>
> Thank you for your contribution! Sashiko AI review found 2 potential issue(s)
> to consider:
>
> Pre-existing issues:
> - [Critical] vhost_scsi_do_evt_work() accesses vq->iov[out] without verifying
> that the guest actually provided an input buffer, leading to arbitrary
> user-space memory corruption.
> - [High] Events are processed in LIFO order instead of FIFO, which can cause
> state corruption for hotplug/hotunplug sequences.
> --
>
> commit 05830c30fc2e4dc682c270a9b487ae5abb66218b
> Author: Jia Jia <[email protected]>
>
> vhost-scsi: do not relock event vq mutex on send_evt fallback
>
> This commit resolves a deadlock during fallback event handling when the vhost
> worker has disconnected. It splits event completion into an internal unlocked
> helper and a locked wrapper to safely reuse the completion path.
>
> Link: https://lore.kernel.org/all/[email protected]/
>
> > diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> > index 4f8c0260bc9e7..42abf18291b75 100644
> > --- a/drivers/vhost/scsi.c
> > +++ b/drivers/vhost/scsi.c
> > @@ -660,19 +660,26 @@ vhost_scsi_do_evt_work(struct vhost_scsi *vs, struct
> > vhost_scsi_evt *evt)
> > vhost_scsi_log_write(vq, vq_log, log_num);
> > }
> >
> > -static void vhost_scsi_complete_events(struct vhost_scsi *vs, bool drop)
> > +/* Caller must hold the event virtqueue mutex. */
> > +static void __vhost_scsi_complete_events(struct vhost_scsi *vs, bool drop)
> > {
> > - struct vhost_virtqueue *vq = &vs->vqs[VHOST_SCSI_VQ_EVT].vq;
> > struct vhost_scsi_evt *evt, *t;
> > struct llist_node *llnode;
> >
> > - mutex_lock(&vq->mutex);
> > llnode = llist_del_all(&vs->vs_event_list);
> > llist_for_each_entry_safe(evt, t, llnode, list) {
>
> [Severity: High]
> This is a pre-existing issue, but does this loop deliver events to the guest
> in reverse order?
>
> The events are added to vs_event_list using llist_add(), which constructs a
> last-in, first-out list. Because lnode is retrieved locklessly with
> llist_del_all(), and the iteration happens without first calling
> llist_reverse_order(), the events appear to be processed from newest to
> oldest.
>
> Could this cause state corruption for hotplug and hotunplug sequences? For
> example, if a device is plugged and then rapidly unplugged, the guest might
> receive the unplug event first and the plug event second, leaving it
> erroneously believing the device is still present.
>
Looks like this could get the acquire order wrong? Need to verify.
> > if (!drop)
> > vhost_scsi_do_evt_work(vs, evt);
>
> [Severity: Critical]
> This is a pre-existing issue, but can this function access out-of-bounds or
> stale memory if the guest provides an empty input buffer?
>
> Looking at vhost_scsi_do_evt_work() in drivers/vhost/scsi.c, the code uses
> vhost_get_vq_desc() which populates vq->iov:
>
> head = vhost_get_vq_desc(vq, vq->iov,
> ARRAY_SIZE(vq->iov), &out, &in,
> vq_log, &log_num);
> ...
> if ((vq->iov[out].iov_len != sizeof(struct virtio_scsi_event))) {
> vq_err(vq, "Expecting virtio_scsi_event, got %zu bytes\n",
> vq->iov[out].iov_len);
>
> If a guest submits a descriptor chain with only read-only descriptors,
> vhost_get_vq_desc() sets in = 0. The out variable holds the count of
> read-only descriptors, meaning the first writable descriptor expected by the
> host would be at index out.
>
This is a dup -- an earlier patch already fixed it:
https://lore.kernel.org/all/[email protected]/
It was while fixing that earlier issue that Sashiko spotted this
adjacent problem.
> Does the length check above access vq->iov[out].iov_len without verifying
> that in > 0?
>
> If in is 0, vq->iov[out] was not populated by vhost_get_vq_desc() and
> contains stale data from a previous request. Could a malicious guest use
> this to force the kernel to write the event structure to a previously
> legitimate but now hot-unplugged host virtual address via the
> __copy_to_user() call later in the function?
>
> > vhost_scsi_free_evt(vs, evt);
> > }
> > +}
>
> [ ... ]
>
> --
> Sashiko AI review ยท
> https://sashiko.dev/#/patchset/[email protected]?part=1
