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    SubjectRe: [PATCH RFC v2 08/10] vdpa: add vdpa simulator for block device
    On Tue, Feb 02, 2021 at 09:34:12AM +0000, Stefan Hajnoczi wrote:
    >On Thu, Jan 28, 2021 at 03:41:25PM +0100, Stefano Garzarella wrote:
    >> +static void vdpasim_blk_work(struct work_struct *work)
    >> +{
    >> + struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
    >> + u8 status = VIRTIO_BLK_S_OK;
    >> + int i;
    >> +
    >> + spin_lock(&vdpasim->lock);
    >> +
    >> + if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
    >> + goto out;
    >> +
    >> + for (i = 0; i < VDPASIM_BLK_VQ_NUM; i++) {
    >> + struct vdpasim_virtqueue *vq = &vdpasim->vqs[i];
    >> +
    >> + if (!vq->ready)
    >> + continue;
    >> +
    >> + while (vringh_getdesc_iotlb(&vq->vring, &vq->out_iov,
    >> + &vq->in_iov, &vq->head,
    >> + GFP_ATOMIC) > 0) {
    >> + int write;
    >> +
    >> + vq->in_iov.i = vq->in_iov.used - 1;
    >> + write = vringh_iov_push_iotlb(&vq->vring, &vq->in_iov,
    >> + &status, 1);
    >> + if (write <= 0)
    >> + break;
    >
    >This code looks fragile:
    >
    >1. Relying on unsigned underflow and the while loop in
    > vringh_iov_push_iotlb() to handle the case where in_iov.used == 0 is
    > risky and could break.
    >
    >2. Does this assume that the last in_iov element has size 1? For
    > example, the guest driver may send a single "in" iovec with size 513
    > when reading 512 bytes (with an extra byte for the request status).
    >
    >Please validate inputs fully, even in test/development code, because
    >it's likely to be copied by others when writing production code (or
    >deployed in production by unsuspecting users) :).

    Perfectly agree on that, so I addressed these things, also following
    your review on the previous version, on the next patch of this series:
    "vdpa_sim_blk: implement ramdisk behaviour".

    Do you think should I move these checks in this patch?

    I did this to leave Max credit for this patch and add more code to
    emulate a ramdisk in later patches.

    Thanks,
    Stefano

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