On Mon, Sep 14, 2026 at 04:38:57PM +0800, Jia Jia wrote:
> >
> > 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.
didn't look into this yet - did u reach any conclusion?
> > > 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
