Hi Stefano,
do you might have a chance to look at this Xen patch?
/Christian
On Thursday, 9 July 2026 15:50:36 CEST Christian Schoenebeck wrote:
> The xen-9p disconnect path has two issues:
>
> 1. It frees the Xen9pfsRing structures while in-flight PDUs may still
> reference them via pdu->tag to index rings[]. This causes a UAF
> in xen_9pfs_push_and_notify() when worker threads resume after
> completing filesystem operations.
>
> 2. It never calls v9fs_device_unrealize_common(), which means server
> state (struct LocalData, mountfd, FIDs) is never cleaned up on
> disconnect, causing a resource leak on every guest-initiated
> disconnect.
>
> Fix both by draining in-flight PDUs via v9fs_reset() before tearing
> down rings, and calling v9fs_device_unrealize_common() to clean up
> server state.
>
> Fixes: b37eeb0201 ("xen/9pfs: introduce Xen 9pfs backend")
> Signed-off-by: Christian Schoenebeck <[email protected]>
> ---
> hw/9pfs/xen-9p-backend.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/hw/9pfs/xen-9p-backend.c b/hw/9pfs/xen-9p-backend.c
> index 24c90d97ec..3b7a68779a 100644
> --- a/hw/9pfs/xen-9p-backend.c
> +++ b/hw/9pfs/xen-9p-backend.c
> @@ -368,10 +368,14 @@ static void xen_9pfs_evtchn_event(void *opaque)
> static void xen_9pfs_disconnect(struct XenLegacyDevice *xendev)
> {
> Xen9pfsDev *xen_9pdev = container_of(xendev, Xen9pfsDev, xendev);
> + V9fsState *s = &xen_9pdev->state;
> int i;
>
> trace_xen_9pfs_disconnect(xendev->name);
>
> + v9fs_reset(s);
> + v9fs_device_unrealize_common(s);
> +
> for (i = 0; i < xen_9pdev->num_rings; i++) {
> if (xen_9pdev->rings[i].evtchndev != NULL) {
>
> qemu_set_fd_handler(qemu_xen_evtchn_fd(xen_9pdev->rings[i].evtchndev),
