Re: [PATCH v9 1/1] audio/jack: fix use after free segfault

[Christian Schoenebeck]

On Samstag, 7. November 2020 10:58:10 CET Christian Schoenebeck wrote:
> On Samstag, 7. November 2020 01:04:58 CET Geoffrey McRae wrote:
> > This change registers a bottom handler to close the JACK client
> > connection when a server shutdown signal is recieved. Without this

One last minor thing, typo here: "received".

> > libjack2 attempts to "clean up" old clients and causes a use after free
> > segfault.
> > 
> > Signed-off-by: Geoffrey McRae <geoff@hostfission.com>
> > ---
> > 
> >  audio/jackaudio.c | 50 +++++++++++++++++++++++++++++++++++------------
> >  1 file changed, 37 insertions(+), 13 deletions(-)
> > 
> > diff --git a/audio/jackaudio.c b/audio/jackaudio.c
> > index 1e714b30bc..e00e19061a 100644
> > --- a/audio/jackaudio.c
> > +++ b/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);
> > 
> > +QemuMutex qjack_shutdown_lock;
> 
> I think this should be:
> 
> static QemuMutex qjack_shutdown_lock;
> 
> as this mutex is only accessed from within this unit. Except of that:
> 
> Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> 
> BTW it is common practice to add local functions for initializing,
> destroying, locking and unlocking a specific mutex use case to avoid issues
> when code evolves. But so far the use of this mutex is trivial, so it is Ok
> for now from my PoV.
> 
> >  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);
> 
> Best regards,
> Christian Schoenebeck