Re: another kconfig target for building monolithic kernel (for security) ?

[devzero@web.de]

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 <nix@esperi.org.uk>
> Gesendet: 30.04.06 12:57:49
> An: Arjan van de Ven <arjan@infradead.org>
> CC: davej@redhat.com, linux-kernel@vger.kernel.org
> 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, devzero@web.de 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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