connection: add sanity check to avoid buffer overflow

[Sergi Granell]

On Thu, 2017-09-14 at 09:21 +0900, Boram Park wrote:
> Before putting data into a buffer, we have to make sure that the data
> size is
> smaller than not only the buffer's full size but also the buffer's empty
> size.
> 
> https://bugs.freedesktop.org/show_bug.cgi?id=102690
> 
> Signed-off-by: Boram Park <boram1288.park at samsung.com>
> Acked-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
> ---
>  src/connection.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/src/connection.c b/src/connection.c
> index 5c3d187..53b1621 100644
> --- a/src/connection.c
> +++ b/src/connection.c
> @@ -63,14 +63,17 @@ struct wl_connection {
>  	int want_flush;
>  };
>  
> +static uint32_t wl_buffer_size(struct wl_buffer *b);
> +

I think it would be a better idea to move the wl_buffer_size definition
at the top to avoid this forward declaration.

>  static int
>  wl_buffer_put(struct wl_buffer *b, const void *data, size_t count)
>  {
> -	uint32_t head, size;
> +	uint32_t head, size, empty;
>  
> -	if (count > sizeof(b->data)) {
> +	empty = sizeof(b->data) - wl_buffer_size(b);
> +	if (count > empty) {
>  		wl_log("Data too big for buffer (%d > %d).\n",
> -		       count, sizeof(b->data));
> +		       count, empty);
>  		errno = E2BIG;
>  		return -1;
>  	}

Other than that,

Reviewed-by: Sergi Granell <xerpi.g.12 at gmail.com>