[CVE-2011-2484] taskstats: don't allow duplicate entries in listener mode

[Andy Whitcroft]

CVE-2011-2484
	The add_del_listener function in kernel/taskstats.c in the Linux
	kernel 2.6.39.1 and earlier does not prevent multiple registrations
	of exit handlers, which allows local users to cause a denial of
	service (memory and CPU consumption), and bypass the OOM Killer,
	via a crafted application.

The fix for this issue has already hit oneiric via upstream.  Following
this email are two patches, one a backport for hardy, and the other a
clean cherry-pick of the upstream commit for lucid, lucid/fsl-imx51,
maverick, maverick/ti-omap4, natty, and natty/ti-omap4.

Proposing for SRU to hardy, lucid, lucid/fsl-imx51, maverick,
maverick/ti-omap4, natty, and natty/ti-omap4.

-apw