Commit message: None
CVE: CVE-2016-8602
CWE: CWE-704
Vulnerability description: The .sethalftone5 function in psi/zht2.c in Ghostscript before 9.21 allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a crafted Postscript document that calls .sethalftone5 with an empty operand stack.

Project: ghostscript

zsethalftone5(i_ctx_t *i_ctx_p)
{
    os_ptr op = osp;
    uint count;
    gs_halftone_component *phtc = 0;
    gs_halftone_component *pc;
    int code = 0;
    int j;
    bool have_default;
    gs_halftone *pht = 0;
    gx_device_halftone *pdht = 0;
    ref sprocs[GS_CLIENT_COLOR_MAX_COMPONENTS + 1];
    ref tprocs[GS_CLIENT_COLOR_MAX_COMPONENTS + 1];
     gs_memory_t *mem;
     uint edepth = ref_stack_count(&e_stack);
     int npop = 2;
    int dict_enum;
     ref rvalue[2];
     int cname, colorant_number;
     byte * pname;
     uint name_size;
     int halftonetype, type = 0;
     gs_gstate *pgs = igs;
    int space_index;

    if (ref_stack_count(&o_stack) < 2)
        return_error(gs_error_stackunderflow);
    check_type(*op, t_dictionary);
    check_type(*(op - 1), t_dictionary);

    dict_enum = dict_first(op);
    space_index = r_space_index(op - 1);
 
     mem = (gs_memory_t *) idmemory->spaces_indexed[space_index];
     * the device color space, so we need to mark them
     * with a different internal halftone type.
     */
    code = dict_int_param(op - 1, "HalftoneType", 1, 100, 0, &type);
    if (code < 0)
          return code;
    halftonetype = (type == 2 || type == 4)
                        ? ht_type_multiple_colorscreen
                        : ht_type_multiple;

    /* Count how many components that we will actually use. */

    have_default = false;
    for (count = 0; ;) {

        /* Move to next element in the dictionary */
        if ((dict_enum = dict_next(op, dict_enum, rvalue)) == -1)
            break;
        /*
         * Verify that we have a valid component.  We may have a
         * /HalfToneType entry.
         */
        if (!r_has_type(&rvalue[0], t_name))
            continue;
        if (!r_has_type(&rvalue[1], t_dictionary))
            continue;

        /* Get the name of the component  verify that we will use it. */
        cname = name_index(mem, &rvalue[0]);
        code = gs_get_colorname_string(mem, cname, &pname, &name_size);
        if (code < 0)
            break;
        colorant_number = gs_cname_to_colorant_number(pgs, pname, name_size,
                                                halftonetype);
        if (colorant_number < 0)
            continue;
        else if (colorant_number == GX_DEVICE_COLOR_MAX_COMPONENTS) {
            /* If here then we have the "Default" component */
            if (have_default)
                return_error(gs_error_rangecheck);
            have_default = true;
        }

        count++;
        /*
         * Check to see if we have already reached the legal number of
         * components.
         */
        if (count > GS_CLIENT_COLOR_MAX_COMPONENTS + 1) {
            code = gs_note_error(gs_error_rangecheck);
            break;
        }
    }
    if (count == 0 || (halftonetype == ht_type_multiple && ! have_default))
        code = gs_note_error(gs_error_rangecheck);

    if (code >= 0) {
        check_estack(5);		/* for sampling Type 1 screens */
        refset_null(sprocs, count);
        refset_null(tprocs, count);
        rc_alloc_struct_0(pht, gs_halftone, &st_halftone,
                          imemory, pht = 0, ".sethalftone5");
        phtc = gs_alloc_struct_array(mem, count, gs_halftone_component,
                                     &st_ht_component_element,
                                     ".sethalftone5");
        rc_alloc_struct_0(pdht, gx_device_halftone, &st_device_halftone,
                          imemory, pdht = 0, ".sethalftone5");
        if (pht == 0 || phtc == 0 || pdht == 0) {
            j = 0; /* Quiet the compiler:
                      gs_note_error isn't necessarily identity,
                      so j could be left ununitialized. */
            code = gs_note_error(gs_error_VMerror);
        }
    }
    if (code >= 0) {
        dict_enum = dict_first(op);
        for (j = 0, pc = phtc; ;) {
            int type;

            /* Move to next element in the dictionary */
            if ((dict_enum = dict_next(op, dict_enum, rvalue)) == -1)
                break;
            /*
             * Verify that we have a valid component.  We may have a
             * /HalfToneType entry.
             */
            if (!r_has_type(&rvalue[0], t_name))
                continue;
            if (!r_has_type(&rvalue[1], t_dictionary))
                continue;

            /* Get the name of the component */
            cname = name_index(mem, &rvalue[0]);
            code = gs_get_colorname_string(mem, cname, &pname, &name_size);
            if (code < 0)
                break;
            colorant_number = gs_cname_to_colorant_number(pgs, pname, name_size,
                                                halftonetype);
            if (colorant_number < 0)
                continue;		/* Do not use this component */
            pc->cname = cname;
            pc->comp_number = colorant_number;

            /* Now process the component dictionary */
            check_dict_read(rvalue[1]);
            if (dict_int_param(&rvalue[1], "HalftoneType", 1, 7, 0, &type) < 0) {
                code = gs_note_error(gs_error_typecheck);
                break;
            }
            switch (type) {
                default:
                    code = gs_note_error(gs_error_rangecheck);
                    break;
                case 1:
                    code = dict_spot_params(&rvalue[1], &pc->params.spot,
                                                sprocs + j, tprocs + j, mem);
                    pc->params.spot.screen.spot_function = spot1_dummy;
                    pc->type = ht_type_spot;
                    break;
                case 3:
                    code = dict_threshold_params(&rvalue[1], &pc->params.threshold,
                                                        tprocs + j);
                    pc->type = ht_type_threshold;
                    break;
                case 7:
                    code = dict_threshold2_params(&rvalue[1], &pc->params.threshold2,
                                                        tprocs + j, imemory);
                    pc->type = ht_type_threshold2;
                    break;
            }
            if (code < 0)
                break;
            pc++;
            j++;
        }
    }
    if (code >= 0) {
        pht->type = halftonetype;
        pht->params.multiple.components = phtc;
        pht->params.multiple.num_comp = j;
        pht->params.multiple.get_colorname_string = gs_get_colorname_string;
        code = gs_sethalftone_prepare(igs, pht, pdht);
    }
    if (code >= 0) {
        /*
         * Put the actual frequency and angle in the spot function component dictionaries.
         */
        dict_enum = dict_first(op);
        for (pc = phtc; ; ) {
            /* Move to next element in the dictionary */
            if ((dict_enum = dict_next(op, dict_enum, rvalue)) == -1)
                break;

            /* Verify that we have a valid component */
            if (!r_has_type(&rvalue[0], t_name))
                continue;
            if (!r_has_type(&rvalue[1], t_dictionary))
                continue;

            /* Get the name of the component and verify that we will use it. */
            cname = name_index(mem, &rvalue[0]);
            code = gs_get_colorname_string(mem, cname, &pname, &name_size);
            if (code < 0)
                break;
            colorant_number = gs_cname_to_colorant_number(pgs, pname, name_size,
                                                halftonetype);
            if (colorant_number < 0)
                continue;

            if (pc->type == ht_type_spot) {
                code = dict_spot_results(i_ctx_p, &rvalue[1], &pc->params.spot);
                if (code < 0)
                    break;
            }
            pc++;
        }
    }
    if (code >= 0) {
        /*
         * Schedule the sampling of any Type 1 screens,
         * and any (Type 1 or Type 3) TransferFunctions.
         * Save the stack depths in case we have to back out.
         */
        uint odepth = ref_stack_count(&o_stack);
        ref odict, odict5;

        odict = op[-1];
        odict5 = *op;
        pop(2);
        op = osp;
        esp += 5;
        make_mark_estack(esp - 4, es_other, sethalftone_cleanup);
        esp[-3] = odict;
        make_istruct(esp - 2, 0, pht);
        make_istruct(esp - 1, 0, pdht);
        make_op_estack(esp, sethalftone_finish);
        for (j = 0; j < count; j++) {
            gx_ht_order *porder = NULL;

            if (pdht->components == 0)
                porder = &pdht->order;
            else {
                /* Find the component in pdht that matches component j in
                   the pht; gs_sethalftone_prepare() may permute these. */
                int k;
                int comp_number = phtc[j].comp_number;
                for (k = 0; k < count; k++) {
                    if (pdht->components[k].comp_number == comp_number) {
                        porder = &pdht->components[k].corder;
                        break;
                    }
                }
            }
            switch (phtc[j].type) {
            case ht_type_spot:
                code = zscreen_enum_init(i_ctx_p, porder,
                                         &phtc[j].params.spot.screen,
                                         &sprocs[j], 0, 0, space_index);
                if (code < 0)
                    break;
                /* falls through */
            case ht_type_threshold:
                if (!r_has_type(tprocs + j, t__invalid)) {
                    /* Schedule TransferFunction sampling. */
                    /****** check_xstack IS WRONG ******/
                    check_ostack(zcolor_remap_one_ostack);
                    check_estack(zcolor_remap_one_estack);
                    code = zcolor_remap_one(i_ctx_p, tprocs + j,
                                            porder->transfer, igs,
                                            zcolor_remap_one_finish);
                    op = osp;
                }
                break;
            default:	/* not possible here, but to keep */
                                /* the compilers happy.... */
                ;
            }
            if (code < 0) {	/* Restore the stack. */
                ref_stack_pop_to(&o_stack, odepth);
                ref_stack_pop_to(&e_stack, edepth);
                op = osp;
                op[-1] = odict;
                *op = odict5;
                break;
            }
            npop = 0;
        }
    }
    if (code < 0) {
        gs_free_object(mem, pdht, ".sethalftone5");
        gs_free_object(mem, phtc, ".sethalftone5");
        gs_free_object(mem, pht, ".sethalftone5");
        return code;
    }
    pop(npop);
    return (ref_stack_count(&e_stack) > edepth ? o_push_estack : 0);
}