From: David Woodhouse Date: Tue, 25 Jul 2023 10:05:00 +0000 (+0200) Subject: hw/xen: prevent guest from binding loopback event channel to itself X-Git-Tag: qemu-xen-4.20.0~605^2~7 X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=75a87af9b228ca7d14902a9390fe5e83c4898eb0;p=qemu-xen.git hw/xen: prevent guest from binding loopback event channel to itself Fuzzing showed that a guest could bind an interdomain port to itself, by guessing the next port to be allocated and putting that as the 'remote' port number. By chance, that works because the newly-allocated port has type EVTCHNSTAT_unbound. It shouldn't. Signed-off-by: David Woodhouse Reviewed-by: Paul Durrant Message-Id: <20230801175747.145906-4-dwmw2@infradead.org> Signed-off-by: Philippe Mathieu-Daudé --- diff --git a/hw/i386/kvm/xen_evtchn.c b/hw/i386/kvm/xen_evtchn.c index 0e9c108614..a731738411 100644 --- a/hw/i386/kvm/xen_evtchn.c +++ b/hw/i386/kvm/xen_evtchn.c @@ -1408,8 +1408,15 @@ int xen_evtchn_bind_interdomain_op(struct evtchn_bind_interdomain *interdomain) XenEvtchnPort *rp = &s->port_table[interdomain->remote_port]; XenEvtchnPort *lp = &s->port_table[interdomain->local_port]; - if (rp->type == EVTCHNSTAT_unbound && rp->type_val == 0) { - /* It's a match! */ + /* + * The 'remote' port for loopback must be an unbound port allocated for + * communication with the local domain (as indicated by rp->type_val + * being zero, not PORT_INFO_TYPEVAL_REMOTE_QEMU), and must *not* be + * the port that was just allocated for the local end. + */ + if (interdomain->local_port != interdomain->remote_port && + rp->type == EVTCHNSTAT_unbound && rp->type_val == 0) { + rp->type = EVTCHNSTAT_interdomain; rp->type_val = interdomain->local_port;