begin_softmask(fz_context *ctx, pdf_run_processor *pr, softmask_save *save)
{
	pdf_gstate *gstate = pr->gstate + pr->gtop;
	pdf_xobject *softmask = gstate->softmask;
	fz_rect mask_bbox;
	fz_matrix tos_save[2], save_ctm;
	fz_matrix mask_matrix;
	fz_colorspace *mask_colorspace;

	save->softmask = softmask;
	if (softmask == NULL)
		return gstate;
	save->page_resources = gstate->softmask_resources;
	save->ctm = gstate->softmask_ctm;
	save_ctm = gstate->ctm;

	pdf_xobject_bbox(ctx, softmask, &mask_bbox);
	pdf_xobject_matrix(ctx, softmask, &mask_matrix);

	pdf_tos_save(ctx, &pr->tos, tos_save);

	if (gstate->luminosity)
		mask_bbox = fz_infinite_rect;
	else
	{
		fz_transform_rect(&mask_bbox, &mask_matrix);
		fz_transform_rect(&mask_bbox, &gstate->softmask_ctm);
	}
	gstate->softmask = NULL;
	gstate->softmask_resources = NULL;
	gstate->ctm = gstate->softmask_ctm;

        mask_colorspace = pdf_xobject_colorspace(ctx, softmask);
 
        if (gstate->luminosity && !mask_colorspace)
               mask_colorspace = fz_device_gray(ctx);
 
        fz_try(ctx)
        {
		fz_begin_mask(ctx, pr->dev, &mask_bbox, gstate->luminosity, mask_colorspace, gstate->softmask_bc, &gstate->fill.color_params);
		pdf_run_xobject(ctx, pr, softmask, save->page_resources, &fz_identity, 1);
	}
	fz_always(ctx)
		fz_drop_colorspace(ctx, mask_colorspace);
	fz_catch(ctx)
	{
		fz_rethrow_if(ctx, FZ_ERROR_TRYLATER);
		/* FIXME: Ignore error - nasty, but if we throw from
		 * here the clip stack would be messed up. */
		/* TODO: pass cookie here to increase the cookie error count */
	}

	fz_end_mask(ctx, pr->dev);

	pdf_tos_restore(ctx, &pr->tos, tos_save);

	gstate = pr->gstate + pr->gtop;
	gstate->ctm = save_ctm;

	return gstate;
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.