The branch releng/11.4 has been updated by emaste: URL: https://cgit.FreeBSD.org/src/commit/?id=0279031f358307c4c807dde6be6c08bbb5ec515c
commit 0279031f358307c4c807dde6be6c08bbb5ec515c Author: Roger Pau Monné <[email protected]> AuthorDate: 2020-11-25 11:34:38 +0000 Commit: Ed Maste <[email protected]> CommitDate: 2021-01-29 00:08:11 +0000 xen: allow limiting the amount of duplicated pending xenstore watches Xenstore watches received are queued in a list and processed in a deferred thread. Such queuing was done without any checking, so a guest could potentially trigger a resource starvation against the FreeBSD kernel if such kernel is watching any user-controlled xenstore path. Allowing limiting the amount of pending events a watch can accumulate to prevent a remote guest from triggering this resource starvation issue. For the PV device backends and frontends this limitation is only applied to the other end /state node, which is limited to 1 pending event, the rest of the watched paths can still have unlimited pending watches because they are either local or controlled by a privileged domain. The xenstore user-space device gets special treatment as it's not possible for the kernel to know whether the paths being watched by user-space processes are controlled by a guest domain. For this reason watches set by the xenstore user-space device are limited to 1000 pending events. Note this can be modified using the max_pending_watch_events sysctl of the device. This is XSA-349. Sponsored by: Citrix Systems R&D MFC after: 3 days (cherry picked from commit 4e4e43dc9e1afc863670a031cc5cc75eb5e668d6) Note the xenstore user-space device part of this backport is dropped, as in stable/11 the device doesn't support setting up watches. (cherry picked from commit d9bd043f93df1a31ef16d2198d720a0a0831357f) Approved by: so Security: XSA-349, CVE-2020-29568 --- sys/dev/xen/balloon/balloon.c | 3 ++- sys/dev/xen/blkback/blkback.c | 6 ++++++ sys/dev/xen/control/control.c | 6 ++++++ sys/dev/xen/xenstore/xenstore.c | 14 +++++++++++--- sys/xen/xenbus/xenbusb.c | 17 +++++++++++++++++ sys/xen/xenstore/xenstorevar.h | 9 +++++++++ 6 files changed, 51 insertions(+), 4 deletions(-) diff --git a/sys/dev/xen/balloon/balloon.c b/sys/dev/xen/balloon/balloon.c index aefa5cdb9250..87163000d4a8 100644 --- a/sys/dev/xen/balloon/balloon.c +++ b/sys/dev/xen/balloon/balloon.c @@ -310,7 +310,8 @@ set_new_target(unsigned long target) static struct xs_watch target_watch = { - .node = "memory/target" + .node = "memory/target", + .max_pending = 1, }; /* React to a change in the target key */ diff --git a/sys/dev/xen/blkback/blkback.c b/sys/dev/xen/blkback/blkback.c index a5f9cc101582..4b6eeb0cf62f 100644 --- a/sys/dev/xen/blkback/blkback.c +++ b/sys/dev/xen/blkback/blkback.c @@ -3767,6 +3767,12 @@ xbb_attach(device_t dev) xbb->hotplug_watch.callback = xbb_attach_disk; KASSERT(xbb->hotplug_watch.node == NULL, ("watch node already setup")); xbb->hotplug_watch.node = strdup(sbuf_data(watch_path), M_XENBLOCKBACK); + /* + * We don't care about the path updated, just about the value changes + * on that single node, hence there's no need to queue more that one + * event. + */ + xbb->hotplug_watch.max_pending = 1; sbuf_delete(watch_path); error = xs_register_watch(&xbb->hotplug_watch); if (error != 0) { diff --git a/sys/dev/xen/control/control.c b/sys/dev/xen/control/control.c index d5aa97e03b73..e1739419826b 100644 --- a/sys/dev/xen/control/control.c +++ b/sys/dev/xen/control/control.c @@ -432,6 +432,12 @@ xctrl_attach(device_t dev) xctrl->xctrl_watch.node = "control/shutdown"; xctrl->xctrl_watch.callback = xctrl_on_watch_event; xctrl->xctrl_watch.callback_data = (uintptr_t)xctrl; + /* + * We don't care about the path updated, just about the value changes + * on that single node, hence there's no need to queue more that one + * event. + */ + xctrl->xctrl_watch.max_pending = 1; xs_register_watch(&xctrl->xctrl_watch); if (xen_pv_domain()) diff --git a/sys/dev/xen/xenstore/xenstore.c b/sys/dev/xen/xenstore/xenstore.c index 9289adfc1a79..7cba2a55f973 100644 --- a/sys/dev/xen/xenstore/xenstore.c +++ b/sys/dev/xen/xenstore/xenstore.c @@ -668,12 +668,17 @@ xs_process_msg(enum xsd_sockmsg_type *type) mtx_lock(&xs.registered_watches_lock); msg->u.watch.handle = find_watch( msg->u.watch.vec[XS_WATCH_TOKEN]); - if (msg->u.watch.handle != NULL) { - mtx_lock(&xs.watch_events_lock); + mtx_lock(&xs.watch_events_lock); + if (msg->u.watch.handle != NULL && + (!msg->u.watch.handle->max_pending || + msg->u.watch.handle->pending < + msg->u.watch.handle->max_pending)) { + msg->u.watch.handle->pending++; TAILQ_INSERT_TAIL(&xs.watch_events, msg, list); wakeup(&xs.watch_events); mtx_unlock(&xs.watch_events_lock); } else { + mtx_unlock(&xs.watch_events_lock); free(msg->u.watch.vec, M_XENSTORE); free(msg, M_XENSTORE); } @@ -1045,8 +1050,10 @@ xenwatch_thread(void *unused) mtx_lock(&xs.watch_events_lock); msg = TAILQ_FIRST(&xs.watch_events); - if (msg) + if (msg) { TAILQ_REMOVE(&xs.watch_events, msg, list); + msg->u.watch.handle->pending--; + } mtx_unlock(&xs.watch_events_lock); if (msg != NULL) { @@ -1629,6 +1636,7 @@ xs_register_watch(struct xs_watch *watch) char token[sizeof(watch) * 2 + 1]; int error; + watch->pending = 0; sprintf(token, "%lX", (long)watch); sx_slock(&xs.suspend_mutex); diff --git a/sys/xen/xenbus/xenbusb.c b/sys/xen/xenbus/xenbusb.c index 241efaa8fb4e..f191c7f62311 100644 --- a/sys/xen/xenbus/xenbusb.c +++ b/sys/xen/xenbus/xenbusb.c @@ -702,10 +702,21 @@ xenbusb_add_device(device_t dev, const char *type, const char *id) ivars->xd_otherend_watch.node = statepath; ivars->xd_otherend_watch.callback = xenbusb_otherend_watch_cb; ivars->xd_otherend_watch.callback_data = (uintptr_t)ivars; + /* + * Other end state node watch, limit to one pending event + * to prevent frontends from queuing too many events that + * could cause resource starvation. + */ + ivars->xd_otherend_watch.max_pending = 1; ivars->xd_local_watch.node = ivars->xd_node; ivars->xd_local_watch.callback = xenbusb_local_watch_cb; ivars->xd_local_watch.callback_data = (uintptr_t)ivars; + /* + * Watch our local path, only writable by us or a privileged + * domain, no need to limit. + */ + ivars->xd_local_watch.max_pending = 0; mtx_lock(&xbs->xbs_lock); xbs->xbs_connecting_children++; @@ -764,6 +775,12 @@ xenbusb_attach(device_t dev, char *bus_node, u_int id_components) xbs->xbs_device_watch.node = bus_node; xbs->xbs_device_watch.callback = xenbusb_devices_changed; xbs->xbs_device_watch.callback_data = (uintptr_t)xbs; + /* + * Allow for unlimited pending watches, as those are local paths + * either controlled by the guest or only writable by privileged + * domains. + */ + xbs->xbs_device_watch.max_pending = 0; TASK_INIT(&xbs->xbs_probe_children, 0, xenbusb_probe_children_cb, dev); diff --git a/sys/xen/xenstore/xenstorevar.h b/sys/xen/xenstore/xenstorevar.h index 4c612b4b6881..e58d4e1d5721 100644 --- a/sys/xen/xenstore/xenstorevar.h +++ b/sys/xen/xenstore/xenstorevar.h @@ -72,6 +72,15 @@ struct xs_watch /* Callback client data untouched by the XenStore watch mechanism. */ uintptr_t callback_data; + + /* Maximum number of pending watch events to be delivered. */ + unsigned int max_pending; + + /* + * Private counter used by xenstore to keep track of the pending + * watches. Protected by xs.watch_events_lock. + */ + unsigned int pending; }; LIST_HEAD(xs_watch_list, xs_watch); _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/dev-commits-src-all To unsubscribe, send any mail to "[email protected]"
