[linux-audio-dev] LSM: Linux 2.6 Kernel Capability LSM Module Local Privilege Elevation

[Jack O'Quin]

Hans Fugal <hans at fugal.net> writes:

> On Wed, 29 Dec 2004 at 11:07 +0100, Frank Barknecht wrote:
>> Hallo,
>> Fernando Lopez-Lezcano hat gesagt: // Fernando Lopez-Lezcano wrote:
>> 
>> > Why I think this is a yes. Any kernel that wants to use the realtime-lsm
>> > will have to either not build the POSIX capabilities lsm, or build it as
>> > a module. In the later case the system will be vulnerable. The
>> > realtime-lsm does not depend on the POSIX capabilities lsm but it forces
>> > you to build it as a module, 
>> 
>> I don't understand: Why does it do so? Shouldn't this be "fixed" in
>> the realtime-lsm then?

Actually, the bug is not in either.  The "fix" is in security/dummy.c.

> Someone please correct me if I'm wrong, but it just looks like a case of a
> simplistic check. It doesn't look like realtime-lsm really depends on
> posix capabilities being compiled as a module, but on posix capabilities
> not being compiled in. So I'm going to try this patch (it builds, we'll
> see if it works fine, but I suspect it will):

The actual source code is in security/Kconfig...

config SECURITY_REALTIME
	tristate "Realtime Capabilities"
	depends on SECURITY && SECURITY_CAPABILITIES!=y
	default n
	help
	  This module selectively grants realtime privileges
	  controlled by parameters set at load time or via files in
	  /sys/module/realtime/parameters.

	  If you are unsure how to answer this question, answer N.

The reason for this check is that realtime-lsm does not work when the
capability LSM is installed built-in (i.e. not as a module).  I am not
a wizard at Kconfig.  Perhaps someone more skilled in this area can
explain what to do.  Note that capability is not needed when realtime
is installed.
-- 
  joq