static OPJ_BOOL opj_tcd_code_block_enc_allocate_data(opj_tcd_cblk_enc_t *
        p_code_block)
{
    OPJ_UINT32 l_data_size;

    /* The +1 is needed for https://github.com/uclouvain/openjpeg/issues/835 */
    l_data_size = 1 + (OPJ_UINT32)((p_code_block->x1 - p_code_block->x0) *
                                   (p_code_block->y1 - p_code_block->y0) * (OPJ_INT32)sizeof(OPJ_UINT32));

    if (l_data_size > p_code_block->data_size) {
        if (p_code_block->data) {
            /* We refer to data - 1 since below we incremented it */
            opj_free(p_code_block->data - 1);
        }
        p_code_block->data = (OPJ_BYTE*) opj_malloc(l_data_size + 1);
        if (! p_code_block->data) {
            p_code_block->data_size = 0U;
            return OPJ_FALSE;
        }
        p_code_block->data_size = l_data_size;

        /* We reserve the initial byte as a fake byte to a non-FF value */
        /* and increment the data pointer, so that opj_mqc_init_enc() */
        /* can do bp = data - 1, and opj_mqc_byteout() can safely dereference */
        /* it. */
        p_code_block->data[0] = 0;
        p_code_block->data += 1; /*why +1 ?*/
    }
    return OPJ_TRUE;
}
The software performs operations on a memory buffer, but it can read from or write to a memory location that is outside of the intended boundary of the buffer.