[Pkg-libvirt-maintainers] Bug#909417: Bug#909417: gtk-vnc: FTBFS randomly (vncconnectiontest fails with "assertion failed")

[Guido Günther]

Hi,
On Thu, Mar 21, 2019 at 12:33:58AM +0100, Steinar H. Gunderson wrote:
> On Sat, Mar 09, 2019 at 07:26:52PM +0100, Santiago Vila wrote:
> > Whoever wants to reproduce this (and possibly debug it), *please*
> > contact me privately and I will gladly provide ssh access to a machine
> > where it happens very often.
> 
> I've looked briefly into this.
> 
> First, to reproduce this reliably, simply restrict it to one core
> (taskset -c 0 /build/gtk3/src/vncconnectiontest). The reason will be fairly
> clear from the text below.
> 
> As far as I can see, this test simulates a broken VNC server (to test the
> client's robustness). It says it's got a 100x100 true color display, but then
> goes on and starts sending a color map.
> 
> As soon as the client receives the information about the color map,
> it realizes something is wrong, and a race starts. Now the client wants to
> close the connection at the same time as the fake server wants to keep
> sending the cmap data. If you've got two cores, the server just keeps on
> sending data happily; by the time it's noticed that the client is gone,
> the test has passed and all is fine. But if you've only got one, then the
> first byte of the cmap causes a context switch over to the client, which then
> gets ample time to read the data and close the socket before the server gets
> to send the next byte. The server thus gets EPIPE, and test_send_u16()
> breaks.
> 
> I believe the right fix is to send every byte after the first “set color map”
> byte using a non-asserting send. When we've done something invalid, we'd
> better be ready for sending data to fail.
> 
> Please try the attached diff; it fixes the problem for me. I can NMU if the
> maintainers want.

I wouldn't mind an NMU.
 -- Guido
> 
> /* Steinar */
> -- 
> Homepage: https://www.sesse.net/

> Index: gtk-vnc-0.9.0/src/vncconnectiontest.c
> ===================================================================
> --- gtk-vnc-0.9.0.orig/src/vncconnectiontest.c
> +++ gtk-vnc-0.9.0/src/vncconnectiontest.c
> @@ -56,12 +56,23 @@ static void test_send_u8(GOutputStream *
>      g_assert(g_output_stream_write_all(os, &v, 1, NULL, NULL, NULL));
>  }
>  
> +static void send_u8(GOutputStream *os, guint8 v)
> +{
> +    g_output_stream_write_all(os, &v, 1, NULL, NULL, NULL);
> +}
> +
>  static void test_send_u16(GOutputStream *os, guint16 v)
>  {
>      v = GUINT16_TO_BE(v);
>      g_assert(g_output_stream_write_all(os, &v, 2, NULL, NULL, NULL));
>  }
>  
> +static void send_u16(GOutputStream *os, guint16 v)
> +{
> +    v = GUINT16_TO_BE(v);
> +    g_output_stream_write_all(os, &v, 2, NULL, NULL, NULL);
> +}
> +
>  static void test_send_u32(GOutputStream *os, guint32 v)
>  {
>      v = GUINT32_TO_BE(v);
> @@ -429,18 +440,18 @@ static void test_unexpected_cmap_server(
>      test_recv_u16(is, 100);
>      test_recv_u16(is, 100);
>  
> -    /* set color map */
> +    /* set color map -- after this, the client may close the connection at any time */
>      test_send_u8(os, 1);
>      /* pad */
> -    test_send_u8(os, 0);
> +    send_u8(os, 0);
>      /* first color, ncolors */
> -    test_send_u16(os, 0);
> -    test_send_u16(os, 1);
> +    send_u16(os, 0);
> +    send_u16(os, 1);
>  
>      /* r,g,b */
> -    test_send_u16(os, 128);
> -    test_send_u16(os, 128);
> -    test_send_u16(os, 128);
> +    send_u16(os, 128);
> +    send_u16(os, 128);
> +    send_u16(os, 128);
>  }
>  
>  
> @@ -505,11 +516,13 @@ static void test_overflow_cmap_server(GI
>      test_send_u16(os, 65535);
>      test_send_u16(os, 2);
>  
> +    /* after this, the client may close the connection at any time */
> +
>      /* r,g,b */
>      for (int i = 0 ; i < 2; i++) {
> -        test_send_u16(os, i);
> -        test_send_u16(os, i);
> -        test_send_u16(os, i);
> +        send_u16(os, i);
> +        send_u16(os, i);
> +        send_u16(os, i);
>      }
>  }
>  

> _______________________________________________
> Pkg-libvirt-maintainers mailing list
> Pkg-libvirt-maintainers at alioth-lists.debian.net
> https://alioth-lists.debian.net/cgi-bin/mailman/listinfo/pkg-libvirt-maintainers