hello !
thanks for help - i found that there seems another way for securing /dev/{k}mem (at least in recent kernels) - the docomentation for the "BSD Secure Levels Linux Security Module" (at Documentation/seclvl.txt) tells:
Level 1 (Default):
- /dev/mem and /dev/kmem are read-only
- IMMUTABLE and APPEND extended attributes, if set, may not be unset
- Cannot load or unload kernel modules
- Cannot write directly to a mounted block device
- Cannot perform raw I/O operations
- Cannot perform network administrative tasks
- Cannot setuid any file
so - no need for compiling a static/monolithic kernel anymore !?
regards
roland
> -----Ursprüngliche Nachricht-----
> Von: Nix <[email protected]>
> Gesendet: 30.04.06 12:57:49
> An: Arjan van de Ven <[email protected]>
> CC: [email protected], [email protected]
> Betreff: Re: another kconfig target for building monolithic kernel (for security) ?
> On 29 Apr 2006, Arjan van de Ven prattled cheerily:
> > On Sat, 2006-04-29 at 12:43 -0400, Dave Jones wrote:
> >> On Sat, Apr 29, 2006 at 03:03:55PM +0200, [email protected] wrote:
> >>
> >> > i want to harden a linux system (dedicated root server on the internet) by recompiling the kernel without support for lkm (to prevent installation of lkm based rootkits etc)
> >>
> >> Loading modules via /dev/kmem is trivial thanks to a bunch of tutorials and
> >> examples on the web, so this alone doesn't make life that much more difficult for attackers.
> >
> > /dev/kmem should be a config option too though
>
> Yeah, but in practice this should work (somewhat old patch, should still
> apply):
>
> diff -durN 2.6.14-seal-orig/include/linux/capability.h 2.6.14-seal/include/linux/capability.h
> --- 2.6.14-seal-orig/include/linux/capability.h 2005-10-29 15:15:00.000000000 +0100
> +++ 2.6.14-seal/include/linux/capability.h 2005-10-29 15:25:48.000000000 +0100
> @@ -311,7 +311,7 @@
>
> #define CAP_EMPTY_SET to_cap_t(0)
> #define CAP_FULL_SET to_cap_t(~0)
> -#define CAP_INIT_EFF_SET to_cap_t(~0 & ~CAP_TO_MASK(CAP_SETPCAP))
> +#define CAP_INIT_EFF_SET to_cap_t(~0 & ~CAP_TO_MASK(CAP_SETPCAP) & ~CAP_TO_MASK(CAP_SYS_RAWIO))
> #define CAP_INIT_INH_SET to_cap_t(0)
>
> #define CAP_TO_MASK(x) (1 << (x))
>
> > (and /dev/mem should get the filter patch that fedora has ;-)
>
> Agreed.
>
> --
> `On a scale of 1-10, X's "brokenness rating" is 1.1, but that's only
> because bringing Windows into the picture rescaled "brokenness" by
> a factor of 10.' --- Peter da Silva
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