static int vqa_decode_chunk(VqaContext *s)
{
    unsigned int chunk_type;
    unsigned int chunk_size;
    int byte_skip;
    unsigned int index = 0;
    int i;
    unsigned char r, g, b;
    int index_shift;
    int res;

    int cbf0_chunk = -1;
    int cbfz_chunk = -1;
    int cbp0_chunk = -1;
    int cbpz_chunk = -1;
    int cpl0_chunk = -1;
    int cplz_chunk = -1;
    int vptz_chunk = -1;

    int x, y;
    int lines = 0;
    int pixel_ptr;
    int vector_index = 0;
    int lobyte = 0;
    int hibyte = 0;
    int lobytes = 0;
    int hibytes = s->decode_buffer_size / 2;

    /* first, traverse through the frame and find the subchunks */
    while (bytestream2_get_bytes_left(&s->gb) >= 8) {

        chunk_type = bytestream2_get_be32u(&s->gb);
        index      = bytestream2_tell(&s->gb);
        chunk_size = bytestream2_get_be32u(&s->gb);

        switch (chunk_type) {

        case CBF0_TAG:
            cbf0_chunk = index;
            break;

        case CBFZ_TAG:
            cbfz_chunk = index;
            break;

        case CBP0_TAG:
            cbp0_chunk = index;
            break;

        case CBPZ_TAG:
            cbpz_chunk = index;
            break;

        case CPL0_TAG:
            cpl0_chunk = index;
            break;

        case CPLZ_TAG:
            cplz_chunk = index;
            break;

        case VPTZ_TAG:
            vptz_chunk = index;
            break;

        default:
            av_log(s->avctx, AV_LOG_ERROR, "  VQA video: Found unknown chunk type: %c%c%c%c (%08X)\n",
            (chunk_type >> 24) & 0xFF,
            (chunk_type >> 16) & 0xFF,
            (chunk_type >>  8) & 0xFF,
            (chunk_type >>  0) & 0xFF,
            chunk_type);
            break;
        }

        byte_skip = chunk_size & 0x01;
        bytestream2_skip(&s->gb, chunk_size + byte_skip);
    }

    /* next, deal with the palette */
    if ((cpl0_chunk != -1) && (cplz_chunk != -1)) {

        /* a chunk should not have both chunk types */
        av_log(s->avctx, AV_LOG_ERROR, "  VQA video: problem: found both CPL0 and CPLZ chunks\n");
        return AVERROR_INVALIDDATA;
    }

    /* decompress the palette chunk */
    if (cplz_chunk != -1) {

/* yet to be handled */

    }

    /* convert the RGB palette into the machine's endian format */
    if (cpl0_chunk != -1) {

        bytestream2_seek(&s->gb, cpl0_chunk, SEEK_SET);
        chunk_size = bytestream2_get_be32(&s->gb);
        /* sanity check the palette size */
        if (chunk_size / 3 > 256 || chunk_size > bytestream2_get_bytes_left(&s->gb)) {
            av_log(s->avctx, AV_LOG_ERROR, "  VQA video: problem: found a palette chunk with %d colors\n",
                chunk_size / 3);
            return AVERROR_INVALIDDATA;
        }
        for (i = 0; i < chunk_size / 3; i++) {
            /* scale by 4 to transform 6-bit palette -> 8-bit */
            r = bytestream2_get_byteu(&s->gb) * 4;
            g = bytestream2_get_byteu(&s->gb) * 4;
            b = bytestream2_get_byteu(&s->gb) * 4;
            s->palette[i] = (r << 16) | (g << 8) | (b);
        }
    }

    /* next, look for a full codebook */
    if ((cbf0_chunk != -1) && (cbfz_chunk != -1)) {

        /* a chunk should not have both chunk types */
        av_log(s->avctx, AV_LOG_ERROR, "  VQA video: problem: found both CBF0 and CBFZ chunks\n");
        return AVERROR_INVALIDDATA;
    }

    /* decompress the full codebook chunk */
    if (cbfz_chunk != -1) {

        bytestream2_seek(&s->gb, cbfz_chunk, SEEK_SET);
        chunk_size = bytestream2_get_be32(&s->gb);
        if ((res = decode_format80(&s->gb, chunk_size, s->codebook,
                                   s->codebook_size, 0)) < 0)
            return res;
    }

    /* copy a full codebook */
    if (cbf0_chunk != -1) {

        bytestream2_seek(&s->gb, cbf0_chunk, SEEK_SET);
        chunk_size = bytestream2_get_be32(&s->gb);
        /* sanity check the full codebook size */
        if (chunk_size > MAX_CODEBOOK_SIZE) {
            av_log(s->avctx, AV_LOG_ERROR, "  VQA video: problem: CBF0 chunk too large (0x%X bytes)\n",
                chunk_size);
            return AVERROR_INVALIDDATA;
        }

        bytestream2_get_buffer(&s->gb, s->codebook, chunk_size);
    }

    /* decode the frame */
    if (vptz_chunk == -1) {

        /* something is wrong if there is no VPTZ chunk */
        av_log(s->avctx, AV_LOG_ERROR, "  VQA video: problem: no VPTZ chunk found\n");
        return AVERROR_INVALIDDATA;
    }

    bytestream2_seek(&s->gb, vptz_chunk, SEEK_SET);
    chunk_size = bytestream2_get_be32(&s->gb);
    if ((res = decode_format80(&s->gb, chunk_size,
                               s->decode_buffer, s->decode_buffer_size, 1)) < 0)
        return res;

    /* render the final PAL8 frame */
    if (s->vector_height == 4)
        index_shift = 4;
    else
        index_shift = 3;
    for (y = 0; y < s->frame.linesize[0] * s->height;
        y += s->frame.linesize[0] * s->vector_height) {

        for (x = y; x < y + s->width; x += 4, lobytes++, hibytes++) {
            pixel_ptr = x;

            /* get the vector index, the method for which varies according to
             * VQA file version */
            switch (s->vqa_version) {

            case 1:
                lobyte = s->decode_buffer[lobytes * 2];
                hibyte = s->decode_buffer[(lobytes * 2) + 1];
                vector_index = ((hibyte << 8) | lobyte) >> 3;
                vector_index <<= index_shift;
                lines = s->vector_height;
                /* uniform color fill - a quick hack */
                if (hibyte == 0xFF) {
                    while (lines--) {
                        s->frame.data[0][pixel_ptr + 0] = 255 - lobyte;
                        s->frame.data[0][pixel_ptr + 1] = 255 - lobyte;
                        s->frame.data[0][pixel_ptr + 2] = 255 - lobyte;
                        s->frame.data[0][pixel_ptr + 3] = 255 - lobyte;
                        pixel_ptr += s->frame.linesize[0];
                    }
                    lines=0;
                }
                break;

            case 2:
                lobyte = s->decode_buffer[lobytes];
                hibyte = s->decode_buffer[hibytes];
                vector_index = (hibyte << 8) | lobyte;
                vector_index <<= index_shift;
                lines = s->vector_height;
                break;

            case 3:
/* not implemented yet */
                lines = 0;
                break;
            }

            while (lines--) {
                s->frame.data[0][pixel_ptr + 0] = s->codebook[vector_index++];
                s->frame.data[0][pixel_ptr + 1] = s->codebook[vector_index++];
                s->frame.data[0][pixel_ptr + 2] = s->codebook[vector_index++];
                s->frame.data[0][pixel_ptr + 3] = s->codebook[vector_index++];
                pixel_ptr += s->frame.linesize[0];
            }
        }
    }

    /* handle partial codebook */
    if ((cbp0_chunk != -1) && (cbpz_chunk != -1)) {
        /* a chunk should not have both chunk types */
        av_log(s->avctx, AV_LOG_ERROR, "  VQA video: problem: found both CBP0 and CBPZ chunks\n");
        return AVERROR_INVALIDDATA;
    }

    if (cbp0_chunk != -1) {

        bytestream2_seek(&s->gb, cbp0_chunk, SEEK_SET);
        chunk_size = bytestream2_get_be32(&s->gb);

        /* accumulate partial codebook */
        bytestream2_get_buffer(&s->gb, &s->next_codebook_buffer[s->next_codebook_buffer_index],
                               chunk_size);
        s->next_codebook_buffer_index += chunk_size;

        s->partial_countdown--;
        if (s->partial_countdown == 0) {

            /* time to replace codebook */
            memcpy(s->codebook, s->next_codebook_buffer,
                s->next_codebook_buffer_index);

            /* reset accounting */
            s->next_codebook_buffer_index = 0;
            s->partial_countdown = s->partial_count;
        }
    }

    if (cbpz_chunk != -1) {

        bytestream2_seek(&s->gb, cbpz_chunk, SEEK_SET);
        chunk_size = bytestream2_get_be32(&s->gb);

        /* accumulate partial codebook */
        bytestream2_get_buffer(&s->gb, &s->next_codebook_buffer[s->next_codebook_buffer_index],
                               chunk_size);
        s->next_codebook_buffer_index += chunk_size;

        s->partial_countdown--;
        if (s->partial_countdown == 0) {
            GetByteContext gb;

            bytestream2_init(&gb, s->next_codebook_buffer, s->next_codebook_buffer_index);
            /* decompress codebook */
            if ((res = decode_format80(&gb, s->next_codebook_buffer_index,
                                       s->codebook, s->codebook_size, 0)) < 0)
                return res;

            /* reset accounting */
            s->next_codebook_buffer_index = 0;
            s->partial_countdown = s->partial_count;
        }
    }

    return 0;
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.