On Sun, Nov 28, 2021 at 01:00:28PM -0500, James Bottomley wrote: > On Sun, 2021-11-28 at 09:18 -0600, Serge E. Hallyn wrote: > > On Sun, Nov 28, 2021 at 08:29:21AM -0500, James Bottomley wrote: > > > On Sat, 2021-11-27 at 22:45 -0600, Serge E. Hallyn wrote: > > > > On Sat, Nov 27, 2021 at 04:45:47PM +0000, James Bottomley wrote: > > > > > As a precursor to namespacing IMA a way of uniquely identifying > > > > > the namespace to appear in the IMA log is needed. This log may > > > > > be transported away from the running system and may be analyzed > > > > > even after the system has been rebooted. Thus we need a way of > > > > > identifying namespaces in the log which is unique. UUID, being > > > > > designed probabilistically never to repeat, fits this bill so > > > > > add it to the user_namespace which we'll also use for > > > > > namespacing IMA. > > > > > > > > If the logs run across 5 boots, is it important to you that the > > > > uuid be unique across all 5 boots? Would it suffice to have a > > > > per-boot unique count and report that plus some indicator of the > > > > current boot (like boot time in jiffies)? > > > > > > For the purposes of IMA it's only really important to have the uuid > > > be unique within the particular log ... i.e. unique per > > > boot. However, given the prevalence of uuids elsewhere and the > > > fact we have no current per-boot unique label for the namespace > > > (the inode number could repeat), it seemed reasonable to employ > > > uuids for this rather than invent a different identifier. Plus IMA > > > isn't going to complain if we have a globally unique identifier ... > > > > Ok - Note I'm not saying I heavily object, but I'm mildly concerned > > about users who happen to spin off a lot of user namespaces for > > quick jobs being penalized. > > Well, that's why I use the uuid_gen coupled to prandom ... there > shouldn't be a measurable overhead generating it. Does prandom have *no*, or just little effect on the entopy pool? Tried briefly looking at prandom_u32, not quite getting how it's using net_rand_state - it reads it and uses it but doesn't make any changes to it? > > I suspect Eric will also worry about the namespacing implications - > > i.e. people *will* want to start restoring user namespaces with a > > previously used uuid. > > So this is a problem I tried to address in the last paragraph. If I > put any marker on a namespace, people are potentially going to want to > save and restore it. The bottom line is that ima logs are add only. > You can't save and restore them so we're already dealing with something > that can't be CRIU transported. I had hoped that it would be obvious > that a randomly generated uuid, whose uniqueness depends on random > generation likewise can't be saved and restored because we'd have no > way to prevent a clash. Yes but you're making this a general user_namespace struct member. So once that's there people will want to export it, use it for things other than ima. > > So given that 'unique per boot' is sufficient, what would be the > > problem with simply adding a simple ever-increasing unique atomix > > count to the struct user_namespace? > > I don't think there is any ... but I equally don't see why people would > want to save and restore the uuid but not the new monotonic identifier > ... because it's still just a marker on a namespace. But you've called it "the namespace uuid". I'm not even really thinking of checkpoint/restart, just stopping and restarting a container. I'm convinced people will want to start using it because, well, it is a nice feature. -serge
