[Spice-devel] [PATCH spice-server v2] Manage lifetime of RedVmcChannel

[Frediano Ziglio]

> 
> Hi,
> 
> On Wed, Nov 02, 2016 at 04:34:47AM -0400, Frediano Ziglio wrote:
> > > 
> > > From: Jonathon Jongsma <jjongsma at redhat.com>
> > > 
> > > Store the channel in the char device object, and unref it in dispose.
> > > Previously, we were just creating a channel and allowing it to leak.
> > > There may be better long-term solutions, but this works for now.
> > > ---
> > >  server/spicevmc.c | 27 ++++++++++++++++++++-------
> > >  1 file changed, 20 insertions(+), 7 deletions(-)
> > > 
> > > Changes:
> > > - squashed fixup.
> > > 
> > > diff --git a/server/spicevmc.c b/server/spicevmc.c
> > > index 7067bc7..a77e868 100644
> > > --- a/server/spicevmc.c
> > > +++ b/server/spicevmc.c
> > > @@ -47,6 +47,9 @@
> > >  #define BUF_SIZE (64 * 1024 + 32)
> > >  #define COMPRESS_THRESHOLD 1000
> > >  
> > > +typedef struct RedVmcChannel RedVmcChannel;
> > > +typedef struct RedVmcChannelClass RedVmcChannelClass;
> > > +
> > >  typedef struct RedVmcPipeItem {
> > >      RedPipeItem base;
> > >  
> > > @@ -75,6 +78,7 @@ typedef struct RedCharDeviceSpiceVmcClass
> > > RedCharDeviceSpiceVmcClass;
> > >  
> > >  struct RedCharDeviceSpiceVmc {
> > >      RedCharDevice parent;
> > > +    RedVmcChannel *channel;
> > >  };
> > >  
> > >  struct RedCharDeviceSpiceVmcClass
> > > @@ -89,9 +93,6 @@ static RedCharDevice
> > > *red_char_device_spicevmc_new(SpiceCharDeviceInstance *sin,
> > >  
> > >  G_DEFINE_TYPE(RedCharDeviceSpiceVmc, red_char_device_spicevmc,
> > >  RED_TYPE_CHAR_DEVICE)
> > >  
> > > -#define RED_CHAR_DEVICE_SPICEVMC_PRIVATE(o) \
> > > -    (G_TYPE_INSTANCE_GET_PRIVATE ((o), RED_TYPE_CHAR_DEVICE_SPICEVMC,
> > > RedCharDeviceSpiceVmcPrivate))
> > > -
> > >  #define RED_TYPE_VMC_CHANNEL red_vmc_channel_get_type()
> > >  
> > >  #define RED_VMC_CHANNEL(obj) \
> > > @@ -103,9 +104,6 @@ G_DEFINE_TYPE(RedCharDeviceSpiceVmc,
> > > red_char_device_spicevmc, RED_TYPE_CHAR_DEV
> > >  #define RED_VMC_CHANNEL_GET_CLASS(obj) \
> > >      (G_TYPE_INSTANCE_GET_CLASS((obj), RED_TYPE_VMC_CHANNEL,
> > >      RedVmcChannelClass))
> > >  
> > > -typedef struct RedVmcChannel RedVmcChannel;
> > > -typedef struct RedVmcChannelClass RedVmcChannelClass;
> > > -
> > >  struct RedVmcChannel
> > >  {
> > >      RedChannel parent;
> > > @@ -855,9 +853,13 @@ RedCharDevice *spicevmc_device_connect(RedsState
> > > *reds,
> > >                                         SpiceCharDeviceInstance *sin,
> > >                                         uint8_t channel_type)
> > >  {
> > > +    RedCharDeviceSpiceVmc *dev_state;
> > >      RedVmcChannel *state = red_vmc_channel_new(reds, channel_type, sin);
> > >  
> > > -    return state->chardev;
> > > +    dev_state = RED_CHAR_DEVICE_SPICEVMC(state->chardev);
> > > +    dev_state->channel = state;
> > > +
> > > +    return RED_CHAR_DEVICE(dev_state);
> > >  }
> > >  
> > >  /* Must be called from RedClient handling thread. */
> > > @@ -904,10 +906,21 @@ SPICE_GNUC_VISIBLE void
> > > spice_server_port_event(SpiceCharDeviceInstance *sin, ui
> > >  }
> > >  
> > >  static void
> > > +red_char_device_spicevmc_dispose(GObject *object)
> > > +{
> > > +    RedCharDeviceSpiceVmc *self = RED_CHAR_DEVICE_SPICEVMC(object);
> > > +
> > > +    g_clear_object(&self->channel);
> >
> > This call produce a double free.
> > The channel is already freed in spicevmc_device_disconnect.
> 
> But g_clear_object() verify if channel is null before the unref and set
> it to NULL afterwards.
> 

Doing a NULL check on a dangling pointer is not much helpful.

> >
> > > +}
> > > +
> > > +static void
> > >  red_char_device_spicevmc_class_init(RedCharDeviceSpiceVmcClass *klass)
> > >  {
> > > +    GObjectClass *object_class = G_OBJECT_CLASS(klass);
> > >      RedCharDeviceClass *char_dev_class = RED_CHAR_DEVICE_CLASS(klass);
> > >
> > > +    object_class->dispose = red_char_device_spicevmc_dispose;
> > > +
> > >      char_dev_class->read_one_msg_from_device =
> > >      spicevmc_chardev_read_msg_from_dev;
> > >      char_dev_class->send_msg_to_client =
> > >      spicevmc_chardev_send_msg_to_client;
> > >      char_dev_class->send_tokens_to_client =
> > >      spicevmc_char_dev_send_tokens_to_client;
> >
> > Removing the double free from this patch will basically revert the
> > entire patch except the RED_CHAR_DEVICE_SPICEVMC_PRIVATE cleanup.
> >

Frediano