[Spice-devel] [spice-gtk v1 1/2] file-xfer: fix segfault on agent disconnection

[Victor Toso]

On Thu, May 12, 2016 at 10:42:37PM +0200, Victor Toso wrote:
> As one can see by the backtrace, the reason for the segfault is that
> g_task_return_now() is called under coroutine context and in
> spice_file_transfer_task_completed() we access memory that the
> coroutine context has no access.
> 
> With GTask integration its callback must respect the coroutine context
> or return-in-idle so the callback can be called in the main context.
> 
> In this specific case the memory access can be fixed also due the
> error that is present which is agent being disconnected during a
> file-xfer. In that situation, we should not try to send a message to
> the agent.
> 
> Program received signal SIGSEGV, Segmentation fault.
> spice_file_transfer_task_completed (self=self at entry=0x7fffd0006f00, error=0x0) at channel-main.c:2963
> 2963            VDAgentFileXferStatusMessage msg = {
> (gdb) bt
>  #0  spice_file_transfer_task_completed (self=self at entry=0x7fffd0006f00, error=0x0) at channel-main.c:2963
>  #1  in file_xfer_data_flushed_cb (source_object=0x7cc1d0, res=0x953390, user_data=user_data at entry=0x7fffd0006f00) at channel-main.c:1857
>  #2  in g_task_return_now (task=0x953390) at gtask.c:1108
>  #3  in g_task_return (task=0x953390, type=<optimized out>) at gtask.c:1166
>  #4  in flush_foreach_remove (key=<optimized out>, value=<optimized out>, user_data=<optimized out>) at channel-main.c:928
>  #5  in g_hash_table_foreach_remove_or_steal (hash_table=0x70cea0, func=func at entry=0x7ffff5616f10 <flush_foreach_remove>, user_data=user_data at entry=0x0, notify=notify at entry=1) at ghash.c:1492
>  #6  in g_hash_table_foreach_remove (hash_table=<optimized out>, func=func at entry=0x7ffff5616f10 <flush_foreach_remove>, user_data=user_data at entry=0x0) at ghash.c:1538
>  #7  in file_xfer_flushed (success=0, channel=0x7cc1d0) at channel-main.c:936
>  #8 _reset_agent (channel=0x7cc1d0) at channel-main.c:466
>  #9 d (channel=0x7cc1d0, connected=connected at entry=0) at channel-main.c:1572

fixed locally the two above:
#8  spice_main_channel_reset_agent (channel=0x7cc1d0) at channel-main.c:466
#9  set_agent_connected (channel=0x7cc1d0, connected=connected at entry=0) at channel-main.c:1572

>  #10 in spice_main_channel_reset (channel=0x7cc1d0, migrating=0) at channel-main.c:485
>  #11 in spice_channel_coroutine (data=0x7cc1d0) at spice-channel.c:2564
>  #12 in coroutine_trampoline (cc=0x7cb860) at coroutine_ucontext.c:63
>  #13 in continuation_trampoline (i0=<optimized out>, i1=<optimized out>) at continuation.c:55
>  #14 in ?? () from /lib64/libc.so.6
>  #15 in ?? ()
>  #16 in ?? ()
> Backtrace stopped: Cannot access memory at address
> ---
>  src/channel-main.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/src/channel-main.c b/src/channel-main.c
> index f7789dd..fb0630e 100644
> --- a/src/channel-main.c
> +++ b/src/channel-main.c
> @@ -2950,6 +2950,8 @@ void spice_main_set_display_enabled(SpiceMainChannel *channel, int id, gboolean
>  static void spice_file_transfer_task_completed(SpiceFileTransferTask *self,
>                                                 GError *error)
>  {
> +    SpiceMainChannelPrivate *main_priv = self->priv->channel->priv;
> +
>      /* In case of multiple errors we only report the first error */
>      if (self->priv->error)
>          g_clear_error(&error);
> @@ -2959,7 +2961,7 @@ static void spice_file_transfer_task_completed(SpiceFileTransferTask *self,
>          self->priv->error = error;
>      }
>  
> -    if (self->priv->error) {
> +    if (self->priv->error && main_priv->agent_connected) {
>          VDAgentFileXferStatusMessage msg = {
>              .id = self->priv->id,
>              .result = error->code == G_IO_ERROR_CANCELLED ?
> -- 
> 2.5.5
> 
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