drm/vmwgfx: Limit the user-space command buffer size

commit 51ab70be upstream.

With older hardware versions, the user could specify arbitrarily large
command buffer sizes, causing a vmalloc / vmap space exhaustion.
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
Signed-off-by: Sinclair Yeh <syeh@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c

@@ -3830,14 +3830,14 @@ static void *vmw_execbuf_cmdbuf(struct vmw_private *dev_priv,
 	int ret;
 
 	*header = NULL;
-	if (!dev_priv->cman || kernel_commands)
-		return kernel_commands;
-
 	if (command_size > SVGA_CB_MAX_SIZE) {
 		DRM_ERROR("Command buffer is too large.\n");
 		return ERR_PTR(-EINVAL);
 	}
 
+	if (!dev_priv->cman || kernel_commands)
+		return kernel_commands;
+
 	/* If possible, add a little space for fencing. */
 	cmdbuf_size = command_size + 512;
 	cmdbuf_size = min_t(size_t, cmdbuf_size, SVGA_CB_MAX_SIZE);