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Re: Announcement: Solaris loadable kernel module backdoor
From: weinmann () RBG INFORMATIK TU-DARMSTADT DE (Ralf-Philipp Weinmann)
Date: Sun, 26 Dec 1999 18:01:33 +0100


Keith Owens <kaos () OCS COM AU> writes:

On Tue, 21 Dec 1999 14:33:50 -0800,
pedward () WEBCOM COM wrote:
At boot, compile the list of modules that are 'known good' (for the sake
of argument, it's the /lib/modules/x.y.z), then write the list, with
MD5 checksums, to a write once /proc interface to kmod.

kmod would check the MD5 sum before loading the requested module, if it didn't
match the in-kernel list, don't allow it.

kmod does not load modules.  It starts a kernel thread and invokes
modprobe.  modprobe runs /etc/modules.conf and the the dependency chain
then loads anywhere between zero and n modules.  All of this work is in
user space and it is all outside kernel control.

However I'd like to point out that you could add call a routine to
compute the MD5 or SHA-1 hash of the data copied with copy_from_user()
in sys_init_module() and reject it if it doesn't match a precomputed
value (which has to be securely stored somewhere in kernel space for
each and every module that the is allowed to be loaded).
A scheme I'd prefer would be to have a trusted signing key in the kernel
and allow the user to write a signed list of modules and their
respective hash values to say /proc/securemodules. This allows for
utmost flexibility and security IMHO.

-rpw

--
Ralf-P. Weinmann (weinmann () rbg informatik tu-darmstadt de)
PGP key len/id/fingerprint: 2048/09AAEEAA1/46C772078ACB58DEF6EBF8030CBF1724
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