audio/jack: fix use after free segfault

This change registers a bottom handler to close the JACK client
connection when a server shutdown signal is received. Without this
libjack2 attempts to "clean up" old clients and causes a use after free
segfault.

Signed-off-by: Geoffrey McRae <geoff@hostfission.com>
Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <20201108063351.35804-2-geoff@hostfission.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

audio/jackaudio.c

@@ -25,6 +25,7 @@
 #include "qemu/osdep.h"
 #include "qemu/module.h"
 #include "qemu/atomic.h"
+#include "qemu/main-loop.h"
 #include "qemu-common.h"
 #include "audio.h"
 
@@ -63,6 +64,7 @@ typedef struct QJackClient {
     QJackState      state;
     jack_client_t  *client;
     jack_nframes_t  freq;
+    QEMUBH         *shutdown_bh;
 
     struct QJack   *j;
     int             nchannels;
@@ -87,6 +89,7 @@ QJackIn;
 static int qjack_client_init(QJackClient *c);
 static void qjack_client_connect_ports(QJackClient *c);
 static void qjack_client_fini(QJackClient *c);
+static QemuMutex qjack_shutdown_lock;
 
 static void qjack_buffer_create(QJackBuffer *buffer, int channels, int frames)
 {
@@ -306,21 +309,27 @@ static int qjack_xrun(void *arg)
     return 0;
 }
 
+static void qjack_shutdown_bh(void *opaque)
+{
+    QJackClient *c = (QJackClient *)opaque;
+    qjack_client_fini(c);
+}
+
 static void qjack_shutdown(void *arg)
 {
     QJackClient *c = (QJackClient *)arg;
     c->state = QJACK_STATE_SHUTDOWN;
+    qemu_bh_schedule(c->shutdown_bh);
 }
 
 static void qjack_client_recover(QJackClient *c)
 {
-    if (c->state == QJACK_STATE_SHUTDOWN) {
-        qjack_client_fini(c);
+    if (c->state != QJACK_STATE_DISCONNECTED) {
+        return;
     }
 
     /* packets is used simply to throttle this */
-    if (c->state == QJACK_STATE_DISCONNECTED &&
-        c->packets % 100 == 0) {
+    if (c->packets % 100 == 0) {
 
         /* if enabled then attempt to recover */
         if (c->enabled) {
@@ -489,15 +498,16 @@ static int qjack_init_out(HWVoiceOut *hw, struct audsettings *as,
     QJackOut *jo  = (QJackOut *)hw;
     Audiodev *dev = (Audiodev *)drv_opaque;
 
-    qjack_client_fini(&jo->c);
-
     jo->c.out       = true;
     jo->c.enabled   = false;
     jo->c.nchannels = as->nchannels;
     jo->c.opt       = dev->u.jack.out;
 
+    jo->c.shutdown_bh = qemu_bh_new(qjack_shutdown_bh, &jo->c);
+
     int ret = qjack_client_init(&jo->c);
     if (ret != 0) {
+        qemu_bh_delete(jo->c.shutdown_bh);
         return ret;
     }
 
@@ -525,15 +535,16 @@ static int qjack_init_in(HWVoiceIn *hw, struct audsettings *as,
     QJackIn  *ji  = (QJackIn *)hw;
     Audiodev *dev = (Audiodev *)drv_opaque;
 
-    qjack_client_fini(&ji->c);
-
     ji->c.out       = false;
     ji->c.enabled   = false;
     ji->c.nchannels = as->nchannels;
     ji->c.opt       = dev->u.jack.in;
 
+    ji->c.shutdown_bh = qemu_bh_new(qjack_shutdown_bh, &ji->c);
+
     int ret = qjack_client_init(&ji->c);
     if (ret != 0) {
+        qemu_bh_delete(ji->c.shutdown_bh);
         return ret;
     }
 
@@ -555,7 +566,7 @@ static int qjack_init_in(HWVoiceIn *hw, struct audsettings *as,
     return 0;
 }
 
-static void qjack_client_fini(QJackClient *c)
+static void qjack_client_fini_locked(QJackClient *c)
 {
     switch (c->state) {
     case QJACK_STATE_RUNNING:
@@ -564,28 +575,40 @@ static void qjack_client_fini(QJackClient *c)
 
     case QJACK_STATE_SHUTDOWN:
         jack_client_close(c->client);
+        c->client = NULL;
+
+        qjack_buffer_free(&c->fifo);
+        g_free(c->port);
+
+        c->state = QJACK_STATE_DISCONNECTED;
         /* fallthrough */
 
     case QJACK_STATE_DISCONNECTED:
         break;
     }
+}
 
-    qjack_buffer_free(&c->fifo);
-    g_free(c->port);
-
-    c->state = QJACK_STATE_DISCONNECTED;
+static void qjack_client_fini(QJackClient *c)
+{
+    qemu_mutex_lock(&qjack_shutdown_lock);
+    qjack_client_fini_locked(c);
+    qemu_mutex_unlock(&qjack_shutdown_lock);
 }
 
 static void qjack_fini_out(HWVoiceOut *hw)
 {
     QJackOut *jo = (QJackOut *)hw;
     qjack_client_fini(&jo->c);
+
+    qemu_bh_delete(jo->c.shutdown_bh);
 }
 
 static void qjack_fini_in(HWVoiceIn *hw)
 {
     QJackIn *ji = (QJackIn *)hw;
     qjack_client_fini(&ji->c);
+
+    qemu_bh_delete(ji->c.shutdown_bh);
 }
 
 static void qjack_enable_out(HWVoiceOut *hw, bool enable)
@@ -662,6 +685,7 @@ static void qjack_info(const char *msg)
 
 static void register_audio_jack(void)
 {
+    qemu_mutex_init(&qjack_shutdown_lock);
     audio_driver_register(&jack_driver);
     jack_set_thread_creator(qjack_thread_creator);
     jack_set_error_function(qjack_error);