Commit message: DVB-S2-BB: Prevent infinite loop

Commit 4bf4ee88f0544727e7f89f3f288c6afd2f650a4c removed an else
statement that broke out of the BBFrame processing loop. Without
it, infinite loops might be possible if the GSE frames have bit errors
in the length field.
CVE: CVE-2021-22222
CWE: CWE-835
Vulnerability description: Infinite loop in DVB-S2-BB dissector in Wireshark 3.4.0 to 3.4.5 allows denial of service via packet injection or crafted capture file

Project: wireshark
File: packet-dvb-s2-bb.c

static int dissect_dvb_s2_bb(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_)
{
    proto_item *ti;
    proto_tree *dvb_s2_bb_tree;

    guint8      input8, matype1;
    guint8      sync_flag = 0;
    guint16     input16, bb_data_len = 0, user_packet_length;

    int         sub_dissected        = 0, flag_is_ms = 0, new_off = 0;

    static int * const bb_header_bitfields[] = {
        &hf_dvb_s2_bb_matype1_gs,
        &hf_dvb_s2_bb_matype1_mis,
        &hf_dvb_s2_bb_matype1_acm,
        &hf_dvb_s2_bb_matype1_issyi,
        &hf_dvb_s2_bb_matype1_npd,
        &hf_dvb_s2_bb_matype1_low_ro,
        NULL
    };

    col_append_str(pinfo->cinfo, COL_PROTOCOL, "BB ");
    col_append_str(pinfo->cinfo, COL_INFO, "Baseband ");

    /* create display subtree for the protocol */
    ti = proto_tree_add_item(tree, proto_dvb_s2_bb, tvb, 0, DVB_S2_BB_HEADER_LEN, ENC_NA);
    dvb_s2_bb_tree = proto_item_add_subtree(ti, ett_dvb_s2_bb);

    matype1 = tvb_get_guint8(tvb, DVB_S2_BB_OFFS_MATYPE1);
    new_off += 1;

    if (BIT_IS_CLEAR(matype1, DVB_S2_BB_MIS_POS))
        flag_is_ms = 1;

    proto_tree_add_bitmask_with_flags(dvb_s2_bb_tree, tvb, DVB_S2_BB_OFFS_MATYPE1, hf_dvb_s2_bb_matype1,
        ett_dvb_s2_bb_matype1, bb_header_bitfields, ENC_BIG_ENDIAN, BMT_NO_FLAGS);

    input8 = tvb_get_guint8(tvb, DVB_S2_BB_OFFS_MATYPE1);

    if ((pinfo->fd->num == 1) && (_use_low_rolloff_value != 0)) {
        _use_low_rolloff_value = 0;
    }
    if (((input8 & 0x03) == 3) && !_use_low_rolloff_value) {
      _use_low_rolloff_value = 1;
    }
    if (_use_low_rolloff_value) {
       proto_tree_add_item(dvb_s2_bb_tree, hf_dvb_s2_bb_matype1_low_ro, tvb,
                           DVB_S2_BB_OFFS_MATYPE1, 1, ENC_BIG_ENDIAN);
    } else {
       proto_tree_add_item(dvb_s2_bb_tree, hf_dvb_s2_bb_matype1_high_ro, tvb,
                           DVB_S2_BB_OFFS_MATYPE1, 1, ENC_BIG_ENDIAN);
    }

    input8 = tvb_get_guint8(tvb, DVB_S2_BB_OFFS_MATYPE2);
    new_off += 1;
    if (flag_is_ms) {
        proto_tree_add_uint_format_value(dvb_s2_bb_tree, hf_dvb_s2_bb_matype2, tvb,
                                   DVB_S2_BB_OFFS_MATYPE2, 1, input8, "Input Stream Identifier (ISI): %d",
                                   input8);
    } else {
        proto_tree_add_uint_format_value(dvb_s2_bb_tree, hf_dvb_s2_bb_matype2, tvb,
                                   DVB_S2_BB_OFFS_MATYPE2, 1, input8, "reserved");
    }

    user_packet_length = input16 = tvb_get_ntohs(tvb, DVB_S2_BB_OFFS_UPL);
    new_off += 2;

    proto_tree_add_uint_format(dvb_s2_bb_tree, hf_dvb_s2_bb_upl, tvb,
                               DVB_S2_BB_OFFS_UPL, 2, input16, "User Packet Length: %d bits (%d bytes)",
                               (guint16) input16, (guint16) input16 / 8);

    bb_data_len = input16 = tvb_get_ntohs(tvb, DVB_S2_BB_OFFS_DFL);
    bb_data_len /= 8;
    new_off += 2;

    proto_tree_add_uint_format_value(dvb_s2_bb_tree, hf_dvb_s2_bb_dfl, tvb,
                               DVB_S2_BB_OFFS_DFL, 2, input16, "%d bits (%d bytes)", input16, input16 / 8);

    new_off += 1;
    sync_flag = tvb_get_guint8(tvb, DVB_S2_BB_OFFS_SYNC);
    proto_tree_add_item(dvb_s2_bb_tree, hf_dvb_s2_bb_sync, tvb, DVB_S2_BB_OFFS_SYNC, 1, ENC_BIG_ENDIAN);

    new_off += 2;
    proto_tree_add_item(dvb_s2_bb_tree, hf_dvb_s2_bb_syncd, tvb, DVB_S2_BB_OFFS_SYNCD, 2, ENC_BIG_ENDIAN);

    new_off += 1;
    proto_tree_add_checksum(dvb_s2_bb_tree, tvb, DVB_S2_BB_OFFS_CRC, hf_dvb_s2_bb_crc, hf_dvb_s2_bb_crc_status, &ei_dvb_s2_bb_crc, pinfo,
        compute_crc8(tvb, DVB_S2_BB_HEADER_LEN - 1, 0), ENC_NA, PROTO_CHECKSUM_VERIFY);

    switch (matype1 & DVB_S2_BB_TSGS_MASK) {
    case DVB_S2_BB_TSGS_GENERIC_CONTINUOUS:
        /* Check GSE constraints on the BB header per 9.2.1 of ETSI TS 102 771 */
        if (BIT_IS_SET(matype1, DVB_S2_BB_ISSYI_POS)) {
            expert_add_info(pinfo, ti, &ei_dvb_s2_bb_issy_invalid);
        }
        if (BIT_IS_SET(matype1, DVB_S2_BB_NPD_POS)) {
            expert_add_info(pinfo, ti, &ei_dvb_s2_bb_npd_invalid);
        }
        if (user_packet_length != 0x0000) {
            expert_add_info_format(pinfo, ti, &ei_dvb_s2_bb_upl_invalid,
                "UPL is 0x%04x. It must be 0x0000 for GSE packets.", user_packet_length);
        }


        if (dvb_s2_df_dissection) {
            while (bb_data_len) {
                if (sync_flag == DVB_S2_BB_SYNC_EIP_CRC32 && bb_data_len == DVB_S2_BB_EIP_CRC32_LEN) {
                    proto_tree_add_item(dvb_s2_bb_tree, hf_dvb_s2_bb_eip_crc32, tvb, new_off, bb_data_len, ENC_NA);
                    bb_data_len = 0;
                    new_off += DVB_S2_BB_EIP_CRC32_LEN;
                } else {
                    /* start DVB-GSE dissector */
                    sub_dissected = dissect_dvb_s2_gse(tvb_new_subset_length(tvb, new_off, bb_data_len), pinfo, tree, NULL);
                    new_off += sub_dissected;

                    if ((sub_dissected <= bb_data_len) && (sub_dissected >= DVB_S2_GSE_MINSIZE)) {
                        bb_data_len -= sub_dissected;
                        if (bb_data_len < DVB_S2_GSE_MINSIZE)
                            bb_data_len = 0;
                    }
                }
            }
        } else {
            proto_tree_add_item(dvb_s2_bb_tree, hf_dvb_s2_bb_df, tvb, new_off, bb_data_len, ENC_NA);
            new_off += bb_data_len;
        }
        break;

    case DVB_S2_BB_TSGS_GENERIC_PACKETIZED:
        proto_tree_add_item(tree, hf_dvb_s2_bb_packetized, tvb, new_off, bb_data_len, ENC_NA);
        new_off += bb_data_len;
        break;

    case DVB_S2_BB_TSGS_TRANSPORT_STREAM:
        proto_tree_add_item(tree, hf_dvb_s2_bb_transport, tvb, new_off, bb_data_len, ENC_NA);
        new_off += bb_data_len;
        break;

    default:
        proto_tree_add_item(tree, hf_dvb_s2_bb_reserved, tvb, new_off, bb_data_len, ENC_NA);
        new_off += bb_data_len;
        expert_add_info(pinfo, ti, &ei_dvb_s2_bb_reserved);
        break;
    }

    return new_off;
}