jbig2_data_in(Jbig2Ctx *ctx, const unsigned char *data, size_t size)
{
    const size_t initial_buf_size = 1024;

    if (ctx->buf == NULL) {
        size_t buf_size = initial_buf_size;

        do
            buf_size <<= 1;
        while (buf_size < size);
        ctx->buf = jbig2_new(ctx, byte, buf_size);
        if (ctx->buf == NULL) {
            return jbig2_error(ctx, JBIG2_SEVERITY_FATAL, -1, "failed to allocate ctx->buf in jbig2_data_in");
        }
        ctx->buf_size = buf_size;
        ctx->buf_rd_ix = 0;
        ctx->buf_wr_ix = 0;
    } else if (ctx->buf_wr_ix + size > ctx->buf_size) {
        if (ctx->buf_rd_ix <= (ctx->buf_size >> 1) && ctx->buf_wr_ix - ctx->buf_rd_ix + size <= ctx->buf_size) {
            memmove(ctx->buf, ctx->buf + ctx->buf_rd_ix, ctx->buf_wr_ix - ctx->buf_rd_ix);
        } else {
            byte *buf;
            size_t buf_size = initial_buf_size;

            do
                buf_size <<= 1;
            while (buf_size < ctx->buf_wr_ix - ctx->buf_rd_ix + size);
            buf = jbig2_new(ctx, byte, buf_size);
            if (buf == NULL) {
                return jbig2_error(ctx, JBIG2_SEVERITY_FATAL, -1, "failed to allocate buf in jbig2_data_in");
            }
            memcpy(buf, ctx->buf + ctx->buf_rd_ix, ctx->buf_wr_ix - ctx->buf_rd_ix);
            jbig2_free(ctx->allocator, ctx->buf);
            ctx->buf = buf;
            ctx->buf_size = buf_size;
        }
        ctx->buf_wr_ix -= ctx->buf_rd_ix;
        ctx->buf_rd_ix = 0;
    }
    memcpy(ctx->buf + ctx->buf_wr_ix, data, size);
    ctx->buf_wr_ix += size;

    /* data has now been added to buffer */

    for (;;) {
        const byte jbig2_id_string[8] = { 0x97, 0x4a, 0x42, 0x32, 0x0d, 0x0a, 0x1a, 0x0a };
        Jbig2Segment *segment;
        size_t header_size;
        int code;

        switch (ctx->state) {
        case JBIG2_FILE_HEADER:
            /* D.4.1 */
            if (ctx->buf_wr_ix - ctx->buf_rd_ix < 9)
                return 0;
            if (memcmp(ctx->buf + ctx->buf_rd_ix, jbig2_id_string, 8))
                return jbig2_error(ctx, JBIG2_SEVERITY_FATAL, -1, "Not a JBIG2 file header");
            /* D.4.2 */
            ctx->file_header_flags = ctx->buf[ctx->buf_rd_ix + 8];
            if (ctx->file_header_flags & 0xFC) {
                jbig2_error(ctx, JBIG2_SEVERITY_WARNING, -1, "reserved bits (2-7) of file header flags are not zero (0x%02x)", ctx->file_header_flags);
            }
            /* D.4.3 */
            if (!(ctx->file_header_flags & 2)) {        /* number of pages is known */
                if (ctx->buf_wr_ix - ctx->buf_rd_ix < 13)
                    return 0;
                ctx->n_pages = jbig2_get_uint32(ctx->buf + ctx->buf_rd_ix + 9);
                ctx->buf_rd_ix += 13;
                if (ctx->n_pages == 1)
                    jbig2_error(ctx, JBIG2_SEVERITY_INFO, -1, "file header indicates a single page document");
                else
                    jbig2_error(ctx, JBIG2_SEVERITY_INFO, -1, "file header indicates a %d page document", ctx->n_pages);
            } else {            /* number of pages not known */

                ctx->n_pages = 0;
                ctx->buf_rd_ix += 9;
            }
            /* determine the file organization based on the flags - D.4.2 again */
            if (ctx->file_header_flags & 1) {
                ctx->state = JBIG2_FILE_SEQUENTIAL_HEADER;
                jbig2_error(ctx, JBIG2_SEVERITY_DEBUG, -1, "file header indicates sequential organization");
            } else {
                ctx->state = JBIG2_FILE_RANDOM_HEADERS;
                jbig2_error(ctx, JBIG2_SEVERITY_DEBUG, -1, "file header indicates random-access organization");

            }
            break;
        case JBIG2_FILE_SEQUENTIAL_HEADER:
        case JBIG2_FILE_RANDOM_HEADERS:
            segment = jbig2_parse_segment_header(ctx, ctx->buf + ctx->buf_rd_ix, ctx->buf_wr_ix - ctx->buf_rd_ix, &header_size);
            if (segment == NULL)
                return 0;       /* need more data */
            ctx->buf_rd_ix += header_size;

            if (ctx->n_segments == ctx->n_segments_max)
                ctx->segments = jbig2_renew(ctx, ctx->segments, Jbig2Segment *, (ctx->n_segments_max <<= 2));

            ctx->segments[ctx->n_segments++] = segment;
            if (ctx->state == JBIG2_FILE_RANDOM_HEADERS) {
                if ((segment->flags & 63) == 51)        /* end of file */
                    ctx->state = JBIG2_FILE_RANDOM_BODIES;
            } else              /* JBIG2_FILE_SEQUENTIAL_HEADER */
                ctx->state = JBIG2_FILE_SEQUENTIAL_BODY;
            break;
        case JBIG2_FILE_SEQUENTIAL_BODY:
        case JBIG2_FILE_RANDOM_BODIES:
            segment = ctx->segments[ctx->segment_index];
            if (segment->data_length > ctx->buf_wr_ix - ctx->buf_rd_ix)
                return 0;       /* need more data */
            code = jbig2_parse_segment(ctx, segment, ctx->buf + ctx->buf_rd_ix);
            ctx->buf_rd_ix += segment->data_length;
            ctx->segment_index++;
            if (ctx->state == JBIG2_FILE_RANDOM_BODIES) {
                if (ctx->segment_index == ctx->n_segments)
                    ctx->state = JBIG2_FILE_EOF;
            } else {            /* JBIG2_FILE_SEQUENCIAL_BODY */

                ctx->state = JBIG2_FILE_SEQUENTIAL_HEADER;
            }
            if (code < 0) {
                ctx->state = JBIG2_FILE_EOF;
                return code;
            }
            break;
        case JBIG2_FILE_EOF:
            if (ctx->buf_rd_ix == ctx->buf_wr_ix)
                return 0;
            return jbig2_error(ctx, JBIG2_SEVERITY_WARNING, -1, "Garbage beyond end of file");
        }
    }
}

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.