Description:  Frontends can trigger OOM in Backends by update a watched path
References:
 https://xenbits.xen.org/xsa/advisory-349.html
 https://lore.kernel.org/lkml/20201215122606.6874-1-jgross@suse.com/
Notes:
Bugs:
upstream: released (5.11-rc1) [fed1755b118147721f2c87b37b9d66e62c39b668, 2e85d32b1c865bec703ce0c962221a5e955c52c2, be987200fbaceaef340872841d4f7af2c5ee8dc3, 3dc86ca6b4c8cfcba9da7996189d1b5a358a94fc, 9996bd494794a2fe393e97e7a982388c6249aa76]
5.10-upstream-stable: released (5.10.4) [b4898bdd2020bae5391b1667fc6c9e27310c59fe, 9ae6d2f4ca8aa871cbb9c2ab78e1848177c5641c, 6835334e154652858651ac6336e71290e0cc1396, 1a72241aabcbb19b52be6f009423e5782b87a09e, c88347ae936482f079cc17eac405f3f54e839a8d]
4.19-upstream-stable: released (4.19.164) [9039eb22f99545fa80a5897496452cf9962e3289, 3a36e4af694a082ed4273c9e15062677be542a0a, b88c52d02e16cd02e51987646bb662a81f8687a6, 85597c4369c9941dd38e47176ff8b540b2b583a3, be19047894c3715a7ef974849f36cdb5083c4034]
4.9-upstream-stable: released (4.9.250) [7936eefdbec92aaa42281b82c07c6e0b843b7932, a449baadb11bf6c840aba4ab11d075896f088bfc, 1b4681163286f8be68b019c2517d04ddc883f781, c78b43920fe57d40203730c327c7f35f4483af74, 2de7cf2c4b199337a1b71f0b7714f9cd06e64de4]
sid: released (5.9.15-1) [bugfix/all/xen-xenbus-Allow-watches-discard-events-before-queue.patch, bugfix/all/xen-xenbus-Add-will_handle-callback-support-in-xenbu.patch, bugfix/all/xen-xenbus-xen_bus_type-Support-will_handle-watch-ca.patch, bugfix/all/xen-xenbus-Count-pending-messages-for-each-watch.patch, bugfix/all/xenbus-xenbus_backend-Disallow-pending-watch-message.patch]
4.19-buster-security: released (4.19.171-1)
4.9-stretch-security: released (4.9.258-1)