[Mesa-dev] [PATCH 01/13] glx: Don't create a shared context if the other context isn't the same kind

[Jose Fonseca]

Looks a sensible thing to do.

I assume no DRI driver will ever want to hook vtable->destroy.  If that may eventually happen, then may be it is useful to add an assert(vtable->destroy == dri2_destroy_context) when the context is created.

Jose

----- Original Message -----
> From: Ian Romanick <ian.d.romanick at intel.com>
> 
> Each of the DRI, DRI2, and DRISW backends contain code like the
> following in their create-context routine:
> 
>    if (shareList) {
>       pcp_shared = (struct dri2_context *) shareList;
>       shared = pcp_shared->driContext;
>    }
> 
> This assumes that the glx_context *shareList is actually the correct
> derived type.  However, if shareList was created as an
> indirect-rendering context, it will not be the expected type.  As a
> result, shared will contain garbage.  This garbage will be passed to
> the driver, and the driver will probably segfault.  This can be
> observed with the following GLX code:
> 
>     ctx0 = glXCreateContext(dpy, visinfo, NULL, False);
>     ctx1 = glXCreateContext(dpy, visinfo, ctx0, True);
> 
> Create-context is the only case where this occurs.  All other cases
> where a context is passed to the backend, it is the 'this' pointer
> (i.e., we got to the backend by call something from ctx->vtable).
> 
> To work around this, check that the shareList->vtable->destroy method
> is the same as the destroy method of the expected type.  We could
> also
> check that shareList->vtable matches the vtable or by adding a "tag"
> to glx_context to identify the derived type.
> 
> NOTE: This is a candidate for the 7.11 branch.
> 
> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
> ---
>  src/glx/dri2_glx.c  |    7 +++++++
>  src/glx/dri_glx.c   |    7 +++++++
>  src/glx/drisw_glx.c |    7 +++++++
>  3 files changed, 21 insertions(+), 0 deletions(-)
> 
> diff --git a/src/glx/dri2_glx.c b/src/glx/dri2_glx.c
> index 553869a..f929fdd 100644
> --- a/src/glx/dri2_glx.c
> +++ b/src/glx/dri2_glx.c
> @@ -185,6 +185,13 @@ dri2_create_context(struct glx_screen *base,
>     __DRIcontext *shared = NULL;
>  
>     if (shareList) {
> +      /* If the shareList context is not a DRI2 context, we cannot
> possibly
> +       * create a DRI2 context that shares it.
> +       */
> +      if (shareList->vtable->destroy != dri2_destroy_context) {
> +	 return NULL;
> +      }
> +
>        pcp_shared = (struct dri2_context *) shareList;
>        shared = pcp_shared->driContext;
>     }
> diff --git a/src/glx/dri_glx.c b/src/glx/dri_glx.c
> index 666423a..9365224 100644
> --- a/src/glx/dri_glx.c
> +++ b/src/glx/dri_glx.c
> @@ -587,6 +587,13 @@ dri_create_context(struct glx_screen *base,
>        return NULL;
>  
>     if (shareList) {
> +      /* If the shareList context is not a DRI context, we cannot
> possibly
> +       * create a DRI context that shares it.
> +       */
> +      if (shareList->vtable->destroy != dri_destroy_context) {
> +	 return NULL;
> +      }
> +
>        pcp_shared = (struct dri_context *) shareList;
>        shared = pcp_shared->driContext;
>     }
> diff --git a/src/glx/drisw_glx.c b/src/glx/drisw_glx.c
> index fbc6be2..f988eeb 100644
> --- a/src/glx/drisw_glx.c
> +++ b/src/glx/drisw_glx.c
> @@ -382,6 +382,13 @@ drisw_create_context(struct glx_screen *base,
>        return NULL;
>  
>     if (shareList) {
> +      /* If the shareList context is not a DRISW context, we cannot
> possibly
> +       * create a DRISW context that shares it.
> +       */
> +      if (shareList->vtable->destroy != drisw_destroy_context) {
> +	 return NULL;
> +      }
> +
>        pcp_shared = (struct drisw_context *) shareList;
>        shared = pcp_shared->driContext;
>     }
> --
> 1.7.6.4
> 
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