static int qcow2_write_snapshots(BlockDriverState *bs)
{
    BDRVQcowState *s = bs->opaque;
    QCowSnapshot *sn;
    QCowSnapshotHeader h;
    QCowSnapshotExtraData extra;
    int i, name_size, id_str_size, snapshots_size;
    struct {
        uint32_t nb_snapshots;
        uint64_t snapshots_offset;
    } QEMU_PACKED header_data;
    int64_t offset, snapshots_offset;
    int ret;

    /* compute the size of the snapshots */
    offset = 0;
    for(i = 0; i < s->nb_snapshots; i++) {
        sn = s->snapshots + i;
        offset = align_offset(offset, 8);
        offset += sizeof(h);
        offset += sizeof(extra);
        offset += strlen(sn->id_str);
        offset += strlen(sn->name);
    }
    snapshots_size = offset;

    /* Allocate space for the new snapshot list */
    snapshots_offset = qcow2_alloc_clusters(bs, snapshots_size);
    offset = snapshots_offset;
    if (offset < 0) {
        ret = offset;
        goto fail;
    }
    ret = bdrv_flush(bs);
    if (ret < 0) {
        goto fail;
    }

    /* The snapshot list position has not yet been updated, so these clusters
     * must indeed be completely free */
    ret = qcow2_pre_write_overlap_check(bs, 0, offset, snapshots_size);
    if (ret < 0) {
        goto fail;
    }


    /* Write all snapshots to the new list */
    for(i = 0; i < s->nb_snapshots; i++) {
        sn = s->snapshots + i;
        memset(&h, 0, sizeof(h));
        h.l1_table_offset = cpu_to_be64(sn->l1_table_offset);
        h.l1_size = cpu_to_be32(sn->l1_size);
        /* If it doesn't fit in 32 bit, older implementations should treat it
         * as a disk-only snapshot rather than truncate the VM state */
        if (sn->vm_state_size <= 0xffffffff) {
            h.vm_state_size = cpu_to_be32(sn->vm_state_size);
        }
        h.date_sec = cpu_to_be32(sn->date_sec);
        h.date_nsec = cpu_to_be32(sn->date_nsec);
        h.vm_clock_nsec = cpu_to_be64(sn->vm_clock_nsec);
        h.extra_data_size = cpu_to_be32(sizeof(extra));

        memset(&extra, 0, sizeof(extra));
        extra.vm_state_size_large = cpu_to_be64(sn->vm_state_size);
        extra.disk_size = cpu_to_be64(sn->disk_size);

        id_str_size = strlen(sn->id_str);
        name_size = strlen(sn->name);
        assert(id_str_size <= UINT16_MAX && name_size <= UINT16_MAX);
        h.id_str_size = cpu_to_be16(id_str_size);
        h.name_size = cpu_to_be16(name_size);
        offset = align_offset(offset, 8);

        ret = bdrv_pwrite(bs->file, offset, &h, sizeof(h));
        if (ret < 0) {
            goto fail;
        }
        offset += sizeof(h);

        ret = bdrv_pwrite(bs->file, offset, &extra, sizeof(extra));
        if (ret < 0) {
            goto fail;
        }
        offset += sizeof(extra);

        ret = bdrv_pwrite(bs->file, offset, sn->id_str, id_str_size);
        if (ret < 0) {
            goto fail;
        }
        offset += id_str_size;

        ret = bdrv_pwrite(bs->file, offset, sn->name, name_size);
        if (ret < 0) {
            goto fail;
        }
        offset += name_size;
    }

    /*
     * Update the header to point to the new snapshot table. This requires the
     * new table and its refcounts to be stable on disk.
     */
    ret = bdrv_flush(bs);
    if (ret < 0) {
        goto fail;
    }

    QEMU_BUILD_BUG_ON(offsetof(QCowHeader, snapshots_offset) !=
        offsetof(QCowHeader, nb_snapshots) + sizeof(header_data.nb_snapshots));

    header_data.nb_snapshots        = cpu_to_be32(s->nb_snapshots);
    header_data.snapshots_offset    = cpu_to_be64(snapshots_offset);

    ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
                           &header_data, sizeof(header_data));
    if (ret < 0) {
        goto fail;
    }

    /* free the old snapshot table */
    qcow2_free_clusters(bs, s->snapshots_offset, s->snapshots_size,
                        QCOW2_DISCARD_SNAPSHOT);
    s->snapshots_offset = snapshots_offset;
    s->snapshots_size = snapshots_size;
    return 0;

fail:
    if (snapshots_offset > 0) {
        qcow2_free_clusters(bs, snapshots_offset, snapshots_size,
                            QCOW2_DISCARD_ALWAYS);
    }
    return ret;
}

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.