[PATCH] xfixes: Forbid manipulating clip for source-only pictures (#28968)

[Adam Jackson]

Just throw BadPicture instead of crashing.  It's not currently a
meaningful thing to do anyway, RenderSetPictureRectangles would error if
you tried (which this patch changes to BadPicture as well for
consistency).  The problem with trying to do it is if the clip is
specified as a pixmap then we try to convert it to a region, and
->BitmapToRegion requires a ScreenPtr, and source-only pictures don't
have one.

I can imagine a use for client clip on source-only pictures, so if we
really wanted to allow this, probably the way forward is to always store
the clip as a region internally, and when setting the clip _from_ a
pixmap, look up BitmapToRegion relative to the pixmap not the picture.
But since clearly nobody can be relying on it working...

Signed-off-by: Adam Jackson <ajax at redhat.com>
---
 render/render.c | 2 +-
 xfixes/region.c | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/render/render.c b/render/render.c
index 3b7151a..9ac4a98 100644
--- a/render/render.c
+++ b/render/render.c
@@ -638,7 +638,7 @@ ProcRenderSetPictureClipRectangles(ClientPtr client)
     REQUEST_AT_LEAST_SIZE(xRenderSetPictureClipRectanglesReq);
     VERIFY_PICTURE(pPicture, stuff->picture, client, DixSetAttrAccess);
     if (!pPicture->pDrawable)
-        return BadDrawable;
+        return RenderErrBase + BadPicture;
 
     nr = (client->req_len << 2) - sizeof(xRenderSetPictureClipRectanglesReq);
     if (nr & 4)
diff --git a/xfixes/region.c b/xfixes/region.c
index cc8f1a5..f9de525 100644
--- a/xfixes/region.c
+++ b/xfixes/region.c
@@ -269,6 +269,9 @@ ProcXFixesCreateRegionFromPicture(ClientPtr client)
 
     VERIFY_PICTURE(pPicture, stuff->picture, client, DixGetAttrAccess);
 
+    if (!pPicture->pDrawable)
+        return RenderErrBase + BadPicture;
+
     switch (pPicture->clientClipType) {
     case CT_PIXMAP:
         pRegion = BitmapToRegion(pPicture->pDrawable->pScreen,
@@ -750,6 +753,9 @@ ProcXFixesSetPictureClipRegion(ClientPtr client)
     VERIFY_PICTURE(pPicture, stuff->picture, client, DixSetAttrAccess);
     VERIFY_REGION_OR_NONE(pRegion, stuff->region, client, DixReadAccess);
 
+    if (!pPicture->pDrawable)
+        return RenderErrBase + BadPicture;
+
     return SetPictureClipRegion(pPicture, stuff->xOrigin, stuff->yOrigin,
                                 pRegion);
 }
-- 
1.8.5.3