freebsd-dev/sys/xen/xenbus
Roger Pau Monné 4e4e43dc9e 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
2020-12-30 11:18:26 +01:00
..
xenbus_if.m
xenbus.c xen/xenstore: remove unused functions 2020-12-30 11:18:25 +01:00
xenbusb_back.c xen: clean up empty lines in .c and .h files 2020-09-01 21:21:55 +00:00
xenbusb_front.c xen: clean up empty lines in .c and .h files 2020-09-01 21:21:55 +00:00
xenbusb_if.m
xenbusb.c xen: allow limiting the amount of duplicated pending xenstore watches 2020-12-30 11:18:26 +01:00
xenbusb.h xen: clean up empty lines in .c and .h files 2020-09-01 21:21:55 +00:00
xenbusvar.h xen/xenstore: remove unused functions 2020-12-30 11:18:25 +01:00