On Mon, Jul 13, 2020 at 4:30 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: > On 2020-07-07 21:42, Paul Moore wrote: > > On Mon, Jul 6, 2020 at 10:50 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: > > > On 2020-07-05 11:09, Paul Moore wrote: > > > > On Sat, Jun 27, 2020 at 9:21 AM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: ... > > > > In the early days of this patchset we talked a lot about how to handle > > > > the task_struct and the changes that would be necessary, ultimately > > > > deciding that encapsulating all of the audit fields into an > > > > audit_task_info struct. However, what is puzzling me a bit at this > > > > moment is why we are only including audit_task_info in task_info by > > > > reference *and* making it a build time conditional (via CONFIG_AUDIT). > > > > > > > > If audit is enabled at build time it would seem that we are always > > > > going to allocate an audit_task_info struct, so I have to wonder why > > > > we don't simply embed it inside the task_info struct (similar to the > > > > seccomp struct in the snippet above? Of course the audit_context > > > > struct needs to remain as is, I'm talking only about the > > > > task_info/audit_task_info struct. > > > > > > I agree that including the audit_task_info struct in the struct > > > task_struct would have been preferred to simplify allocation and free, > > > but the reason it was included by reference instead was to make the > > > task_struct size independent of audit so that future changes would not > > > cause as many kABI challenges. This first change will cause kABI > > > challenges regardless, but it was future ones that we were trying to > > > ease. > > > > > > Does that match with your recollection? > > > > I guess, sure. I suppose what I was really asking was if we had a > > "good" reason for not embedding the audit_task_info struct. > > Regardless, thanks for the explanation, that was helpful. > > Making it dynamic was actually your idea back in the spring of 2018: > https://lkml.org/lkml/2018/4/18/759 If you read my comments from 2018 carefully, or even not so carefully I think, you'll notice that my primary motivation for using a pointer was to "hide" the audit_task_info struct contents so that they couldn't be abused by other kernel subsystems looking for a general container identifier inside the kernel. As we've discussed many times before, this patchset is not a general purpose container identifier, this is an ***audit*** container ID; limiting the scope and usage of this identifier is what has allowed us to gain the begrudging acceptance we've had thus far and I believe it is the key to success. For whatever it is worth, this patchset doesn't hide the audit_task_struct definition in a kernel/audit*.c file, it lives in a header file which is easily accessed by other subsystems. In my opinion we should pick one of two options: leave it as a pointer reference and "hide" the struct definition, or just embed the struct and simplify the code. I see little value in openly defining the audit_task_info struct and using a pointer reference; if you believe you have a valid argument for why this makes sense I'm open to hearing it, but your comments thus far have been unconvincing. > > > > Richard, I'm sure you can answer this off the top of your head, but > > > > I'd have to go digging through the archives to pull out the relevant > > > > discussions so I figured I would just ask you for a reminder ... ? I > > > > imagine it's also possible things have changed a bit since those early > > > > discussions and the solution we arrived at then no longer makes as > > > > much sense as it did before. > > > > > > Agreed, it doesn't make as much sense now as it did when proposed, but > > > will make more sense in the future depending on when this change gets > > > accepted upstream. This is why I wanted this patch to go through as > > > part of ghak81 at the time the rest of it did so that future kABI issues > > > would be easier to handle, but that ship has long sailed. > > > > To be clear, kABI issues with task_struct really aren't an issue with > > the upstream kernel. I know that you know all of this already > > Richard, I'm mostly talking to everyone else on the To/CC line in case > > they are casually watching this discussion. > > kABI issues may not as much of an upstream issue, but part of the goal > here was upstream kernel issues, isolating the kernel audit changes > to its own subsystem and affect struct task_struct as little as possible > in the future and to protect it from "abuse" (as you had expressed > serious concerns) from the rest of the kernel. include/linux/sched.h > will need to know more about struct audit_task_info if it is embedded, > making it more suceptible to abuse. I define "abuse" in this context as other kernel subsystems inspecting the contents of the audit_task_struct, most likely to try and approximate a general container identifier. Better separation between the audit subsystem and the task_struct, while conceptually nice, isn't critical and is easily changed upstream with each kernel release as it isn't part of the kernel/userspace API. Regardless, a basic conceptual separation is achieved by the audit_task_struct regardless of if it is embedded into the task_struct or included by a pointer reference. > > While I'm sympathetic to long-lifetime enterprise distros such as > > RHEL, my responsibility is to ensure the upstream kernel is as good as > > we can make it, and in this case I believe that means embedding > > audit_task_info into the task_struct. > > Keeping audit_task_info dynamic will also make embedding struct > audit_context as a zero-length array at the end of it possible in the > future as an internal audit subsystem optimization whereas largely > preclude that if it were embedded. Predicting the future is hard, but I would be comfortable giving up on a variable length audit_task_info struct. Besides, if we *really* had to do that in the future we could, it's not part of the kernel/userspace API. > This method has been well exercised over the last two years of > development, testing and rebases, so I'm not particularly concerned > about its dynamic nature any more. It works well. At this point this > change seems to be more gratuitously disruptive than helpful. It may not seem like it, but at this point in this patchset's life I do try to limit my comments to only those things which I feel are substantive. In the cases where I think something is borderline I'll mention that in my comments. The trivial cases I'll generally call out as "nitpicks". I assure you my comments are not gratuitous. I look forward to reviewing another round of this patchset about as much as I expect you look forward to writing, testing, and submitting it. > > > > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c > > > > > index 468a23390457..f00c1da587ea 100644 > > > > > --- a/kernel/auditsc.c > > > > > +++ b/kernel/auditsc.c > > > > > @@ -1612,7 +1615,6 @@ void __audit_free(struct task_struct *tsk) > > > > > if (context->current_state == AUDIT_RECORD_CONTEXT) > > > > > audit_log_exit(); > > > > > } > > > > > - > > > > > audit_set_context(tsk, NULL); > > > > > audit_free_context(context); > > > > > } > > > > > > > > This nitpick is barely worth the time it is taking me to write this, > > > > but the whitespace change above isn't strictly necessary. > > > > > > Sure, it is a harmless but noisy cleanup when the function was being > > > cleaned up and renamed. It wasn't an accident, but a style preference. > > > Do you prefer a vertical space before cleanup actions at the end of > > > functions and more versus less vertical whitespace in general? > > > > As I mentioned above, this really was barely worth mentioning, but I > > made the comment simply because I feel this patchset is going to draw > > a lot of attention once it is merged and I feel keeping the patchset > > as small, and as focused, as possible is a good thing. > > Is this concern also affecting the perspective on the change from > pointer to embedded above? Keeping this particular patchset small and focused has always been a goal; I know we talked about this at least once, likely more than that, while I was still at RH and we were talking offline. If something is going to be contentious, it is better to be small and focused on the contention. -- paul moore www.paul-moore.com
