linux-kernel - drop SECURITY_FILE

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Date:	Tue, 10 Nov 2009 08:07:39 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	linux-security-module@...r.kernel.org,
	Andrew Morgan <morgan@...nel.org>,
	Steve Grubb <sgrubb@...hat.com>,
	Kees Cook <kees.cook@...onical.com>,
	Andreas Gruenbacher <agruen@...e.de>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	George Wilson <gcwilson@...ibm.com>
Subject: drop SECURITY_FILE_CAPABILITIES?

Hey,

Just a probe to see what people think.  I've seen two cases
in about the last month where software was confounded by
an assumption that prctl(PR_CAPBSET_DROP, CAP_SOMETHING)
would succeed if privileged, but not handling the fact
that SECURITY_FILE_CAPABILITIES=n means you can't do that.

Are we at the point yet where we feel we can get rid of
the SECURITY_FILE_CAPABILITIES=n case?

Note that there is a boot arg no_file_caps which prevents
file capabilities from being used if SECURITY_FILE_CAPABILITIES=y.
I think that's the case most users will care about, whereas the
remaining differences between CONFIG_SECURITY_FILE_CAPABILITIES=y
and =n are that with CONFIG_SECURITY_FILE_CAPABILITIES=y :

	(1) certain security hooks (task_setscheduler, task_setioprio, and
	task_setnice) do capability set comparisions,
	(2) it is possible to drop capabilities from the bounding set,
	(3) it is possible to set per-task securelevels,
	(4) and it is possible to add any capability to your inheritable
	set if you have CAP_SETPCAP.

Does anyone know of cases where CONFIG_SECURITY_FILE_CAPABILITIES=n
is still perceived as useful?

thanks,
-serge
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