Re: [PATCH ghak90 V9 01/13] audit: collect audit task parameters

On Mon, Jul 6, 2020 at 10:50 PM Richard Guy Briggs <rgb(a)redhat.com&gt; wrote: > On 2020-07-05 11:09, Paul Moore wrote: > > On Sat, Jun 27, 2020 at 9:21 AM Richard Guy Briggs <rgb(a)redhat.com&gt; wrote: > > > > > > The audit-related parameters in struct task_struct should ideally be > > > collected together and accessed through a standard audit API. > > > > > > Collect the existing loginuid, sessionid and audit_context together in a > > > new struct audit_task_info called "audit" in struct task_struct. > > > > > > Use kmem_cache to manage this pool of memory. > > > Un-inline audit_free() to be able to always recover that memory. > > > > > > Please see the upstream github issue > > > https://github.com/linux-audit/audit-kernel/issues/81 > > > > > > Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com&gt; > > > Acked-by: Neil Horman <nhorman(a)tuxdriver.com&gt; > > > Reviewed-by: Ondrej Mosnacek <omosnace(a)redhat.com&gt; > > > --- > > > include/linux/audit.h | 49 +++++++++++++++++++++++------------ > > > include/linux/sched.h | 7 +---- > > > init/init_task.c | 3 +-- > > > init/main.c | 2 ++ > > > kernel/audit.c | 71 +++++++++++++++++++++++++++++++++++++++++++++++++-- > > > kernel/audit.h | 5 ++++ > > > kernel/auditsc.c | 26 ++++++++++--------- > > > kernel/fork.c | 1 - > > > 8 files changed, 124 insertions(+), 40 deletions(-) > > > > > > diff --git a/include/linux/audit.h b/include/linux/audit.h > > > index 3fcd9ee49734..c2150415f9df 100644 > > > --- a/include/linux/audit.h > > > +++ b/include/linux/audit.h > > > @@ -100,6 +100,16 @@ enum audit_nfcfgop { > > > AUDIT_XT_OP_UNREGISTER, > > > }; > > > > > > +struct audit_task_info { > > > + kuid_t loginuid; > > > + unsigned int sessionid; > > > +#ifdef CONFIG_AUDITSYSCALL > > > + struct audit_context *ctx; > > > +#endif > > > +}; > > > + > > > +extern struct audit_task_info init_struct_audit; > > > + > > > extern int is_audit_feature_set(int which); > > > > > > extern int __init audit_register_class(int class, unsigned *list); > > > > ... > > > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > > index b62e6aaf28f0..2213ac670386 100644 > > > --- a/include/linux/sched.h > > > +++ b/include/linux/sched.h > > > @@ -34,7 +34,6 @@ > > > #include <linux/kcsan.h> > > > > > > /* task_struct member predeclarations (sorted alphabetically): */ > > > -struct audit_context; > > > struct backing_dev_info; > > > struct bio_list; > > > struct blk_plug; > > > @@ -946,11 +945,7 @@ struct task_struct { > > > struct callback_head *task_works; > > > > > > #ifdef CONFIG_AUDIT > > > -#ifdef CONFIG_AUDITSYSCALL > > > - struct audit_context *audit_context; > > > -#endif > > > - kuid_t loginuid; > > > - unsigned int sessionid; > > > + struct audit_task_info *audit; > > > #endif > > > struct seccomp seccomp; > > > > 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.

From an upstream perspective, I think embedding the audit_task_info struct is the Right Thing To Do. The code is cleaner and more robust if we embed the struct.

> > 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.

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.

> I didn't make > that argument then and I regret it now that I realize and recall some of > the thinking behind the change. Your reasons at the time were that > contid was the only user of that change but there have been some > CONFIG_AUDIT and CONFIG_AUDITSYSCALL changes since that were related. Agreed that there are probably some common goals and benefits with those changes and the audit container ID work, however, I believe that discussion quickly goes back to upstream vs RHEL.

> > > 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.

However, I'm not going to lose even a second of sleep over a single blank line gone missing ;) paul moore