CVE request: kernel: fix soft lockups/OOM issues with unix garbage collector

["Eugene Teo" <eugeneteo () kernel sg>]

This bug is different from CVE-2008-5029, but it can be triggered by
the same reproducers. It requires a CVE name.

"Reported and fixed by Dann Frazier <dannf () hp com>:
This is an implementation of David Miller's suggested fix in:
  https://bugzilla.redhat.com/show_bug.cgi?id=470201

Paraphrasing the description from the above report, it makes sendmsg()
block while UNIX garbage collection is in progress. This avoids a
situation where child processes continue to queue new FDs over a
AF_UNIX socket to a parent
which is in the exit path and running garbage collection on these FDs.
This contention can result in soft lockups and oom-killing of
unrelated processes."

Reproducers:
https://bugzilla.redhat.com/show_bug.cgi?id=470201#c1
https://bugzilla.redhat.com/show_bug.cgi?id=470201#c7

References:
https://bugzilla.redhat.com/show_bug.cgi?id=470201
http://article.gmane.org/gmane.comp.security.oss.general/1223
http://marc.info/?l=linux-netdev&m=122721862313564&w=2
https://bugzilla.redhat.com/show_bug.cgi?id=473259

Patch:
http://marc.info/?l=linux-netdev&m=122771908731133&w=2

Thanks, Eugene