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Re: [libvirt] [PATCH v5 3/3] security_dac: Favour ACLs over chown()



On Thu, Mar 28, 2013 at 11:38:04AM +0100, Michal Privoznik wrote:
> On 28.03.2013 10:46, Daniel P. Berrange wrote:
> > On Thu, Mar 21, 2013 at 05:50:49PM +0100, Michal Privoznik wrote:
> >>  #define VIR_FROM_THIS VIR_FROM_SECURITY
> >>  #define SECURITY_DAC_NAME "dac"
> >> +#define SECURITY_DAC_XATTR_OLD_ACL "trusted.libvirt.dac.oldACL"
> >> +#define SECURITY_DAC_XATTR_OLD_OWNER "trusted.libvirt.dac.oldOwner"
> >> +#define SECURITY_DAC_XATTR_REFCOUNT "trusted.libvirt.dac.refCount"
> > 
> > IMHO we don't need the 'trusted.' prefix on these.
> > 
> > Daniel
> > 
> 
> An XATTR has to have a prefix. We can choose from several prefixes.
> attr(5) says:
> 
>   Currently the security, system, trusted, and user extended attribute
>   classes are defined as described below. Additional classes may be
>   added in the future.
> 
> security - should be used by kernel security modules, such as Security
> Enhanced Linux. As long as libvirt doesn't provide kernel module, we
> should not be polluting this prefix.
> 
> system - used by the kernel to store system objects such as Access
> Control Lists and Capabilities. Again, we are not kernel.
> 
> trusted - visible and accessible only to processes that have the
> CAP_SYS_ADMIN capability (the super user usually has this capability).
> Attributes  in  this  class are used to implement mechanisms in user
> space (i.e., outside the kernel) which keep information in extended
> attributes to which ordinary processes should not have access.
> 
> Note, that the three above can be touched only by root (or
> CAP_SYS_ADMIN'ed process).
> 
> user -  may be assigned to files and directories for storing arbitrary
> additional information such as the mime type, character set or encoding
> of a file.
> 
> The user. can be manipulated by ordinary user.
> 
> My rationale for not allowing ordinary user to play with our XATTRs is
> to prevent them chowning to arbitrary user.

Ok, that makes more sense now. I wonder how portable this list of
prefixes is though - does anyone know if *BSD use the same conventions ?


Daniel
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