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

On Thu, Mar 28, 2013 at 12:47:25PM +0100, Michal Privoznik wrote: > On 28.03.2013 12:12, Daniel P. Berrange wrote: >> 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 >> > > Aah. On BSD they support just 'system' and 'user': > > http://svnweb.freebsd.org/base/head/sys/sys/extattr.h?revision=184413&... > > Does it mean we should move from 'trusted' to 'system'? Or is > conditional prefix ('trusted' on linux, 'system' on BSD) sufficient? You're not able to use 'system.' from userspace. # setfattr -n user.eek -v bar foo # setfattr -n system.eek -v bar foo setfattr: foo: Operation not supported So 'user.' is the only option here for BSD. If we consider the (admittedly unlikely) possibility of an NFS server access by 2 libvirt clients one running Linux and one running BSD, we want compatibility. So this says to me that we should use 'user.' as the prefer everywhere.

Regards, Daniel