disconnect_start and ioc is cleaned in vnc_disconnect_finish. Between these two events due to some reasons the ioc_tag was set again and after vnc_disconnect_finish the handler is running with freed ioc, which led to the segmentation fault. The patch checks vs->disconnecting in places where we call qio_channel_add_watch and resets handler if disconnecting == TRUE to prevent such an occurrence. Signed-off-by: Klim Kireev <klim.kireev@virtuozzo.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Message-id: 20180207094844.21402-1-klim.kireev@virtuozzo.com Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
2018-02-07 12:48:44 +03:00
if (vs->disconnecting == FALSE) {
vs->ioc_tag = qio_channel_add_watch(
vs->ioc, G_IO_IN | G_IO_OUT, vnc_client_io, vs, NULL);
}
}
buffer_move(&vs->output, &vs->jobs_buffer);
ui: fix VNC client throttling when forced update is requested The VNC server must throttle data sent to the client to prevent the 'output' buffer size growing without bound, if the client stops reading data off the socket (either maliciously or due to stalled/slow network connection). The current throttling is very crude because it simply checks whether the output buffer offset is zero. This check is disabled if the client has requested a forced update, because we want to send these as soon as possible. As a result, the VNC client can cause QEMU to allocate arbitrary amounts of RAM. They can first start something in the guest that triggers lots of framebuffer updates eg play a youtube video. Then repeatedly send full framebuffer update requests, but never read data back from the server. This can easily make QEMU's VNC server send buffer consume 100MB of RAM per second, until the OOM killer starts reaping processes (hopefully the rogue QEMU process, but it might pick others...). To address this we make the throttling more intelligent, so we can throttle full updates. When we get a forced update request, we keep track of exactly how much data we put on the output buffer. We will not process a subsequent forced update request until this data has been fully sent on the wire. We always allow one forced update request to be in flight, regardless of what data is queued for incremental updates or audio data. The slight complication is that we do not initially know how much data an update will send, as this is done in the background by the VNC job thread. So we must track the fact that the job thread has an update pending, and not process any further updates until this job is has been completed & put data on the output buffer. This unbounded memory growth affects all VNC server configurations supported by QEMU, with no workaround possible. The mitigating factor is that it can only be triggered by a client that has authenticated with the VNC server, and who is able to trigger a large quantity of framebuffer updates or audio samples from the guest OS. Mostly they'll just succeed in getting the OOM killer to kill their own QEMU process, but its possible other processes can get taken out as collateral damage. This is a more general variant of the similar unbounded memory usage flaw in the websockets server, that was previously assigned CVE-2017-15268, and fixed in 2.11 by: commit a7b20a8efa28e5f22c26c06cd06c2f12bc863493 Author: Daniel P. Berrange <berrange@redhat.com> Date: Mon Oct 9 14:43:42 2017 +0100 io: monitor encoutput buffer size from websocket GSource This new general memory usage flaw has been assigned CVE-2017-15124, and is partially fixed by this patch. Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Reviewed-by: Darren Kenny <darren.kenny@oracle.com> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> Message-id: 20171218191228.31018-11-berrange@redhat.com Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
2017-12-18 22:12:25 +03:00
if (vs->job_update == VNC_STATE_UPDATE_FORCE) {
vs->force_update_offset = vs->output.offset;
}
vs->job_update = VNC_STATE_UPDATE_NONE;
}
flush = vs->ioc != NULL && vs->abort != true;
vnc_unlock_output(vs);
if (flush) {
vnc_flush(vs);
}
}
/*
* Copy data for local use
*/
static void vnc_async_encoding_start(VncState *orig, VncState *local)
{
buffer_init(&local->output, "vnc-worker-output");
local->sioc = NULL; /* Don't do any network work on this thread */
local->ioc = NULL; /* Don't do any network work on this thread */
local->vnc_encoding = orig->vnc_encoding;
local->features = orig->features;
local->vd = orig->vd;
local->lossy_rect = orig->lossy_rect;
local->write_pixels = orig->write_pixels;
local->client_pf = orig->client_pf;
local->client_be = orig->client_be;
local->tight = orig->tight;
local->zlib = orig->zlib;
local->hextile = orig->hextile;
local->zrle = orig->zrle;
}
static void vnc_async_encoding_end(VncState *orig, VncState *local)
{
orig->tight = local->tight;
orig->zlib = local->zlib;
orig->hextile = local->hextile;
orig->zrle = local->zrle;
orig->lossy_rect = local->lossy_rect;
}
static int vnc_worker_thread_loop(VncJobQueue *queue)
{
VncJob *job;
VncRectEntry *entry, *tmp;
VncState vs = {};
int n_rectangles;
int saved_offset;
vnc_lock_queue(queue);
while (QTAILQ_EMPTY(&queue->jobs) && !queue->exit) {
qemu_cond_wait(&queue->cond, &queue->mutex);
}
/* Here job can only be NULL if queue->exit is true */
job = QTAILQ_FIRST(&queue->jobs);
vnc_unlock_queue(queue);
assert(job->vs->magic == VNC_MAGIC);
if (queue->exit) {
return -1;
}
vnc_lock_output(job->vs);
if (job->vs->ioc == NULL || job->vs->abort == true) {
vnc_unlock_output(job->vs);
goto disconnected;
}
if (buffer_empty(&job->vs->output)) {
/*
* Looks like a NOP as it obviously moves no data. But it
* moves the empty buffer, so we don't have to malloc a new
* one for vs.output
*/
buffer_move_empty(&vs.output, &job->vs->output);
}
vnc_unlock_output(job->vs);
/* Make a local copy of vs and switch output buffers */
vnc_async_encoding_start(job->vs, &vs);
vs.magic = VNC_MAGIC;
/* Start sending rectangles */
n_rectangles = 0;
vnc_write_u8(&vs, VNC_MSG_SERVER_FRAMEBUFFER_UPDATE);
vnc_write_u8(&vs, 0);
saved_offset = vs.output.offset;
vnc_write_u16(&vs, 0);
vnc_lock_display(job->vs->vd);
QLIST_FOREACH_SAFE(entry, &job->rectangles, next, tmp) {
int n;
if (job->vs->ioc == NULL) {
vnc_unlock_display(job->vs->vd);
/* Copy persistent encoding data */
vnc_async_encoding_end(job->vs, &vs);
goto disconnected;
}
n = vnc_send_framebuffer_update(&vs, entry->rect.x, entry->rect.y,
entry->rect.w, entry->rect.h);
if (n >= 0) {
n_rectangles += n;
}
g_free(entry);
}
vnc_unlock_display(job->vs->vd);
/* Put n_rectangles at the beginning of the message */
vs.output.buffer[saved_offset] = (n_rectangles >> 8) & 0xFF;
vs.output.buffer[saved_offset + 1] = n_rectangles & 0xFF;
vnc_lock_output(job->vs);
if (job->vs->ioc != NULL) {
buffer_move(&job->vs->jobs_buffer, &vs.output);
/* Copy persistent encoding data */
vnc_async_encoding_end(job->vs, &vs);
qemu_bh_schedule(job->vs->bh);
} else {
buffer_reset(&vs.output);
/* Copy persistent encoding data */
vnc_async_encoding_end(job->vs, &vs);
}
vnc_unlock_output(job->vs);
disconnected:
vnc_lock_queue(queue);
QTAILQ_REMOVE(&queue->jobs, job, next);
vnc_unlock_queue(queue);
qemu_cond_broadcast(&queue->cond);
g_free(job);
vs.magic = 0;
return 0;
}
static VncJobQueue *vnc_queue_init(void)
{
VncJobQueue *queue = g_new0(VncJobQueue, 1);
qemu_cond_init(&queue->cond);
qemu_mutex_init(&queue->mutex);
QTAILQ_INIT(&queue->jobs);
return queue;
}
static void vnc_queue_clear(VncJobQueue *q)
{
qemu_cond_destroy(&queue->cond);
qemu_mutex_destroy(&queue->mutex);
g_free(q);
queue = NULL; /* Unset global queue */
}
static void *vnc_worker_thread(void *arg)
{
VncJobQueue *queue = arg;
qemu_thread_get_self(&queue->thread);
while (!vnc_worker_thread_loop(queue)) ;
vnc_queue_clear(queue);
return NULL;
}
static bool vnc_worker_thread_running(void)
{
return queue; /* Check global queue */
}
void vnc_start_worker_thread(void)
{
VncJobQueue *q;
if (vnc_worker_thread_running())
return ;
q = vnc_queue_init();
qemu_thread_create(&q->thread, "vnc_worker", vnc_worker_thread, q,
QEMU_THREAD_DETACHED);
queue = q; /* Set global queue */
}